2013 Astronomical Calendar Preview by UniversalWorkshop.com

Cover picture “The Moon is a mystery”: this was the answer given to me by the president of the International Flat Earth Society during our radio debate (www.universalworkshop.com/Litfoam/FlatEarth.htm). I had no real hope that he would listen to, let alone be persuaded by, the other arguments I had prepared, but the Full Moon is surely a simple clincher. We see its circular face staring down at us; if the bright part of it is the half on which the Sun is shining—and by watching it through the other phases we are compelled to see that it is—then this must mean that the Sun is down in the opposite direction, under the ground-level we stand on. —No good: “The Moon is a mystery.” Indeed it is; it has been taken for a f lying saucer, shot at with rif les. I remember a long ride on the back of a pickup truck through a desert before dawn and the driver stopping and asking: “What’s that over there?” He thought it was the lighted porch of a lonely trading post where we might get something to eat; it was the horns of the Moon rising through bars of cloud. You could say there is a paradox for each phase of the Moon. The famous one is the Moon Illusion: when the Moon is down low to the horizon it seems strikingly larger in our eyes (though it actually subtends a smaller angle, because of refraction and because more distant than when it is in the middle of the sky). And this, which has had books written about it and has scarcely been explained, is best seen when the Moon is Full. The New Moon is a mystery in a different way: we infer it happens but can never see it—except at a solar eclipse, when the Moon suddenly manifests itself out of empty sky, and only as a silhouette. The paradox I associate with the Last Quarter Moon (though it applies better to any Moon that is clearly just past Full) isn’t really paradoxical and yet it carries a frisson of surprise; it is one of those observations that make astronomical space jump into three dimensions. You see the Sun go down over to your right in the west, and some time later you notice the Moon above the horizon to your left. And its bright face. pointing slantingly downward, is evidently receiving a stream of sunlight that is coming up on the other side of Earth from that on which the Sun went down. The Sun has slid around in some vast cavity behind you, and at this moment you feel the free-f loatingness of the world you stand on. It is rather as if you thought you were in a house; then through a window notice water f lowing toward you, and through an opposite window notice water f lowing away, and realize you are on a ship. From a small town called Vernazza we watched the Sun go down—it became a point exactly in that notch between sections of the mountain line farther west along the Ligurian coast of Italy. An hour or so later, long enough for the sky to go black, we noticed the brilliant Moon above the dark rooftops. It lay in a wash of its own dazzle, but within this it was a solid white D, because this was the moment of First Quarter, on the evening of May 28 last year. Why does its D-shaped face gaze in a direction almost parallel to the horizon, instead of downward toward the Sun from which it is receiving its light? You could call this the First-Quarter Moon paradox, since this is when it is most plainly displayed. The illuminated face does point straight toward the Sun, but what is “straight”? We are accustomed to thinking of the horizon as the straight line. Both the horizon and the ecliptic (the line along which the Sun travels and the Moon approximately travels) are straight in the sense that they are “great circles” around the sky. If we painted this picture on the inside of a coconut shell, the horizon would be a f lat line encircling the shell, and the ecliptic would be another such f lat line, along which the Moon would face straight toward the Sun. But when we draw on f lat canvas, we have to choose only one great circle to be f lat. Or: e

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The Moon was in Leo (actually it was under his feet, dipping through the little constellation Sextans). Just up-right from the Moon was Regulus and just upleft from it Mars—it had passed Regulus during the day and would pass Mars during the night. And that bright dot in the notch where the Sun set, like a memory of the Sun’s last glint, is Venus, though it couldn’t really be seen. It was following the Sun down by about an hour (to venture accurately in front of it, just four days later, at that rare event called a transit). At this First Quarter moment it’s ninety degrees, a quarter of the circle, from Moon to Sun. I thought that in the picture I had got this distance compressed, or the Moon’s height exaggerated—it’s a habit of our perception to exaggerate the vertical at the expense of the horizontal—but it turns out to be about right. There may be some time-compression between twilight and black night sky. In Italy I found myself making Italy-shaped pictures, slanting from upper left to lower right, so as to get things in that were far apart. As it happens (because the latitude of the place is near 45° and so is the slant of the ground as I’ve drawn it, if you hold the picture in “landscape mode,” the long edge is parallel to a third great circle: the equator. So the North Pole Star is straight upward, and the scene is a magnified view of the edge of an Earth globe that you are holding upright in your hands. Tilted views like this, as if from off the planet in space, can make us feel that it really is a f loating globe, on which we cling like dust. The town, like many on Italy’s steep coasts, consists of streetless piles of houses on either side of a former stream, now the only street, descending to the piaz-

za and the harbor. Our room (the lighted window) was approached not up stairs but up paths climbing inside the mass. The right-hand mass ends in the church, dedicated to Santa Margherita of Antioch and standing on a terrace with under it what looks like a walled-up cave. In a small street near the middle of Florence there is another church of Santa Margherita, where Dante is said to have seen Beatrice for the first time (she was eight and he nine) and where Beatrice is buried. He saw her only once more, nine years later. He married another (Gemma Donati, in 1285) and so did she (Simone de’ Bardi, in 1287), and she died in 1290 at age 24. The great poem which Dante called just Comedy (because it ends—to say the least—happily and because comedy did not have its modern meaning of “farce) starts with him Nel mezzo del cammin’ di nostra vita, “At the midpoint of the highway of our life,” that is, at the age of 35, on the day before Good Friday (March 24, I think) in the year 1300, lost in a dark forest and confronted by terrible beasts. From heaven Beatrice (whose “eyes outshone the light of any star”) sees him and sends to rescue him the poet Virgil, his predecessor (by thirteen centuries) as composer of an Italian epic. Virgil first guides Dante down into hell, the Inferno, whose description constitutes the first of the three books of the Divine Comedy (as it later became called). We don’t know where the dark forest of Dante’s despair was, in which he and his guide found an arched entrance into the Inferno. They descended through its nine circles, meeting and conversing with examples of every kind of sinner, and at the bottom the very worst, the traitors to their lords and benefactors: Judas Iscariot who took a bribe, Brutus and Cassius who stabbed the dictator Julius Caesar, and Lucifer who rebelled against God. I would put quite others at the bottom of my Inferno. Lucifer, “bearer of light,” was a title for the morning star, Venus, but strangely became applied to the fallen angel Satan. Virgil and Dante pass “the point to which all weight on every side pulls down” (the center of the Earth) and then by using the gigantic shaggy body of Lucifer as a ladder they climb out; salimmo sù, el primo e io secondo, tanto ch’i’ vidi de le cose belle che porta ’l ciel, per un pertugio tondo. E quindi uscimmo a riveder le stelle. We struggled up, first he and second I, Till I could see, as if through prison bars, Some of the lovely things that grace the sky. Thence came we out, to rebehold the stars. (A mischievous translation, I’m afraid. Dante says “through a round aperture,” not “through prison bars.” I’m thinking not only of the rhyme but of prisoners I’ve known of, who longed to see the stars, or drew comfort from or were absolved by glimpsing them or learning about them, or were overjoyed to see them on coming out.) That’s how the Inferno ends. The second book, the Purgatorio, begins with what Dante immediately sees: Lo bel pianeto che d’amar conforta, “the fair planet that empowers love”—Venus. So I imagine his point of emergence from the underworld to be the cave under this other church of Santa Margherita, with Venus on the skyline. Unfortunately that can’t be, because he says that the planet was “making the whole east smile” and was in Pisces, “veiling the Fishes that were in her train.” And, turning to the right, he looked “to the other pole, and saw four stars, never before seen except by the primeval people,” non viste mai fuor che alla prima gente—the Southern Cross. “The sky seemed to rejoice in their sparkling; oh widowed region of the north, denied that sight!” Dante has penetrated through the Earth and emerged on the other side. The Inferno (a pit made by the fall of Lucifer) is under Jerusalem; at its antipodes, in an ocean that fills the southern hemisphere, is an island on which rises the Mount of Purgatory. In 1300 few if any Europeans had explored south of the equator and thus seen the other celestial pole, though plenty had been as far as Egypt and seen the Southern Cross. And Dante, without having been able to see those lands and constellations that the Earth hides, understood that it is a globe and that the Sun and stars roll around it; the time, he says, was sunset at Jerusalem and sunrise at Mount Purgatory. Virgil guides him up its seven levels, on which the redeemable sinners undergo their purification; on the highest terrace are those whose sins were caused by too much love. Toward the summit Virgil, being a pagan who can go no further, is replaced as guide by Beatrice, and she leads Dante through the Earthly Paradise, a Garden of Eden for those who have become innocent enough to qualify for Paradise itself. He drinks from the river and, like a tree with its spring foliage, has become “pure and made fit to shoot up to the stars”— puro e disposto a salire alle stelle. Thus with that same lilting word closes the epic’s second book, finished perhaps four or five years after the first. The third book, Paradiso, is the journey into heaven, through the concentric spheres that (in the cosmic picture accepted from ancient times until three centuries after Dante) revolve around stolid Earth: first that of the Moon, where live the souls whose virtue waxes and wanes; on up to the other symbolic planets including (between Venus and Mars) the Sun, to the eighth sphere, of the stars and saints, and the ninth, of the angels— this sphere is the Primum Mobile, which is turned by God and causes the lower spheres to turn like cogs. And finally beyond physical space to the Empyrean, a realm of light which makes Beatrice more beautiful than ever and which reveals to him the mystery of the Trinity; he feels himself turned like a smooth wheel, along with the cosmos, by “the love that moves the Sun and the other stars”— l’amor che muove il sole e l’altre stelle. Thus ends the Paradiso, from whose beatific vision Dante returned to the petty world of Italian politics where he was usually on the losing side and always without Beatrice.

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VIEWS TOWARD THE MOON at successive stages of its encounter with the Earth’s shadow. This is what can be seen from almost everywhere on the night side of the Earth. The umbra and penumbra are represented by cross-sections through them at the distance where the Moon is. They are visible only where they fall on the Moon. The umbra has a fairly abrupt edge; its darkness and color vary with atmospheric conditions ο Sco around the Earth. The penumbra is imperceptible except in its inner part. The umbra gets narrower as it goes farther away; the penumbra, wider. A circle between them represents the size of the body casting the shadows: the Earth we are standing on. Arrows show the motion of the shadow and the Moon over a span of 8 hours. The Moon moves faster because it takes only a month to go around the sky, while the shadow (like the Sun opposite to it) takes a year. However, since the shadow does move along somewhat during the eclipse, the diagram, representing the relation of the Moon to the circular umbra and penumbra, cannot be exactly true in all respects: the Moons ought to be slightly wider apart. Any star shown in the field is plotted in relation to the Moon and shadow at the middle moment of the eclipse—and as seen from the center of the Earth.

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Penumbral Lunar Eclipse, October 18-19 Oct. 18, 21:50—Penumbral eclipse begins; first contact of Moon with Earth’s shadow. 23:37—Full Moon (Moon at opposition to the Sun in ecliptic longitude). Moon’s center is exactly north of center of Earth’s shadow, as measured perpendicularly to ecliptic. 23:38—Moon at opposition to Sun in right ascension; its center is exactly north of center of Earth’s shadow, as measured perpendicularly to ecliptic. 23:51—Middle of eclipse: Moon nearest to center of Earth’s shadow. The penumbral magnitude of the eclipse is 0.7649; that is, the penumbra reaches across that fraction of the Moon’s diameter. Oct. 19, 01:49—Penumbral eclipse ends: last contact of Moon with Earth’s shadow. ARIES 21:48—Moon’s center reaches descending node through ecliptic. Oct. 25, 14:04 —Moon at apogee. 251,380 mi (404,557 km). Oct. 30, 19:46:43—Middle of eclipse season: Sun at same longitude as ascending node. This is eclipse number 52 of the 72 in lunar saros series 117 (1094 Apr. 3 to 2356 May 15).

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Penumbral Lunar Eclipse, May 25 May 7, 07:13:10—Middle of eclipse season: Sun at same longitude as ascending node. May 24, 00:35—Moon’s center reaches ascending node through ecliptic. May 25, 03:53—Penumbral eclipse begins; first contact of Moon with Earth’s shadow. 04:11—Middle of eclipse: Moon nearest to center of Earth’s shadow. The penumbral magnitude of the eclipse is 0.0157; that is, the penumbra reaches across that fraction of the Moon’s diameter. 04:24—Moon at opposition to Sun in right ascension; its center is exactly north of center of Earth’s shadow, as measured perpendicularly to ecliptic. 04:25—Full Moon (Moon at opposition to the Sun in ecliptic longitude). Moon’s center is exactly north of center of Earth’s shadow, as measured perpendicularly to ecliptic. Oph 04:26—Penumbral ψeclipse ends: last contact of Moon with Earth’s shadow. May 26, 01:57—Moon at perigee. 222,685 mi (358,377 km). This is eclipse number 1 of the 71 in lunar saros series 150 (2013 May 25 to 3275 June 30).

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Partial lunar eclipse, April 25 April 25, 18:03—penumbral eclipse begins; first contact of Moon with Earth’s shadow. 19:54—partial eclipse begins; first contact of Moon with Earth’s umbra. 19:57—Full Moon (Moon at opposition to the Sun in ecliptic longitude). Moon’s center is exactly south of the center of the Earth’s shadow as measured perpendicularly to the ecliptic. 19:58—Moon at opposition to the Sun in right ascension; its center is exactly south of center of Earth’s shadow as measured perpendicularly to the equator. 20:07—middle of eclipse: Moon is nearest to center of Earth’s shadow. The umbral magnitude of the eclipse is 0.0148; that is, the umbra reaches across that fraction of the Moon’s diameter. 20:21—partial eclipse ends; last contact of Moon with Earth’s umbra. 22:11—penumbral eclipse ends; last contact of Moon with Earth’s shadow. April 26, 14:07—Moon’s center reaches acending node through ecliptic. May 7, 07:13:10—Middle of eclipse season: Sun at same longitude as ascending node. This is eclipse number 65 of the 72 in lunar saros series 112 (859 May 20 to 2139 July 12).

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In the timetables, all times are given in Universal Time (UT).

