Lunar Eclipses - Prof Kavan Ratnatunga

Total Lunar Eclipse Dr Kavan Ratnatunga Astronomer

Ecliptic plane

Moon’s orbital plane

• The Moon orbits the Earth at an angle with respect to the Earth’s orbit around the Sun • The Moon doesn’t shine on its own; it reflects sunlight • The scale of the Moon and Earth’s sizes and distance

Drawn to scale: scale Earth

Moon

Why Do Eclipses Occur The answer requires understanding the shadows.

Moon

Earth

Shadows > Umbra: Inner shadow > Penumbra: Outer shadow

•The shadow of the Earth can be divided into two distinctive parts: •The umbra and penumbra. Within the umbra, there is no direct solar radiation.

•As a result of the Sun’s large angular size, solar illumination is only partially blocked in the outer portion of the Earth’s shadow, which is given the name penumbra.

Why not a Eclipse every month ?

Moon Earth

5o Ecliptic Sun

Moon’s Orbit

Moon's orbit is tilted about 5o with respect to the Earth's orbit (ecliptic), so the shadows usually miss!

From the plane of Earth’s orbit . . .

5o

Earth’s shadow misses moon ⇒ no eclipse!

Orbit, viewed edge-on: s ’ n o Mo

e n a l p o r bi t

5o

Earth’s orbit plane At the nodes the Moon’s orbit crosses the Earths orbital Plane. If this happens at New Moon - Solar Eclipse Full Moon - Lunar Eclipse

Solar Eclipse Details

North Pole

Sun

Moon

What is the phase of the moon?

New Moon!

South Pole

Moon's shadow on Earth taken by French cosmonaut Jean-Pierre Haigneré aboard the Mir

A Lunar Eclipse

Sun A lunar eclipse occurs when the Earth lies