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A five-eclipse year, two of the Sun and three of the Moon. A total eclipse of the Sun—dramatic though not very long—cuts across central Africa in early November. Few will travel to Australasia for the ring eclipse in May. The three lunar eclipses are all slight; the one occurring in October is available only to those living in eastern North America. Eclipses arrange themselves in “eclipse seasons,” typically two per year, each with an eclipse of either kind (lunar and solar). This year we will have three lunar and two solar eclipses. The seasons are centered around the times when the lines of the nodes of the Moon’s orbit point through the Sun, allowing eclipses to happen. These seasons, being slightly less than six months apart, fall about 18 days earlier each year; last year one season encompassed the last part of May into early June and the other was in November. This year one eclipse season spans late April into early May, while the other lasts from late October into early November. My usual thanks are in order to Mr. Raymond Brooks of Star Engineering in Arizona, for providing the precise times for the midpoints of the eclipse seasons, as well as reviewing my original manuscript and making helpful suggestions. In addition, my thanks to meteorologist Jay Anderson for all the raw climatological data and narrative summaries which are available online at eclipser.ca, a web page devoted to eclipses, transits, occultations and other astronomical events in which weather conditions play an important role. Go to: http://home.cc.umanitoba.ca/~jander/

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SCHEMATIC VIEW summarizing the year’s eclipses. At each date of new or full Moon, the Earth is shown with the Moon inward of it at new Moon, outward at full Moon. The plane of the Moon’s orbit at the time is shown in blue, paler for the half lying south of the ecliptic. This plane gradually rotates backward. There is an eclipse if the Moon is full or new when it is in the ecliptic plane, that is, close to the time it crosses the ascending node of its orbit or the opposite descending node. The black arrow is the moon’s course over 7 days. The view is from ecliptic longitude 270°, latitude 30°. Relative to the Earth’s orbit, the Sun’s size is exaggerated by 15, Earth and Moon by 600, and the Earth-Moon distance by 40; the inclination of the Moon’s orbit is exaggerated from 5° to 10°.

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Astronomical Calendar 2013

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Astronomical Calendar 2013

The three lunar eclipses I. April 25—Partial Eclipse of the Moon On this night of the full Moon, if you’re watching from the Eastern Hemisphere, you will see the planet Saturn, shining sedately with a yellow-white glow, about 5° above and to the left of the Moon. Below and to the right of Saturn, along with the Moon, but unseen in the blackness of space, is the shadow of our Earth, pointing away from the Sun (which from this vantage point lies somewhere below our feet). For North America, none of this eclipse will be visible since the actual instant of full Moon comes during the afternoon hours of April 25 with the Moon below the horizon. At 18:04 UT, the Moon begins to meet the Earth’s shadow; a little over two hours later it arrives under the middle of that shadow. By then the Moon will have just risen and will be visible low to the east-southeast horizon as seen from Ireland, or will be setting over south-central Japan in the morning hours of April 26. The Moon is sloping north in its orbit and, just a bit over 18 hours after reaching its full phase, it will reach its ascending node through the ecliptic plane. Thus it misses the center of the Earth’s shadow by 1.012 of an Earth radius (this is the quantity called gamma that expresses how central an eclipse is; in this particular case not very central). During the first 110 minutes the Moon’s northern hemisphere pushes ever-so-gradually into the partial shadow, called the penumbra. The outer two-thirds of this are too subtle to detect; but perhaps by 19:20 UT you may realize you are beginning to detect the gradient of soft grey darkening. At 19:54 UT, the Moon’s northern limb finally makes contact with a much more abrupt shadow, the blackish-brown umbra. This chord of shadow on the Moon grows and retreats over a span of

less than half an hour; at its deepest the umbra magnitude peaks at a puny 0.0148 as the Moon’s northern limb dips less than half an arc minute into the umbral shadow. This dark shadow’s coverage can be described as feeble at best; to the unaided eye even for those with acute visual skills it will hardly cause a perceptible dent of darkness on the lunar disk. The middle of the eclipse, at 20:07 UT, is in the midst of the midnight sky with the Moon directly overhead as seen from the western Indian Ocean and several hundred kilometers to the east of the island nation of Madagascar.

III. May 25—Penumbral Eclipse of the Moon One month after the Earth’s shadow passed over the Moon’s northern hemisphere, and just over two weeks after an annular solar eclipse, the penumbra once again makes contact (barely) with the Moon. Being in the same eclipse season, the two lunar eclipses occur at the same node (the descending one) of the Moon’s orbit. But whereas last month’s lunar eclipse belonged to an old saros cycle, this month’s is the very first of a brand new series—number 150. Hence the passage of the Moon’s disk into the Earth’s shadow will result in one of the slightest eclipses of all, administering a mere touch of penumbral shadow at the northernmost part of the lunar limb. This is the point of greatest eclipse, where the penumbral magnitude will only reach 0.0157; the penumbral shadow will be in contact with the Moon for little more than 33 minutes. It will thus be impossible to notice anything out of the ordinary concerning the Moon’s overall appearance. But to quote the well-known Belgian eclipse calculator Jean Meeus, the mention of such a slight and undistinguishable event is done “only for reason of completeness; the statistics of

VIEWS FROM THE MOON toward Earth and Sun. The viewpoint is for an observer lying on his back on the midpoint of the Moon, with the Earth at the zenith. The event, which is for us an eclipse of the Moon, is for this man-on-the-Moon an eclipse of the Sun. If he were to move farther north, the Earth would appear farther south. The orientation of the pictures is with the ecliptic (the plane of Earth’s motion) horizontal. Thus the northern hemisphere of the Earth tilts toward the Sun in (northern) summer, away in winter. The Moon-inhabitant sees the Earth apparently moving backward (to the left or east): it is really traveling forward, but the Moon, at the full-Moon stage of its orbit, is overtaking the

eclipses would be incomplete without them.” Having come to the ascending node almost too early for an eclipse on April 25, the May full Moon now passes the same node almost too late. That is, 28 hours after the Moon climbs through the ecliptic plane, Earth’s shadow passes mostly south of it. Gamma in this case is 1.535—more than 1½ times the Earth’s radius from the center of the shadow; practically at the very limit where it can still make contact (however slight) with the penumbra. This night’s full Moon, even though you won’t see the shadow’s touch on it, is worth gazing at for another reason. It is sailing among the four naked-eye stars of northwestern Scorpius, all of which are wide doubles. It occults Beta, as seen from the southeastern U.S., and then Nu, as seen from equatorial regions. And Omega, more than a degree south, happens at this time to mark almost exactly the anti-Sun, the direction to which Earth’s shadow is pointing. From this humble beginning, there will be 70 more eclipses belonging to saros 150, spanning a total of 1,262years. This saros contains 21 eclipses that are penumbral, while 38 will be partial and 12 will be total; the longest of these lasting 1 hour 45. 3 minutes (only about 2 minutes shy of the longest duration possible for a total lunar eclipse); this will occur on July 4, 2680. The very last member of saros 150 will be another very slight penumbral eclipse, this time at the southernmost limb of the Moon, on June 30, 3275.

IV. Oct. 18-19—Penumbral Eclipse of the Moon This begins the year’s second eclipse season, which unlike the first contains only two eclipses instead of three and is unsymmetrical: the opening lunar eclipse is rather far before

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Earth on the outside. He also sees the Sun’s path slanting to the ecliptic at about 5° because that is the angle at which the Moon itself is cutting across the ecliptic. Around the Earth appears a thin ring of light refracted and reddened by the atmosphere. The practical purpose of the diagrams is to show which parts of the Earth can see the eclipse: all those on the side facing the Moon. In each diagram, lands on the right are about to move out of sight: for them the Moon is setting and the Sun is about to rise at the same time. Lands on the left have just come into view of the Moon at the end of their day. Places that appear in all three pictures see the whole course of the eclipse.

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Astronomical Calendar 2013

the center, almost misses being an eclipse; the solar one comes shortly after the middle of the season and so is a more central eclipse. The Moon, aiming toward a descending mode more than 21 hours after the full Moon moment, again misses the center of the Earth’s shadow by a wide margin (gamma is 1.151—more than a whole Earth-radius). For nearly four hours at least some part of the southern portion of the Moon is within the pale penumbra; however, penumbral eclipses are rather subtle events which are usually difficult to detect unless at least 70 percent of the Moon’s diam-

The solar eclipses II. May 9-10—Annular Eclipse of the Sun (Australia, New Guinea, Solomon Islands, Kiribati, Tabuaeran) With the full Moon of April 25 dipping only slightly into the Earth’s umbra to create a partial eclipse, it then spends the next two weeks sweeping around to the opposite side of its orbit, to pass between us and the Sun at the New Moon position on May 9. But because it descends through the ecliptic only a few hours before (at 19:13 UT), this is near enough that its whole shadow will wipe across the center and south of the Earth. At 21:25 UT the surface of the cone of the penumbra, the outer shadow, meets the advancing chin of the Earth over the Northern Territory of Australia, a bit to the east of the small settlement of Newcastle Waters. Here, where the calendar reads May 10, a partial eclipse will be seen at dawn as a very slight indentation at the top edge of the rising Sun. Within the next 35 minutes the penumbra has rapidly spread northeastward, enveloping the eastern half of Australia, much of New Guinea and two of the three major geographical divisions (Visayas and Mindanao) of the Philippines. At 22:31 UT, the central part of the shadow strikes the Earth in the Pilbara Region of Western Australia on the east side of Collier Range National Park. The nearest major town is Newman, a modern mining community of about 4,200, 103 mi (166 km) to the north of the park and just inside the northern limit of the annular eclipse path. Australia Western Standard Time reads 6:31 a.m. on May 10 and given clear skies a most unusual sunrise will take place. The Sun will emerge into view from beyond the east-northeast horizon, first resembling a pair of lobster claws, and then when in full view, a horseshoe with upturned pointed tips. Finally, with the dark disk of the Moon appearing to move down as opposed to the Sun moving up, an offcentered “ring of fire” materializes, sitting just above the horizon. This wonderfully weird effect lasts 109 seconds, ending when the ring appears to “break” at the Sun’s lower limb. Within minutes the Sun again resembles a horseshoe, but now the pointed tips are directed downward. Because the Earth has been turning eastward in the 66 minutes since the arrival of the penumbra, the touchdown of the central part of the shadow ends up about 620 mi (1,000 km) farther down to the southwest. This “central part of the shadow” is not as easy to describe as the umbra or tapering central cone of shadow in a total eclipse. In this case, the Moon is near the apogee of its orbit (which it reaches 3½-days later), so it’s considerably

eter is immersed. So perhaps only for some minutes centered on the time of greatest eclipse (23:50 UT) may the penumbra be marginally detectable over the Moon’s southernmost limb; for at that moment the penumbral magnitude will reach 0.765. Those living across the eastern half of North America may see some evidence of this faint penumbral shading soon after local moonrise on the evening of Oct. 18, while the Indian subcontinent and the western half of China may notice some vestige of faint shading before the Moon sets on the morning of Oct. 19. It is a delicate spectacle for eastern

South America, all of Europe and Africa as well as western Asia. At mid-eclipse, the Moon appears in the zenith from Ouagadougou, the capital of West Africa’s Burkina Faso. Also take note of the fact that the Moon looks somewhat smaller at this eclipse than at the April one; that is because it is 6½ days before reaching the apogee of its orbit, whereas in April it was 2 days before the perigee—its distance (from the center of the Earth) is now 239,672 mi (385,714 km), whereas in April it was 226,987 mi (365,300 km).

more distant than average (249,215 mi). As a consequence, the umbra falls fully 15,045 mi short of reaching the “fundamental plane,” defined as the plane that cuts through the center of the Earth. Instead, what reaches the surface is the antumbra, an imaginary inverted extension of the umbral shadow cone. Anyone within it sees all sides of the umbra reaching almost to the edge of the Sun, creating an annulus or ring of Sun that is visible around the dark silhouette of the Moon. Where it first contacts the Earth’s sunrise terminator, the path is 138 mi (222 km) wide and the annular phase on the center line lasts 4 minutes 10.6 seconds. The antumbra quickly travels northeast across parts of Western Australia, Northern Territory and Queensland. The eclipse track passes over wide stretches of rather sparsely populated regions including the Gibson and Tanami Deserts; the latter according to government commissions is “one of the most important biological areas to be found in Australia particularly as it provides refuge for several of Australia’s rare and endangered species.” Tennant Creek, a town of 3,200, is roughly midway between the center line of the annular eclipse track and the southern limit, and lies just to the south of the junction of two great highways, the Barkly and the Stuart, also known as the Overlander and Explorer’s Ways. The Overlander’s Way (Barkly Highway) retraces the original route of early stockmen who drove their cattle from Queensland through the grazing lands in the Northern Territory. The start of the annular phase comes at 22:35:43 UT and lasts 3 minutes 7 seconds. Also in this region live the Warumungu (or Warramunga), a group of Indigenous Australians, many of whom speak Kriol or the Pama-Nyungan language of Warumungu. Unfortunately, other towns of similar size are few and far between along the eclipse path. By far the largest population center is The Atherton Tablelands, whose inhabitants’ number around 12,000. At the Rockhampton Downs Airport, the annular eclipse will last 3 minutes 58 seconds, mid-eclipse occurring at 22:38 UT with the Sun standing 17° above the east-northeast horizon. Passing over the south end of the Gulf of Carpentaria, the center line of the eclipse path scores a direct hit on Mornington Island, the northernmost of 22 islands that form the Wellesley group. Annularity will last 4 minutes 35 seconds beginning at 22:39:36 UT, with the Sun 22° high. After coming back onshore in Queensland, amazingly, the eclipse track passes over the very same area that experienced a total solar eclipse less than six months ago (November 14, 2012)! Places that fortuitously find themselves within the paths of both eclipses include Kowanyama, Maramie, and Dixie. The center lines of the two eclipses

cross just northeast of Mitchell-Alice Rivers National Park. Embarking into the Coral Sea at Cape Melville, the antumbra touches the easternmost end of Papua New Guinea, the center line intersecting Basilaki Island of the Louisiade Archipelago in Milne Bay Province. For Pihigole, mid-eclipse is at 23:00 UT with the solar annulus lasting for 5 minutes. About 150 mi (240 km) to the northeast, the shadow passes over the island of Muyua whose topography is chiefly raised coral pinnacles covered by dense jungle growth. Continuing northeastward, the shadow slices across the Solomon Sea and through the Solomon Islands chain, interacting with the islands of Mono, Shortland, Fauro, Choiseul, Vella Lavella, Kolombangar, and Santa Isabel before heading out over the Pacific. But there are yet other landfalls to be made, including the Republic of Kiribati, an island nation in the central tropical Pacific Ocean. A number of atolls with settlements are within the annular track, including Tarawa, best known by outsiders for the World War II Battle of Tarawa in Nov. 1943 (the first American offensive in the critical central Pacific region; nearly 6,000 Japanese and Americans died on this tiny island in the fighting). Bikenibeu settlement is only 2 mi (3 km) northwest of the center line; the antumbra arrives here at 00:12:12 UT. The Sun is then 73.5° above the horizon, the path width has narrowed to 107 mi (172 km) and annularity lasts a full 6 minutes. The decrease in path width is a result of Earth’s curvature, which brings points in the path closer to the vertex of the umbra. However, the duration of the annular phase actually increases, because the rotation of Earth’s surface partly compensates for the shadow’s relative motion. About 175 mi (282 km) to the northeast, the instant of greatest eclipse is reached at 00:25:13.0 UT. At this point, the shadow axis passes closest to the Earth’s center. However, the maximum duration of annularity—6 minutes 04.4 seconds—happens at a point which the antumbra reaches about ten minutes later. The very last landfall for the antumbra is a spit of land known as Tabuaeran or Fanning Island, belonging to one of the Line Islands of the central Pacific, and part of Kiribati. Tabuaeran is one of the closest bits of land—900 mi (1,448 km)—to the Hawaiian Islands, and was possibly used as a stopover by the Polynesians who first settled Hawaii. Captain Edmund Fanning of the American ship Betsy was the first non-Polynesian to sight this atoll, on June 11, 1798. The track of annularity continues over water; the annular eclipse is last seen 3,162 mi (5,089 km) west of Punta Aguja, Peru, at sunset at 2:19 UT. And after another hour and six minutes the penumbra loses contact with the rear part of the Earth’s surface that is turning away into night.

Annular Solar Eclipse, May 9-10 May 7, 07:13:10—Middle of eclipse season: Sun at same longitude as ascending node. May 9, 00:35—Moon’s center reaches descending node through ecliptic. 21:25—Partial eclipse begins: first contact of Moon’s penumbral cone with Earth, at local sunrise. 22:34—Central Eclipse begins: first contact of axis of Moon’s shadow cone with Earth, at local sunrise. Annular eclipse begins slightly earlier, when leading edge of Moon’s antumbral cone (prolongation of umbra) meets Earth. May 10, 00:19—Conjunction of Moon and Sun in right ascension: Moon’s center passes exactly south of Sun’s as measured perpendicularly to Earth’s equator. Center of eclipse takes place at local apparent noon, with Sun and Moon on the meridian. 00:25—Greatest eclipse: axis of shadow passes nearest (-0.2695 Earthradius) south of center of Earth. The magnitude of the eclipse is 0.9544; that is, the Moon covers this fraction of the Sun’s diameter. 00:28—New Moon (conjunction of Moon with Sun in ecliptic longitude): Moon’s center is exactly south of Sun’s as measured perpendicularly to ecliptic. 02:15—Central eclipse ends: last contact of axis of Moon’s shadow with Earth, at local sunset. Annular eclipse ends slightly later, when trailing edge of Moon’s antumbra leaves Earth. 03:25—Partial eclipse ends: last contact of penumbra with Earth, at local sunset. May 13, 13:54—Moon at apogee. 252,168 mi (405,825 km). This is eclipse number 31 of the 70 in solar saros series 138 (1472 June 6 to 2716 July 11).

Local circumstances for May 9-10. All times are in the clock time of the region. In the time zone column, locations marked with * are observing Daylight Time, which we have already accounted for. For locations marked with ** the calendar date is May 9. Parentheses () around a time mean that maximum eclipse happens when the Sun is below the horizon; the time given is, instead, that of sunrise. For those locations, the eclipse magnitude is the value for sunrise. *** means the event happens below the horizon. time 1st max. last zone contact eclipse mag. alt. contact Honolulu** AHST 2:22 PM 3:47 PM .441 42.9° 5:00 PM Hilo** AHST 2:27 PM 3:52 PM .473 39.0° 5:05 PM Surabaya UT+7h *** 5:33 am .472 0.0° 6:31 am Jakarta UT+7h *** (5:53 am) .196 0.0° 6:25 am Cebu City UT+8h 6:22 am 6:50 am .070 19.5° 7:19 am Singapore UT+8h *** (6:55 am) .042 0.0° 7:09 am Darwin UT+9.5h 6:57 am 8:06 am .756 15.5° 9:28 am Alice Springs UT+9.5h *** 8:07 am .845 13.6° 9:30 am Cairns UT+10h 7:27 am 8:48 am .881 28.9° 10:27 am Port Moresby UT+10h 7:37 am 8:54 am .889 35.2° 10:37 am Melbourne UT+11h* 8:50 am 9:52 am .367 16.7° 12:02 PM Canberra UT+11h* 8:49 am 9:55 am .380 21.4° 12:09 PM Hobart UT+11h* 9:06 am 9:59 am .233 15.7° 11:56 am Auckland UT+13h* 12:06 PM 12:48 PM .077 35.0° 1:33 PM

Locations within the path of annularity. ***: event is below horizon. time 1st annularity last zone contact begins dur. alt. contact Newman UT+8h *** 6:31:32 am 1:49 0.0° 7:45 am Tennant Creek UT+9.5h 6:55 am 8:05:43 am 3:07 15.3° 9:32 am Atherton Tablelands UT+9.5h 6:55 am 8:06:02 am 3:58 16.5° 9:34 am Pihigole UT+10.5h 8:02 am 9:27:30 am 5:00 38.5° 11:18 am Bikenibeu UT+14h 12:15 PM 2:12:12 PM 6:00 73.5° 4:22 PM Tabuaeran UT+14h 1:55 PM 3:46:37 PM 4:36 40.8° 5:18 PM

Astronomical Calendar 2013 um

VIEWS OF THE EARTH as the Moon’s shadow crosses it. The viewpoint is 12 Earth-radii from the Earth’s center flight of the um (whereas the little pictures of the bra in 1 hour (rel Earth at lunar eclipses are from the ative to Eartj cemter) Moon at its distance of about 60 Earth-radii). So the Moon is about 5 Ar times farther back, along the shadow c t i c which it casts, and the Sun is about C i r c l e 400 times farther than that. The cone 60˚N of the penumbra or partial shadow E 0˚ spreads as it goes away from the 15 Moon. The cone of the umbra or total shadow tapers; on May 10 it ends 3.8 Earth-radii short of Earth’s central plane; on Nov. 3 it reaches to se al eclip within just 0.03 Earth-radii of the cenf parti o t i lim tral plane. Continuing it on May 10 is hern nort the antumbra, or cone from within T r which annular eclipse can be seen. 30˚N o p Phil i c i p pine The gray patch, faintest at its o f s C a outer edge, is the footprint of the n c e r penumbra at the time of the picture. rota H aw As it moves eastward it sweeps out t in 1 ion aii h the broad band within which partial our eclipse can at one time or another be seen. Pa mid pu The outlines of the umbra or a eclipse antumbra on the ground are shown at 0:30 1 10-minute intervals, and their envefirst con 0 e q 1:30 ct u a lope forms the track of annularity or of penumbta 23:30 t o ra--------------r ---------------totality. (On Nov. 13 the outlines are 23 2 ntact-----------------very small; near the beginning, at the 22:40 first cuom ra b of transition from annular to total, the width is zero.) A us trali The ecliptic is the plane in which a T r lie the “flight of the Earth” and “Sun op i c overhead” arrows. The umbra and o f Ca the “Sun overhead” arrow are travel30˚S p r i c o ing in opposite directions over the r n surface; when they pass at the same N e 30˚S meridian of longitude, mid eclipse Zeala w nd happens at local noon. If you comsouthern limit o pare “flight of the Earth in 1 minute” f par tial (just one protruding part of the ecli pse An arrow) and “flight of the umbra in 1 t a r c hour,” you will see that really, in relat i c C i r c l tion to the Sun, the Moon is moving e forward the same way as the Earth, but slightly slower.

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2013 May 10 0:00 UT

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-last contact -----------------------------------------------of penumbra

Meanwhile all the rest of Australia and Tasmania as well as most of New Zealand, save for a southern and eastern slice of the South Island, sees varying degrees of partial eclipse during the morning hours of May 10. A large swath of the Pacific Ocean also falls underneath the penumbral shadow, so that most of the islands that comprise what are known as Micronesia, Melanesia and Polynesia will also see varying degrees of a partial eclipse. Places to the west of the International Date Line will see it during the morning of May 10, while places to the east of the Date Line see it during the afternoon hours of May 9. Hawaii falls into this latter category; the 50th state will see the Moon reach almost halfway across the Sun’s diameter in the mid-to-late afternoon hours.

V. November 3—Hybrid (Annular-Total) Eclipse of the Sun (Gabon, The Congo, Democratic Republic of the Congo, Uganda, Kenya, Ethiopia, Somalia) Two weeks after the full Moon and lunar eclipse of Oct. 1819, the Moon sweeps around to the opposite side of our orbit, crossing, at new phase, the line between Earth and Sun. Only about 6 hours before doing so, it reaches its ascending node, where it slopes northward through the ecliptic plane. This is what makes an eclipse possible, and makes it fairly central. The Moon’s shadow sweeps across the Earth, mainly across the northern hemisphere, though far enough south to include the center and to have a northern limit—in other words, there is an interval of time (amounting to about an hour) when the shadow falls entirely on the Earth, with none of it spilling beyond into outer space. The quantity gamma) which describes the centrality of the eclipse is 0.3273 (a bit less central than on May 9-10 when it was 0.2695): that is, the axis of the shadow passes north of the Earth’s center by this fraction of the Earth’s radius (about 1,295 mi or 2,085 km). The solar eclipses of 2013 balance each other (with subtle differences). In May the Moon was moving through its descending node yet the geographical course of the eclipse was mainly northward, whereas now the Moon is ascending, yet at first glance the path looks as if it runs mostly south: the reason is the attitude in which the Earth is traveling—north pole tilting backward in the months around the March equinox, forward around the September equinox. May’s track reaches its center as it passes from continent to ocean; November’s as it passes from ocean to continent. And then there is the most important factor: distance. In May the

Saros and coming attractions Every eclipse belongs to a series of similar eclipses 18.030 years apart (the period called the saros). This is the 31st of the 70 eclipses in the series assigned the arbitrary number 138. Solar eclipses at the descending node gradually work their way northward across the Earth. After 2013, there are 26 more annular eclipses, and then on March 1, 2500, comes a hybrid (annular-total) eclipse. What follow thereafter will be three total eclipses. The final nine eclipses of this series will be partials, with the penumbral shadow progressively slipping more and more out into space over the north polar region until the very last (As for annular eclipses in other series, the next will

Moon was approaching apogee and nearly at its most distant. Now the Moon is approaching perigee (2.83 days later), so that it is near enough to completely block out the Sun. It is by no means the nearest possible, but at the midpoint of its track across the Earth it is near enough that the umbra reaches as far as the Earth’s central plane, and if it were a steel needle it would slice about 3,800 mi (6,100 km) into the planet, instead of piercing straight on through and sticking out into space beyond as at some eclipses. So its trace on the Earth’s surface is unusually narrow. But it is the very beginning of the eclipse track that makes this event extraordinary. As noted in the header, this is categorized as a “hybrid” or annular-total (“A-T”) eclipse. During the 21st century approximately 4.9 percent of all central solar eclipses—those in which the center of the umbra or antumbra touches the Earth—fall into this class. In most cases, an A-T eclipse starts as an annular eclipse because the tip of the umbra falls just short of making contact with the Earth; then it becomes total, because the roundness of the Earth reaches up and intercepts the shadow tip near the middle of the path, then finally it returns to annular toward the end of the path. But within the small class of A-T eclipses, Nov. 3 will be (as pointed out by Jean Meeus) an even more special case. It starts as annular, and undergoes the change to total after only 15 seconds! And then it remains total to the very end of its path. The last time this happened was on Nov. 20, 1854, and the next such case after 2013 will occur on Oct. 17, 2172. So at the very beginning of this eclipse track, the tip of our “umbra needle” is just tickling the surface of the Earth; in the act of changing from annular to total, it is, in effect, a

be on April 29, 2014. The central axis of the Moon’s shadow misses the Earth, but the outer edge of the antumbra manages to interact with the Earth’s surface, creating a very unusual “non-central antumbral” eclipse. The zone of visibility will be restricted to the uninhabited region of Wilkes Land in Antarctica. Of this eclipse, retired NASA astronomer Fred Espenak writes: “since non-central eclipses do not have a central line, you cannot quote a central line duration. The longest duration will occur along the Earth’s terminator, where the eclipse occurs at sunset. Atmospheric refraction, however, will play its largest role at this point of the eclipse, making accurate predictions impossible!”

total eclipse with zero duration, then ever-so-slightly more after the first 15 seconds of its interaction with our planet. And the circumstances of such a “grazing” eclipse, where the disk of the Moon exactly fits over the disk of the Sun, are in some ways more interesting than an eclipse with a much longer duration of totality, as we shall discuss in more detail a bit later. Interestingly, at the very end of the eclipse track the part of the umbra needle striking Earth is 0.7 mi (1.1 km) short of the tip and only 0.6 mi (1 km) thick. The imaginary needle’s tip has traveled almost exactly along the fundamental plane through Earth’s center. The central eclipse path is 8,345 mi (13,430 km) long but, because of its narrowness, embraces less than 0.1 percent of Earth’s entire surface area. The speed at which the umbra travels over the Earth’s surface is huge at the beginning and end of the eclipse path, where the surface is turned away; it slows greatly, to about 0.35 mi (0.56 km) per second or 1,258 mi (2,023 km) per hour at the midpoint of the path where the surface parallels it and it is traveling in the same direction. The width of the umbra’s footprint on the Earth’s surface, divided by its forward speed, determines the duration of totality. Because of the timing of the Moon’s arrival between Sun and Earth, a hemisphere centered on the South Atlantic Ocean almost midway between Brazil and Angola is facing sunward. The southern hemisphere is tilting toward the Sun as it is now mid-spring in this half of the world; around the periphery of our globe is the circle separating day from night; the outer surface of the great cone of the Moon’s shadow first strikes the Earth at sunrise in the North Atlantic Ocean, about 545 mi (875 km) southeast of Bermuda. Here, a sharp-eyed observer on a properly placed ship, equipped

Astronomical Calendar 2013

with a number 14 welders glass or Mylar filter, might see the Sun rise with an incipient dent in its upper edge, deepening as it ascends. The penumbra—or “almost-shadow,”—though it scarcely seems a shadow within which this defect to the Sun can be seen—spreads rapidly onto the globe. During a timeframe spanning almost 5½ hours, people from southern Greenland down through the Atlantic seaboard of North America and into the Caribbean to northern Ecuador, then going as far to the east as South Africa and Madagascar and up to the north across the middle of Saudi Arabia to the Caspian Sea, see varying degrees of a partial eclipse. Those in the Americas see it happen already in progress in the early morning—they’ll look eastward at the Sun climbing the sky; southern Europe and western Africa will see it around the midday hour, while for central and eastern Africa, Greece and Turkey it will happen in the afternoon as the Sun descends the western sky. Places near the northern and southern limits, Athens and Johannesburg for instance, hardly notice; but in a narrow strip that cuts through the center of Africa, from Gabon east-northeast to Somalia, the day will turn strangely dark. The penumbra has been deepening for just over an hour when the core of the Earth’s shadow arrives—a thousand or so miles back west on the surface, because the Earth has been turning for an hour (or, more precisely, north of west since the Earth has been turning northeastward as viewed from the Moon, while the Moon itself has risen slightly northward). As noted earlier, the vertex of the dark cone of the umbral shadow initially might barely miss the Earth, and then a quarter of a minute later it begins to just scrape the Earth’s surface. However, it all depends on whose calculations you rely on as to whether the umbra actually makes contact with the Earth at the very start of the eclipse track or just barely misses. Jean Meeus and retired NASA astronomer Fred Espenak, for instance, prefer to use a smaller value of “k”—which denotes the radius of the Moon expressed in units of Earth radii. In contrast, back in 1982, the International Astronomical Union General Assembly adopted a slightly larger value of k; really a mean or average value, about midway between the deepest valleys and the highest mountain tops of the Moon. It is this value that is routinely used by astronomers at the U.S. Naval Observatory for their eclipse predictions. When the IAU value of k (0.2725076) is used, as by the USNO, the Nov. 3 eclipse is total from start to finish; when the smaller value (0.272281), as by Meeus and Espenak, the result is a slightly shorter umbral cone, hence an annular-total eclipse and a slightly shorter duration of totality. The thinking is that the “valley” radius of the Moon should be used because when any sunlight is coming through the valleys at the Moon’s limb the eclipse is not total. For our Nov. 3 eclipse, the smaller value of k makes the Moon ever-so-slightly too small to completely cover the Sun at the very beginning, and I have decided to use this smaller lunar radius for our depiction of this eclipse in the Astronomical Calendar. And yet, whether the umbra touches the Earth’s surface at the very beginning of the eclipse track—or barely misses—is somewhat irrelevant. The spectacle that one might witness at, or a short distance downrange from, that particular spot in the Atlantic Ocean—probably measuring less than a mile or two in width—some 405 mi (650 km) southwest of Bermuda will be a truly amazing sight; probably best appreciated from a precisely positioned high-flying aircraft. At 11:05 UT, the Sun would appear to rise as the black center of a broken, glowing ring which would last, at most, perhaps several precious seconds. We actually have a record of a solar eclipse that was observed under somewhat similar conditions. On October 3, 1986, an ardent group of nine eclipse chasers witnessed a similar borderline total eclipse from a Cessna Citation II, flying at an altitude of 40,000 feet above the North Atlantic to the west of Iceland. According to astronomer Dr. Glenn Schneider (who wrote of his experience in the February 1987 issue of Sky & Telescope, in the final few seconds before maximum eclipse “an extended arc of pink chromospheric light enveloped the lunar limb everywhere except for the last sliver of direct sunlight.” Six seconds later, that last sliver broke into “a multitude of beads.” Within a few more seconds the ring of chromospheric light became whole, “punctuated by beads at the lower left edge of the Moon.” Two additional beads then broke out on the opposite side of the disk creating for a full six seconds, something akin to a diamond tiara! Notes Dr. Schneider: “the blinking dance of beads flashed along the limb, interrupting the pink chromospheric hoop surrounded by corona. It was six seconds that took an eternity and no time at all.” As a bonus, a minute later, the airborne eclipse watchers could watch the Moon’s shadow projected on the cloud tops “like a dark stain . . . a blob of spilled ink, shaped like a squashed cigar, speeding away from us toward the horizon.” One might wonder if a similar airborne attempt—perhaps originating from Bermuda or Puerto Rico—will be made by some intrepid eclipse watchers to view the Nov. 3 eclipse from near the sunrise point of the shadow path, in hopes of perhaps viewing a similar panoply of phenomena as described by Dr. Schneider.

Sweeping southeast, the path of totality will slowly widen and the duration of totality will gradually increase, although the shadow will remain out over open ocean for 165 minutes before making its first landfall, in Gabon. Along the way, the point of greatest eclipse is reached at 12:46:28 UT over the tropical eastern Atlantic, at a point 204 mi (328 km) southwest of Monrovia, the capital of Liberia. At maximum at midpath, totality lasts 1 minute 39.6 seconds and the path is 36 mi (57.5 km) wide. At 13:44 UT, the umbra passes roughly halfway between São Tomé and Príncipe, a Portuguese-speaking island nation in the Gulf of Guinea, and the island of Annobón Province also known as Pagalu or Pigalu. From the resort equatorial island of Ilhéu das Rolas (which belongs to São Tomé and Príncipe) the eclipse will become nearly total, with a magnitude of .995; by blocking off the remaining spot of sunlight with a finger, the Sun’s corona might briefly be glimpsed by some of the island’s 200 or so permanent residents. The umbra reaches mainland Africa at 13:50:21 UT, in the remote Wonga-Wongue Presidential Reserve, a tract of rain forest on the coast of the nation of Gabon. It was here in September 2008 that the highly rated American reality show Survivor: Gabon: Earth’s Last Eden debuted on the CBS Television Network. Survivor host Jeff Probst later noted: “I never knew Africa looked like this. We’ve done a season in Kenya, so that was my impression. But in retrospect, Kenya felt like going to the zoo compared to this; here we have wide-open green savannas, thick jungle, and yet we were sitting right on the coast. The animals here aren’t acclimatized to Range Rovers, so when you come across a family of elephants, it’s a big damn deal.” Here, on the center line, the total eclipse will last 1 min 08 sec, with the Sun standing 47º high in the southwest sky. the overall brightness is similar to 20 or maybe only 15 minutes before sunrise or after sunset. Not a few astronomy guidebooks have noted that during a total solar eclipse the level of the sky darkness is equivalent to that of a night illuminated by a full Moon; and indeed, the light of the corona does shine with intensity similar to the full Moon’s. However, because the totality path at the Gabon coast is so narrow—just 28 mi (46 km), on the center line at mid-totality—you would be at most no more than 14 mi (23 km) from the outer edge of the umbral shadow, so there will be a considerable amount of light filtering in from outside the umbra that will be evident all around the horizon and adding to the brightness of the sky. The third brightest star in the sky, yellow-orange Rigil Kentaurus (magnitude —0.3)—more popularly known as Alpha Centauri—shines 22° above the south-southwest horizon. The fourth brightest, orange Arcturus (—0.1), will be 41° high in the west-northwest; the fifth brightest, blue-white Vega, might be evident about 47° up in the north-northeast. But for such a short duration of totality, it might be more constructive not to waste time searching for stars, but rather to concentrate solely on the beautiful solar corona which appears to the unaided eye as a small halo of soft, pearly light surrounding the black disk of the Moon. By all means try examining it with binoculars during these precious seconds; if indeed we are at or near sunspot maximum in 2013 as some forecasts suggest, the corona may be brighter, larger and more imposing than usual, displaying a variety of broad and narrow rays. Arching over the Sun’s north and south poles you may catch a glimpse of intensified lines of light—called polar brushes—which follow the lines of the Sun’s tremendous magnetic force. And look especially along the dark edge of the Moon for solar prominences, appearing as jets of reddish orange or electric pink along the curve, lacing into the bright inner corona. Meanwhile to the north, the capital of Gabon, Libreville (pop. 578,000), lies outside the totality path and will experience a sort of eerie “counterfeit twilight” for a minute or two centered on 13:50:43 UT (2:50:43 p.m. West Africa Time) as the partial eclipse reaches a maximum of .981. During the next 37 minutes, the path continues out across equatorial Africa as its width and central duration again dwindle. Sliding east-northeast, it will cut through six more African nations. First is The Congo; then, the Democratic Republic of the Congo (known between 1971 and 1997 as the Republic of Zaire). This is the largest country on the eclipse path, and it has several cities with populations greater than 50,000 that are not far outside the path. One, Mbandake, the capital of the Equateur District, lies right on the southern limit of the path (the Résidence du Gouverneur de l’Equateur which overlooks the Congo River is just inside the path and will witness 15 seconds of totality beginning at 14:07:50 UT; meanwhile, the Airport is just outside and will see an extremely tantalizing partial eclipse, with a magnitude of .999). But although an estimated 729,000 people live in Mbandake, years of war and neglect have taken a heavy toll on this city’s infrastructure, with no electricity or running water in large sectors of the city. Most of the streets and avenues are little more than dirt roads. The path then cuts across a small slice of sparsely populated northern Uganda and northern Kenya. Nearing its end, it crosses into southern Ethiopia. During this trek across the center of Africa the Moon’s umbra manages to bypass several huge population centers, meaning that tens of millions of people all must settle for consolation prizes consisting of mere partial eclipses, albeit all with fairly large magnitudes. Among them are Kinshasa (.875 at 14:05 UT), Kampala (.926

at 14:24 UT), Addis Ababa (.864 at 14:24 UT) and Nairobi (.845 at 14:27 UT). Finally, just before the umbra leaves the Earth at sunset over west-central Somalia at 14:27 UT, an exceedingly short total phase predicted to last for less than a second (!) might be seen from a point roughly midway between the cities of Galinsoor and Galkacyo, the latter being the capital of the North Central Mudug region, which boasts a population of 545,000 and could witness a sunset (at 14:27 UT) with all but one-half of a percent of the Sun’s diameter covered by the Moon. As was the case at the sunrise part of the path three hours and 22 minutes earlier, fortuitous observers who might have access to a clear horizon toward the west-southwest might witness the setting Sun again taking on the appearance of, in the words of Dr. Glenn Schneider, “a diamond tiara.” But it should also be stressed that Somalia is extremely dangerous for independent travel or sightseeing due to the ongoing armed conflict between Government forces and Islamist insurgents, kidnappings, warlording, and piracy. In short: eclipse or no, the easiest method for staying safe in Somalia is not to go there! Weather prospects For the first two and three-quarter hours of the umbra’s contact with our planet, it is passing over water. Between the sunrise point (longitude 71º W) and longitude 35ºW, satellite data indicate a mean cloud cover between 60 and 70 percent. But with access to satellite imagery and weather outlooks that are driven by good computer guidance (and with a knowledgeable meteorologist who can properly interpret this information), a cruise ship with adequate mobility can at least try to improve on those pessimistic odds of getting a view of the Sun on eclipse morning. As one progresses south and east from 35ºW, the average cloud coverage increases, unfortunately reaching as high as 80 to 90 percent near the point of greatest eclipse. Cloudiness then quickly decreases back to 60 to 70 percent for that part of the track that passes over the ocean south of the Republic of Côte d’Ivoire (or Ivory Coast). The obvious advantages of placing a vessel here to observe the eclipse, as opposed to near the beginning of the eclipse track, is a longer duration of totality and a higher altitude of the Sun above the horizon. The disadvantage is that this climatologically favorable region only spans about 10º in longitude (centered on 5º W); average cloudiness rapidly increases as one heads east-southeast, again reaching 80 to 90 percent near the coast of Gabon. Though there is more maneuverability in that similarly favorable zone for less cloudiness during the early stages of the eclipse track, the drawbacks are a shorter duration of totality as well as a lower Sun angle. CAN THAT RATHER LONG AND TANGLED PARAGRAPH BE BROKEN IN TWO? As for the western half of the African part of the track, it can be summed up in one word: grim. During November, the Intertropical Convergence Zone—a breeding ground for convective cloudiness and heavy, showery tropical rains— passes directly across Gabon, The Congo and the Democratic Republic of the Congo. At Lambarene, Gabon, for instance, November is right in the middle of the wet season, with 15 inches of rain typically falling during the month. Other factors include the greater daytime heating of land surfaces compared to water, and a general increase in humidity as a result of the transpiration of water vapor by surrounding jungle vegetation. It makes this particular region “one of the cloudiest on the globe at this time of year” according to Canadian meteorologist Jay Anderson, who specializes in eclipse climatology. Still, in the words of the late Robert A. Heinlein, one of the most popular, influential, and controversial authors of science fiction in the 20th century: “Climate is what you expect, weather is what you get.” And Anderson seems to agree, at least regarding eclipse weather across western Africa: “the weather is much more variable than the climatology. Invariably, some areas with high average levels of cloudiness will be sunny on eclipse day, and some with good climatological prospects will be cloudy.” So in spite of the poor statistical averages, there’s a glimmer of hope! As one continues east-northeast into Uganda, Kenya and Ethiopia, some good news: the atmosphere dries out noticeably; we enter a more arid climate. Precipitation and cloudiness gradually diminish and the probability of getting a clear view increases. Probably the best ground-based location to view totality is in the vicinity of Lake Turkana in Kenya. Lodwar (pop. 17,000) is the largest town in northwest Kenya but is situated outside the eclipse path. The center line of the eclipse is a 60 km drive to the northeast on the LodwarLokichogio highway up to the western side of the lake. The Lake is a large enough body of water to have a significant effect on the local climate by squelching convective cloudiness and precipitation. Slightly more favorable viewing conditions might be found on the eastern side of the lake, since you would be looking out over the lake and toward the eclipsed Sun. Sibiloi National Park is here, lying on the northeastern shore of Lake Turkana, and the south perimeter of the park is within the totality path. There also is located (a few kilometers north of center line) the park headquarters of the Kenya Wildlife Service, the administering authority; camping and short-stay facilities for visitors; and the Koobi Fora Museum. But according to Jay Anderson: “the overland route to

Astronomical Calendar 2013

i c c t Ar 60˚N

nort

hern

nd reenla

l e r c C i

2013 Nov. 3 13:00 UT ey

Turk

limit o f partial eclipse 0˚

14:20 11:30 13:30

dor

n o r i c r p C a

o f

artial limit of p

surface of the pen umbra

last contact 4:14 PM 4:20 PM 4:22 PM 6:27 PM *** ***

umbra

sun overhead

alt. 47.0° 37.9° 34.2° 16.4° 12.3° 11.8°

eclip

0˚ 0

30˚S

dur. 0:55 0:49 Edge 0:20 0:06 0:14

th Sou a c r f A i

southern

totality begins 2:50:19 PM 3:03:06 PM 3:07:56 PM 5:22:54 PM 5:25:04 PM 5:25:10 PM

DR o g Con

r t o u a e q

i c o p T r

Saros and coming attractions This eclipse is the 23rd of solar saros series 143 that started with ten partial eclipses, the first on March 7, 1617, over eastern Greenland. These were followed by 12 total eclipses including those of September 10, 1923, and October 2, 1959, both of which passed over parts of the contiguous United States. In 1923, the totality path brushed the coast of southern California, barely missing Los Angeles but encompassing San Diego. In 1959, the sunrise point of the eclipse path touched the Earth near the border of southern New Hampshire and northeastern Massachusettsincluding Boston. Unfortunately, the remnants of Hurricane Gracie spoiled the view by cloaking much of New England with low clouds, mist and drizzle. On October 12, 1977, the path of totality encountered two passenger cruise ships positioned within a mile of each other in the Pacific Ocean (the Fairwind and Fairsea), then, near sunset, the umbra swept across the South American nations of Colombia and Venezuela where many die-hard eclipse observers were frustrated by clouds. 2013’s borderline eclipse—mostly total, annular for a few seconds—will be followed by three annular-total eclipses of more usual kind; then on December 16, 2085, by the first of 26 annular eclipses. Then come 20 partial eclipses, gradually diminishing in magnitude; the last occurring on April 23, 2897 over the South Pacific Ocean, as the cycle of 72 solar eclipses comes to an end. The next total solar eclipse will be on March 20, 2015; its track will fall primarily over open waters of the North Atlantic, beginning off the southern tip of Greenland, then sweeping northeast between Iceland and the British Isles before passing over the Danish-owned Faeroe Islands and the sparsely inhabited Norwegian island group known as Svalbard. The width of the umbral shadow will be unusually wide— 300 mi (485 km)—and the maximum duration of totality will be 2 minutes 47 seconds. Jean Meeus points out that even though the path of totality falls just short of reaching the North Pole, thanks to atmospheric refraction, totality will be visible there; the Sun will be sitting on the horizon during the 1 minute 58 seconds that its disk will be completely obscured by the passing New Moon.

on Gab

12:30 13 mid eclipse

ct st conta ----------f--plaenumbra -------o -----flight of the Earth in 1 minute <-------------------------Madagasca

ion rotat our in 1 h

the Park is laborious and accommodation is available for only a very few people—four to six, in fact.” Nonetheless, probabilities for a successful view of the totally eclipsed Sun in and around the Lake and points east toward Ethiopia are in the 60 to 80 percent range; probably the best for any region along the eclipse track.

Locations within the path of totality. time 1st zone contact Gongoue, Gabon UT+1h 1:12 PM Makoua, Congo UT+1h 1:31 PM Mbandaka UT+1h 1:38 PM Gulu, Uganda UT+3h 4:07 PM Kalokol, Kenya UT+3h 4:12 PM Siboli Nat.Park(HQ) UT+3h 4:13 PM

Somalia

11:10

Congo

first contact of penumbra-------------------------------

30˚N

-last conta

pia ---------------- of umbra

Ethio Uganda

Ber

o f

˚E

----------

i c o p T r

0˚

a mud

60˚ W

30˚W 30

first con of umbtact ra--------

e r n c Ca

Ecua

Hybrid (Annular-Total) Solar Eclipse, November 3 Oct. 30, 19:46:43—Middle of eclipse season: Sun at same longitude as ascending node. Nov. 3, 06:54—Moon’s center reaches ascending node through ecliptic. 10:04—Partial eclipse begins: first contact of Moon’s penumbral cone with Earth, at local sunrise. 11:05:21—Central Eclipse begins: first contact of axis of Moon’s antumbra shadow cone with Earth, at local sunrise. Annular eclipse begins slightly earlier, when leading edge of Moon’s antumbral cone meets Earth. 11:05:36—Eclipse transitions from an annular to a total eclipse, as the vertex of the Moon’s umbral shadow makes contact with Earth. 12:38—Conjunction of Moon and Sun in right ascension: Moon’s center passes exactly north of Sun’s as measured perpendicularly to Earth’s equator. Center of eclipse takes place at local apparent noon, with Sun and Moon on the meridian. 12:46—Greatest eclipse: axis of shadow passes nearest (.3273 Earthradius) north of Earth’s center. The magnitude of the eclipse is 1.0159; that is, the Moon covers the Sun’s diameter and .0159 more. 12:50—New Moon (conjunction of Moon with Sun in ecliptic longitude): Moon’s center is exactly north of Sun’s as measured perpendicularly to the ecliptic. 14:27:41—Central eclipse ends: last contact of axis of Moon’s shadow with Earth, at local sunset. Total eclipse ends slightly later, when trailing edge of Moon’s umbra leaves Earth. 15:28—Partial eclipse ends: last contact of penumbra with Earth, at local sunset. Nov. 6, 09:14—Moon at perigee. 227,025 mi (365,361 km). This is eclipse number 23 of the 72 in solar saros series 143 (1617 March 7 to 2897 April 23).

c t i r c a t An

le r c C i

bra flight of the um to Eartj cemter) e iv at in 1 hour (rel

Local circumstances for Nov. 3. All times are in the clock time of the region. If maximum eclipse occurs when the Sun is below the horizon, the time of local sunrise is given in parentheses () or local sunset is given in double parentheses (()) instead; the eclipse will already be in progress at that time. For all such locations, the eclipse magnitude is the value at sunrise or sunset. *** means the event happens below the horizon. time 1st max. last zone contact eclipse mag. alt. contact Bogota UT-5h *** 6:06 am .196 5.2° 6:43 am Boston EST *** (6:20 am) .637 0.0° 7:12 am New York EST *** (6:28 am) .606 0.0° 7:11 am Miami EST *** (6:30 am) .506 0.0° 7:02 am Caracas UT-4.5h *** 6:31 am .439 10.2° 7:31 am Montreal EST *** (6:36 am) .468 0.0° 7:12 am Washington EST *** (6:37 am) .501 0.0° 7:09 am Pittsburgh EST *** (6:51 am) .289 0.0° 7:09 am Toronto EST *** (6:55 am) .236 0.0° 7:10 am Atlanta EST *** (6:58 am) .132 0.0° 7:06 am Cleveland EST *** (7:00 am) .153 0.0° 7:09 am San Juan AST *** 7:04 am .687 8.1° 8:08 am Hamilton AST *** 7:07 am .891 5.0° 8:13 am Halifax AST *** 7:16 am .542 2.7° 8:15 am St. Johns NST 7:01 am 7:53 am .384 9.0° 8:49 am Casablanca UT 11:29 am 12:29 PM .228 41.1° 1:30 PM Monrovia UT 11:03 am 12:46 PM .919 68.0° 2:28 PM Abidjan UT 11:24 am 1:09 PM .884 63.3° 2:46 PM Madrid UT+1h 1:00 PM 1:35 PM .078 33.8° 2:10 PM Ilhéu das Rolas UT 12:03 PM 1:44 PM .995 50.7° 3:10 PM Naples UT+1h 2:03 PM 2:18 PM .012 24.1° 2:29 PM Lagos UT+1h 12:48 PM 2:30 PM .813 53.1° 4:00 PM Libreville UT+1h 1:12 PM 2:50 PM .981 46.3° 4:14 PM Kinshasa UT+1h 1:34 PM 3:04 PM .874 39.1° 4:21 PM Athens UT+2h 3:07 PM 3:37 PM .070 17.8° 4:05 PM Cairo UT+2h 3:07 PM 3:58 PM .257 12.8° 4:45 PM Jerusalem UT+2h 3:12 PM 3:59 PM .240 8.7° 4:43 PM Johannesburg UT+2h 3:40 PM 4:16 PM .129 27.7° 4:49 PM Baghdad UT+3h 4:18 PM 5:03 PM .259 0.0° *** Teheran UT+3.5h 4:50 PM ((5:07 PM)) .141 0.0° *** Kampala UT+3h 4:09 PM 5:24 PM .926 16.6° 6:28 PM Addis-Ababa UT+3h 4:14 PM 5:24 PM .861 8.2° *** Lodwa UT+3h 4:12 PM 5:25 PM .990 12.6° *** Nairobi UT+3h 4:16 PM 5:26 PM .846 12.2° *** Gaalkacyo UT+3h 4:23 PM 5:27 PM .995 0.0° *** Dar es Salaam UT+3h 4:23 PM 5:28 PM .658 10.9° *** Dubai UT+4h 5:20 PM ((5:36 PM)) .203 0.0° ***

Capella

Astronomical Calendar 2013 ecliptic 180˚ 180 longitude

195˚ 195

+10 +10˚

165˚ 165

150˚ 150

+2 o

-1

Spic

Dec

Nov

Beeh ive

Oct

Sep

Aug

CAN CER

e q u a t o r

-15˚ -15

Jun

Jupiter

n Aldebara

TAUR

ORION

10 h

Plei

Jul

Mer Jul 28 cury

Jul 22

lus

-10 -10˚

75 75˚

GEMINI

Reg u

-5˚ -5

Castor Pollux

e c l i p t i c

90˚ 90

+30

105˚ 105

ad Hy

ecliptic latitude

2014

0˚

120˚ 120

LEO

VIR 5˚ +5

135˚ 135

M W i l a y k y

200 200˚ +15 +15˚

Coordinates of 2013 Proc yon MAP of Mars’s geocentric track against the starry background, ecliptic-based like the Mercury and Venus maps. The scale for this year is about 1.8 mm to 1°. The track is drawn in gray when Mars is in the morning sky (after conjunction with the Sun). Parts of the tracks for the neighboring years are included (in blue). Short blue lines connect Mars to other planets when they appear closest.

Betelgeuse

e s ma gn i t ud

5 4 3 2 1

--1

--2

--3

MARS

CA N C

Oct

asc node

I Sep

ec l i pt i c

eq sp M a r s Jun uin rin ox g Jul Aug De 200 c2 7 Nov 4 Dec

May

me a n

Apr

2005 Nov 7

di s t an c

Oct

t ua

Sun

Feb

C TI P LI EC

h Apr

perihelion

N LA

Aug

201 Jul 287 Jul

di s t a nc e

Sep 1 Aug 1

---

Jul 1

Jun 1 May 1 Apr 1 Mar 1 Feb 1

ial

----

Oct 1

r n u io ho at 2 t -ro in

tor equtah nor

n io --ct ---re n di Su to

Nov 1

RI C ORN

HELIOCENTRIC VIEW of the orbit of Mars. The view is as in the Mercury-Venus picture, but with the constellations removed from the front side of the sphere for clarity. A circle on the ecliptic plane shows the mean distance of Mars from the Sun (1.5237 a.u.). The planets are exaggerated 700 times in size. Dashed lines (each dash or gap 0.05 a.u. long) connect the positions of Earth and Mars at the dates of several successive oppositions. Mars’s winter solstice is (as for the Earth) when its north rotational pole is tilted most away from the Sun, and spring equinox is when the pole is tilted most backward. The equatorial plane of Mars makes a circle around the sky perpendicular to this pole, cutting its orbital plane in the directions of Mars’s equinoxes, which are roughly 90° from those of the Earth.

c i tp i l ce

---

CA P

mean dist. from sun 1.52 a.u. sidereal period 1.88 years = 687 days synodic period 2.13 years = 780 days eccentricity .093 inclination 1.9° diameter 6,790 km satellites 2

Jun

6 201 22 May

uq ro t a me a n

Dec 1

IU S

May

Feb

Mar

1 20

a rth r c nopola ---

Jan

ar 3 2012 M

2003 Aug 28

ecliptic north

Jan

n 29

Nov northernmost O latitude Dec

Mar

Sep 2010 Ja

al n r e v di

c t qui i o no n x

S P I S CE

M GE

Ma r nors rotat th p ion ole al

ecliptic north pole

ional rotat Earthorth pole n

AR I

R US T AU

A non-opposition year. Mars sinks in the sunset sky, disappears in March, from May, climbs slowly in the pre-dawn sky, and even by the end of the year has not quite started rising before midnight. Mars lies 1½ times farther out from the Sun than Earth, taking 1.88 of our years to complete an orbit. On our inside track, we take 2.13 years to catch up with Mars at each next opposition. Thus the oppositions are spaced around the sky roughly 1/7 of the circle apart, in a roughly 15-year cycle. Opposition years, like last, in which Mars makes a retrograde loop as we overtake it, usually alternate with non-opposition years like the present, in which Mars travels a longer and more distant path around the celestial sphere. After the 2012 March 3 opposition in Leo, Mars traveled nearly half way around the sky by the end of that year. This year it covers the other half and more: passes behind the Sun on April 18 at the PiscesAries boundary; visits Leo again in October-November; gets as far as Virgo, where next year it will slow into the loop centered on the next opposition, of 2014 April 8. At the start of 2013, Mars can be seen about 15° above the sunset horizon; it lowers and by March is gone. In early June it is a r te winlstice few degrees high at sunrise, though it will be hard to find till July, A QU o

Jan 1

THE DISK OF MARS at the beginning of each month. The scale is 1 millimeter to 1 second of arc. The diagrams are oriented so that the ecliptic plane (almost the same as the planet’s orbital plane) is horizontal. Short lines point to the north and south ecliptic poles; longer lines to the celestial poles. Direction to the Sun is shown by an imaginary stick, starting at the center of the planet (under the dot) and projecting one planet-radius beyond the surface.At Sun-conjunctions this line points almost straight toward us (almost exactly, since Mars is occulted behind the Sun). An arrow along Mars’s equator represents its rotation in 2 hours. In a year like this, the disk are small.

MARS AND SATELLITES at the beginning and end of this year; the rest of the time they are even s farther away and smaller. On Jan. 1 Mars, shrinking in apparent size, is in Capricornus and the Deimo outer Moon, 2 days past full, is in Leo; on Dec. 31 Mars, growing, is in Virgo and the Moon, 3 days 6 Jan 1 past last quarter, in Ophiuchus. Equatorial north is at top, to suit observation in telescopes; lines Phobor s 0 0h 1 12 inne point from the planet to equatorial north and south, shorter lines to ecliptic north and south. 6 2 3 Scale is 1 mm to 1 second. The satellites go around Mars in almost circular orbits and in planes 5 4 3 18 slightly varying from its equator. They are shown at hourly intervals, starting at 0h UT, which is 0h Jan 2 7 p.m. Eastern Standard Time or 4 p.m. Pacific Standard Time ON THE PREVIOUS CALENDAR DATE. The orbits are drawn thicker where the satellites are nearer to us than the center of the planet. Phobos goes around in only 7.65 hours, Deimos in 30.3 hours. Since Mars rotates in 24½ hours, Phobos travels more than three times faster than the planet’s surface: seen by a Martian, Deimos goes over slowly from east to west (more than 2 days from rising to setting), but Phobos goes in the opposite direction, rising in the west and setting in the east, twice a day! (Compare the arrow on Mars’s equator, representing rotation in 2 hours, with Phobos’s larger movement in half that time.) The satellites are exaggerated 30 times in size. Both are elongated: dimensions of Phobos are 27x22x19 kilometers, and Deimos 15x12x11 (as against the 6800 km diameter of Mars). Look closely and you will see that they are shown as ellipses. They rotate synchronously: that is, keep the same face to Mars. They are very faint: the magnitude of Mars is 1.2 on Jan, 1, 0.8 on Dec. 31, whereas Phobos and Deimos are about 13 and 14 magnitudes fainter.

2014 Jan 1 0h

Dec 31 0h 4 Deimos 5 outer 6 3 Phobos 2 inner

0h 1 Dec 31 12

l Algo

60 60˚

30 30˚

15˚ 15

0˚

345˚ 345

330 330˚

315 315˚

300 300˚ +15 h +15˚

20 CES PIS

ES ARI

Pleiades

the

Sun-conjunction Apr 18

Jun

o r a t u S e q ETU

ry rcu Meb 25

+10 +10˚ + 5˚ 5

Mercury Neptune Feb 8

Mar

-1

Jar

ranus

Venus

US TAUR

t cle Cir

ter Wa

Feb 4

Mars

RICO CAP

S RIU UA AQ

0˚

Jan

Mar U 22

Apr 7

Mercury

the

e c l i p t i c

May 8

S RNU

-5˚ -5 -10 -10˚

-2

- 30

-15˚ -15

Mira

Fom with orange Aldebaran higher to its right. On August mornings it slowly gains height as Jupiter and Pollux appear to move up past it, and Mercury struggles up from below. Seen gradually earlier and higher in the mornings of the rest of the year, it has little other notable company except for passing quite close above Regulus in October. It can be confusing (like many topics in astronomy where you have to juggle two ways of looking at things) that Mars travels fast around the map of the sky, as compared with the more distant planets; yet travels more slowly, in the sense of changing its position as seen by us. This is because the sky scene for us is based on the Sun, which is also moving across the sky map. Hence the characteristic low angle of Mars’s line in our Sun-centered ELONGATION graph. Look at it this way: when Mars “sinks only slowly” from evening to evening, it does so because it is striving harder than the more distant planets to stay ahead of the Sun; when it “climbs only slowly” in the pre-dawn sky, it does so because it is striving harder to keep up with the Sun.

ec l

pt i c

e c l

pt i

e c l i

Ur r t o ua eq

a rn ve

i qu

r di

ti ec

mag dia” 1.2 4.2 1.2 4.1 1.2 4.1 1.2 4.1 1.2 4.0 1.2 3.9 1.2 3.9 1.2 3.9 1.2 3.8 1.3 3.8 1.4 3.8 1.6 3.8 1.6 3.9 1.3 5.5 1.1 6.2 .8 6.9

n Aug 27 oppositio

s ar

1 C

s re

elo 24 19 16 15 12 8 6 3 0 -5 -9 -22 -24 -70 -81 -89

gedis 2.225 2.278 2.303 2.311 2.344 2.377 2.392 2.416 2.432 2.454 2.465 2.432 2.421 1.710 1.512 1.365

H alle y 1982

hedis 1.385 1.381 1.382 1.383 1.389 1.398 1.404 1.417 1.428 1.450 1.471 1.539 1.546 1.659 1.665 1.666

r.a.(2000)dec. 20 28 32 -20 14 perihelion 21 42 36 -14 52 .4ºS of Neptune 22 16 57 -11 45 .3ºS of Mercury 22 29 35 -10 31 4.2ºS of Mercury 23 16 38 -5 36 on equat.,to nor. 0 6 44 0 -3 .01ºN of Uranus 0 30 16 2 33 .7ºN of Venus 1 12 17 7 6 conjunc.with sun 1 44 31 10 23 .4ºN of Mercury 2 41 32 15 30 ascending node 3 32 22 19 7 max.declin.north 6 7 49 23 58 .8ºN of Jupiter 6 24 49 23 55 max.lat.north 11 39 5 4 13 ec l i sou. 12 19 34 on equat.,to 0 4 pt i c12 45 30 -2 31

0 9 16 21 22 11 18 16 1 22 8 11 6 23 2 0

3 ct

r ite

ut alha

TABLE OF PHENOMENA. For explanation see the MERCURY and VENUS section. Mars Jan 1 Jan 24 Feb 4 Feb 8 Feb 24 Mar 14 Mar 22 Apr 6 Apr 18 May 7 May 25 pt i c 16 Jul Jul 22 Nov 25 Dec 17 Jan 1

c pt i

1987 l e y Hal

opp o Aprsition 28

i c l

45 45˚

es ad Hy

baran

Astronomical Calendar 2013

IP L C E

Satu rn

HELIOCENTRIC VIEW of all the planets from Earth (smallest ellipse) outward. The whole orbits are shown in blue (with stalks to the ecliptic plane at yearly intervals); paths for this year in black (stalks monthly). Besides the major planets, we show a few minor bodies (of which there could be thousands in the picture): dwarf planet Pluto; asteroid 1 Ceres (as an example of the Main Belt of asteroids between Mars and Jupiter); and Comet 1P Halley, which at its last visit was first observed in 1982, and now, on the scale of the picture, is 18 cm (7 inches) from the Sun, approaching its 2023 aphelion. The viewpoint has receded to a distance of 100 astronomical units. The equatorial and ecliptic planes are represented by circles around the sky at a distance from the Sun of 35 a.u. Each dash or gap in the opposition lines is 0.5 a.u. long.

TI C

N PL A

E ro

opp osit ion

Rough guide to the constellations they’re in: Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Mars Cap Aqr Psc “ Ari Tau “ Gem Cnc Leo “ Vir

Jupiter Saturn Tau Lib “ “ “ “ “ “ “ “ “ Vir Gem “ “ “ “ Lib “ “ “ “ “ “

Uranus Psc “ Cet Psc “ “ “ “ “ Psc “ “

Neptune Aqr “ “ “ “ “ “ “ “ “ “ “

Jul

Pluto Sgr “ “ “ “ “ “ “ “ “ “ “

Plu

Astronomical Calendar 2013 Jup

ite

Mars

sta

n lio

rih

r ve

i equ

nox

ect di r

m a

rg o

opposition

e r c

Sun

lla

lion

rcur

r to ua

perihelion

Ve nu

tio

osi

p op

t i c i p l c

Ea rth

perihe

au t o r SPATIAL VIEW of a sphere 3.5 a.u. in radius, from a viewpoint 10.5 a.u. from the Sun. Grid-lines on the ecliptic plane are 1 a.u. apart. The path of each body is drawn for the whole year (Venus, 6 months; Mercury, 2 months). Stalks to the ecliptic plane show the body’s position at the start of each month. When it is at opposition, a dashed line connects its position to that of the Earth; each dash or gap is 0.1 a.u. long. Oppositions shown are in longitude (date of opposition in right ascension can be some days different). When an asteroid is in the morning sky (west of the Sun) as seen from the Earth, its course is drawn in gray.

ASTEROIDS

The age of asteroids (also called minor planets) began with the discovery from 1801 to 1807 of the four whose combinations of size and distance make them reliably observable every year. Then there was a gap of 38 years before others began to be found. Nowadays, discoveries (which receive provisional designations, though some are actually recovered objects) run at around 5,000-8,000 a year, and in 2012 the cumulative total of them passed 1,000,000. More than 300,000 have received permanent numbers (recognizing that they are separate objects whose orbits have been determined, so that they are unlikely to be lost); of these, more than 17,000 have received names. 1 Ceres was at opposition in December 2012, so we are now leaving it behind. Well north in March and April, even climbing along the southern fringe of Auriga, it sinks through the evening sky to pass behind the Sun in August. In September it reaches the perihelion of its 4.6-year orbit, but is by now more than 3 a.u. away from us and only 15° out in the sunrise sky. 4 Vesta was also at opposition last December, not far southwest of Ceres, so on its shorter and nearer-in orbit it

13h VENATICI12h

11h

1 -

10h

Arcturus

Sep Oct

+10 +10˚ Nov

Dec

Aug

Jun

1 Ceres Apr

GEMINI May

Sep Oct Sep Oct Sep Oct

15 26 13 27 12 29

oppos. perih. oppos. perih. oppos. perih.

gedis .809 .943 .811 .960 .814 .978

mag 8.1 9.2 8.1 9.2 8.1 9.3

Mar Apr

+30˚ +30

Feb

TAURUS

JanM ar F 4 Vesta eb Jan

Pleiades +20 +20˚

ec l i pt i c

Aldebaran Regulus

ORION

CANCER

Nov

Jun

Jul Aug

Sep

Spica

MONOCEROS

c De

i l ky

v No

Oct

+10 +10˚

Betelgeuse

Procyon

HYDRA

hedis 1.807 1.781 1.811 1.781 1.815 1.781

AURIGA

Sep

Oct

ra(2000)dec 23 15 6 21 22 54 8 55 23 10 5 16 22 50 8 8 23 05 4 12 22 46 7 24

The coincidence is getting less close, so was it closest for Palisa? No, he found it at a non-perihelic opposition, when it was as dim as magnitude 12. So all this does not really explain Capella why it wasn’t discovered earlier! At the beginning of this year, Bamberga is far off behind Algol 6h 5h 4h 3h 2h

Aug

VIRGO

-30˚ -30

1991 1991 2013 2013 2035 2035

Jul

t ic l ip c e

-20 -20˚

Bamberg in Bavaria, and the mayor, Dr. von Brandt, took the chance (in his welcoming speech?) to give his town’s name to Palisa’s asteroid. Its remarkableness results from three figures: size, nearness, and orbital eccentricity. Its diameter (determined by an occultation on 1987 Dec. 8) is exceeded only by the First Four and half a dozen others; and it comes closer to the Sun than any of the First Four. Yet it was one of the last large asteroids discovered, and the latest-discovered (except for 433 Eros, which we featured last year) that can become bright enough to be found with binoculars. But this happens rarely because in its very elliptical orbit (eccentricity 30°) it is far from us except at an opposition that happens when it is near perihelion; which has to wait for each 5th perihelion, or 22 years.

May Apr 2 Pall as

Rigel

Mira

CETUS

0˚

-10˚ -10

Sirius ERIDANUS -20˚ -20

Dec

-10 -10˚

May

Jun

LEO

Castor Pollux Jul

0˚

-U A

c i tp i l ce

+30˚ +30

+20˚ +20

ic t ip l ec

spends this year paralleling Ceres, which it will overtake early next year. Its relative nearness and light color keep it slightly brighter than the much larger Ceres, but fainter than the naked-eye visibility it just attains in opposition years. We passed 2 Pallas last year in September and will not overhaul it again till next February. It spends the year diving around the southern reach of its orbit (it is at southernmost latitude in August). The inclination of the orbit is unusually steep (35°) and is oriented not far from Earth’s equatorial plane and, awkwardly, almost along the line of sight in our spatial view! From Earth’s point of view, Pallas sinks behind the Sun in May before curving south. At perihelion in December, down in Hydra, it is well out in the morning sky for southern-hemisphere observers, at the same modest brightness it had last year at opposition. We passed 3 Juno last year in May, so now, it having progressed 73° around its orbit, we overtake it in August. This time it is markedly nearer in and more than a magnitude brighter. This is one of Juno’s better oppositions, though it can reach magnitude 7.5, as it will in November 2018. But it is outshone, as often happens, by one of the asteroids from lower down the list: For a non-First-Four asteroid, the clear choice this year is 324 Bamberga. It was discovered 1892 Feb. 25 at Vienna by Johann Palisa, who between 1874 and 1923 found 121 asteroids and comet C/1879 Q1. In September 1896 the meeting of the Astronomische Gesellschaft was held at

In contrast with last year, only one of the First Four—Juno, the poorest—is at opposition. But 324 Bamberga puts on its once-in-22-years performance, briefly outshining Vesta.

14h

-30˚ -30 Coordinates of 2000

c Astronomical Calendar 2013 right g ascension

40m +30˚

30m

20m

11 s Cere

1 +26˚

declination

11+24˚

e c l

Jul 1 1 1

Jun1

-4˚ -4

IC2087

50m 21h e q u a t o r

10m

20m

25m 0˚

-2˚ -2

1 b1 Fe

1 Ja1 Apr 1

4h40m

50m

Mar AURIGA 1 11 21 1 1

El Nath

+28˚

10m

i p t i c

CETUS b

+ 2˚ 2

p Se1

-20˚ -20

l k

a a.u. 2.77 2.77 2.67 2.36 2.69

Q a.u. 2.98 3.41 3.35 2.57 3.59

P years .08 4.60 .23 4.62 .26 4.36 .09 3.63 .34 4.40

PHENOMENA (for explanation see the

i ° 11 35 13 7 11

MERCURY

section).

1 Ceres Aug 18 5 conjunc.with sun Sep 13 20 perihelion

r.a.(2000)dec. 9 59 55 19 35 10 47 45 15 33

hedis 2.553 2.552

gedis elo 3.555 7 3.507 -15

mag 8.4 8.6

2 Pallas May 10 14 conjunc.with sun Dec 7 20 perihelion

3 32 25 -3 0 9 55 5 -20 51

2.414 2.130

3.326 21 1.796 -96

9.3 8.3

3 Juno Aug 6 17 OPPOSITION

the Sun; for the first seven months it slides north as it curves inward. After ascending through the ecliptic it suddenly in August, as we come around to face outward to it, seems to slow and fall back while still hurrying north. It is nearer to us than 1 a.u. from Aug. 5 to Nov. 1; when on Sep. 13 we look straight outward to it, it is only 0.81 a.u. away, nearer than any other large main-belt asteroid ever comes, and very slightly brighter than the twice-wider Vesta at this time. It will become a magnitude fainter by the time it reaches its actual perihelion, in late October, just after it appears to resume eastward motion.

near opposition). Stars are plotted from the Hipparcos catalogue. Projection is azimuthal-equidistant: angular directions and distances are true from the middle of the chart.

Aug 1

discov. diam. q km a.u. 1 Ceres 1801 952 2.55 2 Pallas 1802 524 2.13 3 Juno 1804 274 1.99 4 Vesta 1807 512 2.15 324 Bamberga 1892 228 1.78

PISCES e q u a t o r

previous day) is shown by a dot sized for brightness. The dots are gray when the asteroid is in the morning sky, white in the evening sky (into which the asteroid passes at or

name

Oct 1

0˚

Orbital and other facts. q: perihelion distance. a: mean distance. Q: aphelion distance. e: eccentricity. P: period. i: inclination.

No 1 v

Diphda

Homam Homama 50m 22h45m

let Circ e h t s isce P f o

Ja 1 n

a erg b m Ba 4 32 21

+ 6˚ 6

FINDER CHARTS on larger scale (0.75 cm per degree) for NGC24 asteroids around the 7times of their best visibility. Position at 0h UT of each day (7 p.m. Eastern Standard Time of the

23h

+ 8˚ 8

+ 4˚ 4

-18˚ -18

-16˚ -16

n z

10m1

20m

-14˚ -14

30m

M72

PEGASUS

2P alla s

Feb 1

40m

ma g n i t u d e s

5 6 7 8

45m ss21 Aldebaran +10˚ +10

open cluster

Dec

nebula

Saturn Nebula

NGC246

planetary nebula

NGC1647

10m

CAPRIC

e globular cluster

11-12 -12˚

20m

Markab

-10˚ -10

galaxy

f4 f3

30m NGC1817 NGC1807

Apr 1

i Co o r d i n a t e s o f 2 0 0 0 40m 50m

AQUARIUS 21

1 Jan1

TAURUS

+18˚

Ma1 y

ta 4 Ves

-8˚ -8

Feb 1

+20˚

AQUILA

1p Se

Crab Nebula z

Au 1 g

u kk12

Mar 1

+22˚

-10˚ -10

-6˚ -6

30m 20h25m

3J u

b NGC1746

40m

4 Vesta Jun 24 22 .4ºN of Venus Aug 9 11 conjunc.with sun Aug 20 4 1.4ºN of Mercury 324 Bamberga Sep 13 11 OPPOSITION Oct 27 9 perihelion

20 52 31

-4 48

2.667

1.668 168

8.9

7 55 7 9 20 46 9 40 38

22 48 18 25 17 3

2.481 2.444 2.434

3.384 3.456 3.438

23 3 -6

8.3 8.0 8.0

23 10 12 22 49 52

5 16 8 8

1.811 1.781

.811 170 .960 131

8.1 9.2

MAP for the selected asteroids through the year. Ticks are at 1st of each month; arrowheads at end of year. Paths are thicker where asteroids are brighter; gray where they are less than 15° from the Sun.

23h

18h 17h30m

+20˚ +20

Altair

ky i l

+10˚ +10

Wa y

Au g

the Circlle

19h M

Nov Sep

0˚

Jun

CETUS Jul

Mira Mar

2P alla s Jan

Jun

Dec

SERPENS

Jul

Ma y

Nov

Au g Apr Oct

3 Mar Juno Feb

SCUTUM -10˚ -10 Jan

(CAUDA)

Ma y

on po as Te

Apr CAPRICORNUS

Fomalhaut

0˚

AQUILA Sep

Feb

AQUARIUS

-20 -20˚

-30˚ -30

20h

Dec

+10 +10˚

-10 -10˚

21h

PEGASUS

Great Square

PISCES

22h

Oc t

+20 +20˚

SAGITTARIUS

ec l i p t i c

Mar 324 B Feb ambe r ga

-20˚ -20

the Teapot

Jan

-30˚ -30

For more information about asteroids: www.minorplanet.info/mpbdownloads.html (free online version of The Minor Planet Bulletin, which is no longer available in printed form except to some libraries and institutions); or Derald Nye at nye@kw-obsv.org.

Astronomical Calendar 2013

Dec 25 C /2 0 1

S 1

The planets are exaggerated 500 times in size, but the Sun is at scale. Lines on the ecliptic plane are 1 astronomical unit apart. IS

Vega

Oct

O N

LYRA

Jul

Mars

Dec

Nakkar

Nov

Oc t

Jan

Dec 23

No v Sulafa Shelyak t

Alkalurops

ES BOÖT

O 19 c t 65

1 S i 5 6 ek 9 S 1 a/ C ey Ik

Earth

CORONA BOREALIS

Keystone

STOP PRESS—Comet C/2012 S1 ISON

Pulche

v2 9

9 v2 No E e EN n r i s

w e st

On 2012 Sep. 21, just in time to complicate several parts of this intricate book when it was almost ready for printing, appeared a comet that could, in November and December 2013, become a daylight-brilliant immense-tailed The comet at and after periheSun-Grazer, to rival the few great ones of the past four centuries. lion. Scale 0.5 cm to 1 degree. It was discovered by Vitali Nevskiy and Artyom Novichonok, using a 16-inch The horizons move left (east) reflecting telescope belonging to ISON (the International Scientific Optical each day as the Sun does. The Gemma Network) in the observatory at Kislovodsk at the northern foot M ofaathe tail could be less or more strongsymCaucasus range in Russia. (ISON is, for an acronymic name, less distasteful than ly curved, and could be longer. 19 in PANSTARRS, but how a Comet Nevskiy would have delighted music-loversSarand Russian patriots.) It was in Cancer close to Gemini. More observations, and pre-discovery images found by others, enabled its orbit to be calculated. It was dimmer than magnitude 18, but more than 6 a.u. from the Sun—farther than Jupiter. When in January we look outward to it at opposition in Gemini, it will still Kornephoros be beyond Jupiter. We lose sight of it behind the Sun in July. In August and September, brightening (we hope) past magnitude 11, it may appear in amateur 17 telescopes, though low in the pre-dawn sky. At the end of September it crosses above the orbit of Mars; Mars happens to be there, so that on Oct. 1 they are only 0.07 a.u. apart. In October and November, now out as far as 50° into HERCULES our morning sky, Comet ISON races through Leo and Virgo at a rate increasing from 1° to 6° a day; its brightness increasing, if the forecasts hold, past any star, its tail trailing west. It crosses Earth’s orbit inward on Nov. 1; appears 2° north of Regulus on Oct. 16; dips on Nov. 9 into the short fraction of its orbit that is thi Rasalge hi south of the ecliptic; brushes only 0.38° north of Spica on the night of Nov. 15 17/18 (9 p.m. EST, 2 UT). Bright in the pre-dawn sky, it could begin to stay visCujam ible into the day, a decreasing distance west of the Sun. On Nov. 25, entering Rasalhague Libra and perhaps reaching the magnitude of Sirius, it bustles past (1.2° south of) one of its chief competitors this year, the slower and far dimmer Comet Encke. It catches the Sun in the northern panhandle of Scorpius, and at perihelion, late on Nov. 28, comet whips around star at a distance of only 0.012 a.u. from 13 the center (1,166,000 kilometers or 0.68 of a Sun-radius from the surface), hence at a speed of 190 km per second. Using what formulas we can for magnitude, we have it reaching —12.6, the brightness of the full Moon! So it just may be distinguishable (with care—masking the Sun out) like a lighted match at the Sun’s edge. For New Zealand dawn observers the growing tail may wash far out over Centaurus. At the dawn of Nov. 29 for North America, Comet 11 Celba i the Sun. Its tidal ordeal ISON should rise moments before and to the leftlraof may have wrenched it into fragments—which would add to the brightness. The tail will bend back down toward and perhaps under the horizon. Caution always: predicting the appearance of comets is guesswork, because SERPENS they are lumps of grit and ice which as they warm expel gas and dust—into the (CAPUT) sunlight-reflecting coma and tail—at times and quantities depending on their 9 structures and how they are spinning. So far it does not seem that ISON was in a misleading state of outburst when discovered, or has a composition like that which caused Kohoutek C/1973 E1 to be a relative disappointment. After the dramatic perihelion, we drive like a train toward ISON’s bridge, so see it racing straight north, each day more north and west of the Sun; at first only 7 low in the post-sunrise and pre-sunset skies, then rising rapidly earlier before 4 midnight. The tail slopes north over us so that we see its width as well as length; c e having had time to sprout outward but not to straighten, it gradually angles itself LIBR A D to get ahead, perhaps sweeping over the summer Milky Way. The Moon is full N º in Taurus on Dec. 17, at last quarter in Virgo on Dec. 25. From Dec. 27 the 0 comet is above our horizon all day and night, though lowest at 10 p.m. On Dec. 5 4 26 it crosses out over our orbit, but now we are there and it is almost vertically n o north of us (in the ecliptic sense), in Draco, at its nearest, 0.43 a.u., perhaps OPHIUCHUS z i down to magnitude 4. By the end of the year it is still climbing at more than 3° r a day, and will be north of us in the equatorial sense, passing within 4° of the o h north celestial pole on 2014 Jan. 7. still perhaps discernible to the naked eye. Dec 3 t See Astronomical Companion, COMETS, for a section on the Sun-Grazers. Of e s the eleven listed there, allSERP butENS one belong to the Kreutz group, chasing each n (CAU u other along one orbit, pieces ofDA) a proto-comet that broke up. Our comet’s orbit s is similar to that of the exception, C/1680 V1. Though 333 years and 20 days apart, they may constitute a second family; they have dropped from a region of Dec 1 the Oort Cloud just north of the direction of Castor, whereas the Kreutzers come from the direction of Sirius. All of the eleven except the first, C/1668 E1, grazed the Sun more closely than C/2012 S1 will. But it could be large. Sabikk The Kreutz sungrazer C/1843 D1, the Great March Comet, was brighter SCORPIUS than the full Moon. C/1882 R1, the Great September Comet, may have been even brighter. Brightest since then was Ikeya-Seki, C/1965 S1—overwhelmingly beautiful, a diagonal plume across the blue sky. Attach no superstition to its Jabbah “S1,” which merely means that it too was the first comet discovery in the secGraffias ond half of a September. (The system, imposed only in 1995, is Jan AB, Feb CD, Mar EF, Apr GH, May JK, Jun LM, Jul NO, Aug PQ, Sep RS, Oct TU, Nov VW, Sun Nov 29 Dec XY.) Ikeya-Seki was discovered only 33 days before perihelion—a sudden Nov 29 Nov 27 Dec 4 Dec 9 visitor compared with the 14 months warning that sophisticated instruDschubba Dec indeed 29 Dec 14 Dec 24 C/2012 S1. Dec 19 not bode bloody ments have given us for ISON It will revolution, as Indonesians thought the 1965 comet did; nor will a magic spacecraft follow it, as a suicidal cult believed of Hale-Bopp C/1995 O1. Nor is it certain to be as bright as the full Moon and bisect the sky with its tail. But it may. —Guy

y ilk

a W

Kaus Borealis

ARIUS

y lk

Antares

Zubeneshamali

Astronomical Calendar 2013

OCCULTATIONS

by Richard Nugent

An occultation happens when a solar-system body passes in front of a more distant one or a star, partially or totally hiding it, momentarily blocking its light. Each occultation can be seen only at the right time and from a limited part of the Earth. The most common such events are total occultations by the Moon, in which the Moon passes in front of a star, asteroid, planet or other object. Total occultations happen every night wherever the Moon can be seen. Practically, though, with small telescopes, only stars or planets brighter than magnitude 8.0 can be seen being occulted by the Moon’s dark limb and stars brighter than 3.5 on the bright (sunlit) limb. Four first-magnitude stars—Aldebaran, Antares, Regulus and Spica—lie within 5.5° of the ecliptic and are occulted by the Moon in 18.6-year cycles. These occultations can be seen with binoculars and small telescopes. In 2013 there are no occultations of Aldebaran, Antares or Regulus, but Spica is occulted 14 times. Other bright stars occulted by the Moon this year are Beta Scorpii (Acrab, magnitude +2.6) and Alpha Librae, (Zubenelgenubi, magnitude +2.8). The asteroids (3) Juno and (4) Vesta are each occulted by the Moon once in 2013, with visibility only over the South Altlantic and South Pacific Oceans. There are rare occasions in which a total occultation of a bright star or planet can be seen with the naked eye when the Moon is at crescent phase. For this to be possible, the altitude of the Moon must be favorable and the sky transparency excellent. A grazing occultation occurs when the Moon’s edge bare-

I Dec 1 Sep 8 Jan 22 Feb 18

ly glides by a star. Tbe star appears to blink as it disappears behind mountains and reappears through valleys on the Moon’s limb or edge. The graze line is a line on the Earth that projects the limb of the Moon from the direction of the star. The graze path can range in width from 500 meters to several kilometers. Observations of these grazing events, when made by a team of observers at intervals along a line perpendicular to the graze path, are scientifically useful, helping to determine the shape of the Moon’s limb. The recent Japanese satellite Kayguya has provided high resolution altitude data of the lunar topography. It has refined the grazing occultation observations made by ground based telescopes over the past 50 years. An asteroid passing in front of a star (i.e. eclipsing it) causes the star to disappear for an interval from a few seconds to a minute. An observer in the path of the occultation may not be able, and does not need, to see the asteroid before the occultation: he only needs to know the position of the star and be watching it. The fainter asteroid and brighter star seem to merge into a combined object, whose brightness drops as the asteroid moves in front of the star. The drop in brightness of a naked eye star should be observable to the naked eye and be spectacular in binoculars. If the asteroid is itself below visibility, then the star vanishes completely. Since asteroids (like the Moon) have no atmosphere, these disappearances are usually instantaneous. For giant stars, the disappearance and reappearance can last a few tenths of a second, thus allowing the diameter of the star to be derived. Asteroid occultations provide a unique opportunity for ground based observers to directly determine the sizes and shapes of these minor planets.

planet Moon phase visibility Mercury 1 d Japan (reappearance only) Venus 3 d Uruguay, Argentina, Chile Jupiter 24 d Europe, N America Jupiter 8 d Australia

II star Moon phase visibility Jan 5 Spica 22 d Australia, S Pacific Jan 23 Zeta Tau 11 d W Australia Feb 2 Spica 21 d Central and S Africa, Madagascar Mar 1 Spica 18 d Central America, S America Mar 28 Spica 16 d China, SE Asia, Australia Mar 30 Alpha Lib** 19 d S America Mar 31 Acrab* 19 d S USA, Mexico, S America Apr 25 Spica 15 d Southern Africa, Brazil Jun 18 Spica 10 d S Central Africa, Madagascar Aug 13 Alpha Lib** 7 d S America Sep 8 Spica 4 d Middle East, Europe, Western Asia Oct 5 Spica 2 d N America Nov 29 Spica 25 d N America Dec 27 Spica 17 d E Europe, W Asia Dec 28 Zeta Tau 18 d Hawaii * Acrab = Graffias = Beta Scorpii **Zubenelgenubi = Alpha Librae III Mar Apr Mar Jun Jul Sep Sep Sep Sep Oct Dec IV Jan Jan Jan Feb Feb Feb Feb Mar Mar Apr Apr May Jun Jun Jul Jul Aug Aug Sep Sep Sep Oct Oct Oct Dec Dec Dec

03 29 30 16 22 03 04 08 08 11 20

asteroid 729 Watsonia 1909 Alekhin 41 Daphne 20707 1999 WW4 5103 Divis 341 California 10386 Romulus 920 Rogeria 1465 Autonoma 2085 Henan 4455 Ruriko

star HIP 53417 HIP 78933 HIP 93026 HIP 66200 HIP 100027 HIP 20711 HIP 3419 HIP 20732 HIP 100064 HIP 154 HIP 110395

02 04 28 01 09 22 23 05 16 18 26 01 12 29 10 26 06 25 09 11 16 21 25 27 15 19 26

asteroid star 1637 Swings HIP 15241 3846 Hazel HIP 60595 3925 Tret’yakov HIP 45758 3918 Brel HIP 30586 564 Dudu HIP 33133 469 Argentina HIP 25363 3291 Dunlap HIP 62915 1508 Kemi HIP 19823 4124 Herriot HIP 90510 1702 Kalahari HIP 26964 2612 Kathryn HIP 34608 476 Hedwig HIP 105315 332 Siri HIP 84478 1043 Beate HIP 97499 238 Hypatia HIP 116004 576 Emanuela HIP 94645 302 Clarissa HIP 116060 224 Oceana HIP 17588 15161 2000 FQ48 HIP 111535 196 Philomela HIP 2038 2595 GudiachviliHIP 19718 313 Chaldaea HIP 47310 41 Daphne HIP 97157 5057 1987 DC6 HIP 29426 1254 Erfordia HIP 38601 916 America HIP 106938 733 Mocia HIP 17548

mag 4.3 3.9 4.8 4.9 4.2 4.3 2.0 4.7 3.6 4.4 3.8 mag 6.0 5.9 6.6 6.9 6.5 6.8 6.4 6.1 6.3 6.2 6.4 7.0 6.4 6.0 7.4 6.4 6.6 6.4 7.1 7.6 6.6 4.7 6.7 4.4 6.9 6.1 7.2

max.dur. 4.2 sec 5.5 sec 9.3 sec 3.5 sec 1.4 sec 1.1 sec 2.4 sec 1.8 sec 3.4 sec 2.8 sec 1.3 sec duration 8.1 sec 1.4 sec 1.4 sec 1.7 sec 4.7 sec 14.8 sec 2.8 sec 0.7 sec 0.9 sec 1.2 sec 1.0 sec 6.0 sec 4.0 sec 3.5 sec 29.2 sec 9.5 sec 8.0 sec 3.6 sec 3.5 sec 11.8 sec 3.3 sec 3.0 sec 9.0 sec 5.2 sec 6.0 sec 1.0 sec 8.0 sec

visibility path width (km) Middle east, Russia 52 Africa, Australia 19 SE Asia 210 SE Asia 25 Australia 14 Alaska 17 SE Asia 19 Brazil, Uruguay 25 Hawaii, British Columbia 19 Mexico, S. USA 18 N USA, Canada 35 visibility path width (km) N America, Scandanavia 44 Australia 21 Middle East, India, Australia 47 Middle East 11 India, China, Japan 50 N. and S. America 123 Africa 21 Newfoundland, W. Africa 18 Australia 21 NW USA 38 Florida, Caribbean 27 Malaysia, Sumatra 132 Mexico, Texas 43 Peru, Brazil, Africa 34 Mexico 169 New Zealand, Australia 87 Australia 34 China, Russia 54 Australia, NW USA 34 S America, Africa, Turkey 142 Japan, China 32 Japan, Russia, China 95 Russia 210 India, SE Asia, Australia 20 Africa, S Asia, China 51 N Africa, Europe 34 Baja Mexico, USA 97

The asteroid events for this year have been chosen on the basis of having small path errors and being visible over populated areas. Occultations have been used since the invention of the telescope to determine the Moon’s position, time, and the observer’s position at sea; to measure stellar diameters; to discover unseen stellar companions; and to determine the size and shape of asteroids. An improved knowledge of the Moon’s limb profile has led to the most accurate method for determining the diameter of the Sun during solar eclipses. Almost all people who make occultation observations have mobile capabilities, since occultation events are location-dependent. However, for any particular location on Earth quite a few occultations occur each year, so any permanent observatory can be outfitted with relatively inexpensive equipment to collect valuable data. An observer’s geographic position and ability to time an occultation event accurately can be more important than the equipment used.

Naked eye occultation events—Planets See Table I. Venus: Sep 8 by the 3-day old waxing crescent Moon. Night-time event visible over Uruguay, Argentina, Chile. Jupiter: Jan 22, Feb 18, See Table I for details and areas of visibility.

—Stars See Table II. Spica: Sep 8, a spectacular event by the 4-day crescent Moon, visible in Europe, Middle East and Western Asia. Oct 5, visible in North America, by the 2-day crescent Moon. Nov 29, by the waxing crescent Moon, over North America. Zeta Tau: Jan 23, by the 11-day old Moon, over western Australia. Dec 28, visible over Hawaii, by the 18-day Moon. Alpha Librae: Mar 30, visible over South America, by the 19-day Moon. Aug 13, again over South America, by the first quarter (7-day) Moon. Acrab (Graffias): Mar 31, visible over the southern USA, Mexico and South America, by the 19-day Moon.

—Asteroids See Table III. (“Duration” means the maximum disappearance along the central line of the path.) In 2013 there is a spectacular naked eye occultation, lasting up to 3.4 seconds, of a mag. 3.6 star by the asteroid 1465 Autonoma. This occurs on September 8 by Universal Time, but is visible in Hawaii at 9:01 PM on the evening of Sep. 7. Start watching at least 2-4 minutes before the scheduled time. Another excellent event is over Canada and the eastern USA on the evening of Feb 21. 469 Argentina occults the mag +6.8 star for up to 14.8 seconds in a 123-km wide path between 8:10 and 8:16 PM, depending on your latitude. This is a “must see” event in the early evening hours. Other “must see” events are: Jan 2, 1637 Swings; Jul 10, 238 Hypatia; Aug 6, 302 Clarissa; Dec 26, 733 Mocha. See Table III for details, path width and visibility. Due to slight uncertainties in stars’ positions and asteroids’ orbits, each path of visibility is subject to updates as the occultation approaches. Revised details can be found at the International Occultation Timing Association’s (IOTA) page http://www.asteroidoccultation.com, one month before the event. This website gives ground path maps and star charts, and Universal Time for each degree of longitude and latitude of the path. Stars in the tables are identified by their Hipparcos (HIP) catalog numbers.

Binocular/telescope events—Planets See Table I. For events after Full Moon phase (14 d), disappearance is on the Moon’s bright limb and reappearance on the dark limb.

—Stars See Table II. Again, for events with the Moon’s phase older than 14 d, disappearance is at the Moon’s bright limb, requiring a small telescope, but reappearance from the dark limb can be seen in binoculars.

—Asteroids See Table IV. These occultations of bright stars by asteroids are visible with binoculars and small telescopes. See http://www.asteroidoccultation.com for detailed star charts and updated path information one month before the event.

For more information on how to observe occultations, including the simple equipment needed for making valuable observations, visit the home page of the International Occultation Timing Association (IOTA): http://www.lunar-occultations.com/iota The International Occultation Timing Association has a free ebook on Occultations: http://www.poyntsource.com/IOTAmanual/index.htm Occult4, a program written by David Herald of Australia, was used for the predictions of the occultation events listed in Tables I-IV for 2013.

Astronomical Calendar 2013 Maps for selected occultations, showing areas of the Earth within which they are visible during darkness. Arrows point into Jan 5 Spica

the areas of visibilty; dashed lines are the limits beyond which visibility would be in twilight. Maps drawn by Richard Nugent. Jan 23 Zeta Tauri

Jan 22 Jupiter

Feb 18 Jupiter

Mar 1 Spica

Mar 31 Acrab

Feb 2 Spica

Mar 28 Spica

Apr 25 Spica

Mar 30 Alpha Librae

Jun 18 Spica

Sep 8 Autonoma occults Algedi

Aug 14 Alpha Librae

Sep 8 Spica On the evening of September 7, the asteroid 1465 Autonoma will occult the mag. 3.6 star Algedi (6 Cap) for up to 3.4 seconds across the Hawaiian Islands. The asteroid’s 19-km-wide shadow path crosses the islands just a few seconds before 7:01 UT (9:01 PM Hawaiian time). The solid lines indicate the predicted path, dashed lines indicate the limits of uncertainty in the path. Although the path prediction has a large error, updates to the path wil be posted on IOTA’s asteroid occultation website (see text) one month before the event. This event is definitely worth a look! Autonoma was discovered on March 20, 1938, by Arno Arthur Wachmann at Bergedorf in Germany. Wachmann discovered 3 asteroids and 3 comets.

Oct 5 Spica

Nov 29 Spica

2013 Sep. 8 15h Spica mag. 1.0 elong. 37˚ 37 E

2013 Sep. 8 21h Venus mag. -4.1 elong. 40˚ 40 E

Dec 27 Spica

2013 Oct. 5 22h Spica mag. 1.0 elong. 11˚ 11 E

2013 Nov. 2 7h Spica mag. 1.0 elong. 16˚ 16 W

Views toward Earth from the direction of a star or planet as the Moon passes between; its “shadow” is drawn at mid occultation (given in UT to the nearest hour) and an hour before and after. These shadows define the track on Earth within which the occultation is visible—but not exactly, because the turning of the Earth is not taken into account. (An arrow on the equator shows how much Earth rotates in two hours.) “Mag.” is the magnitude of the occulted body; “elong.,” its angular distance from the Sun.

Dec 28 Alpha Librae

Side-diagrams (with celestial north at top) show the phase of the Moon, with the occulted body passing behind it at intervals of 10 minutes over the same 2 hours, as seen from the center of Earth. From places north of Earth’s center, the Moon will appear farther south. Spica is occulted at every passage of the Moon this year; each time, the occultation path passes slightly farther north, the Moon’s phase gradually changes, and the Earth is caught at a different moment of its rotation. On Sep. 8, the Moon occults not only the fixed target of Spica but the moving target of Venus.

Astronomical Calendar 2013 noon by the amount called the “equation of time” (see the GLOSSARY). Orange curves show where sunset and sunrise would be for various latitudes. At a planet’s opposition it is up all night (roughly) and none of the day. Meteor showers are marked at the local times when their radiants are highest. Two thick vertical lines, displaced to the left in summer, represent 5 p.m. and 8 a.m. by the clock (for places on the meridian of their time zone). This shows how the purpose of setting clocks back from standard to “daylight-saving” time is to approximate to the earlier rising of the Sun. In summer we call the true 7 o’clock “8,” the true 12 “1,” etc.

really just one time-line, a cut and flattened helix. The dark zone down the middle is night, between the curves of sunset and sunrise. The three bordering gray bands are the times of civil, nautical, and astronomical twilight, when the Sun is less than 6°, 12°, and 18° below the horizon. Slanting lines show the hours of sidereal time: that is, which hour of right ascension is on the meridian. Thus 0h-1h sidereal time is the “Andromeda Hour,” when that gore of the sky is highest. Sidereal hours are 10 seconds shorter than clock (solar) hours and thus fall 4 minutes earlier each day. The times of the Sun’s transit across the meridian are shown by orange spots. This time differs from mean

RISING AND SETTING This hourglass shows times when the Sun, Moon, and planets rise and set, for latitude 40° north, longitude 0°. (They differ little for other longitudes, much more for other latitudes.) These are local mean times; to adjust them to your clock time, see the “Personal Reminder” on the preceding page. The lines representing days (actually drawn only for days 1, 6, 11, 16, 21, 26 of each month) begin at midnight, which is in the middle because we choose to show night rather than day undivided. Each day-line 2013 ends at the point where the next day starts, so there is local mean time

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Ursids

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5 p.m. clock time

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Geminids

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Alpha Monocerotids

Leonids

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Northern Taurids

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Europe

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Orionids

Europe

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Sun transits

Southern Taurids

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Uranus opposition

Mars

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Alpha Aurigids

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Sun transits

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Delta Aquarids

ris es

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Jup ite rs ets

Alpha Capricornids

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Mar s se ts

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Sun transits

July

Pluto opposition

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8 a.m. clock time (summer)

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Jup ite r

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June Bootids

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Eta Aquarids

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5 p.m. clock time (summer)

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sunset 20 N

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Saturn opposition

sunset at equator

set sun

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sunset 20 N

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sunset at equator

May

Lyrids

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June

N R O 2 2 IC R

Europe

August

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September

ris es

October

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USA

Venus sets

April

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November

culmina

December

9 10 11 12 1 Quadrantids

rise s

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full Moon rises

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full Moon culm

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8 a.m. clock time

5 p.m. clock time

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Sun transits

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first-quarter Moon cu

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new Moon sets

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February

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March

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January

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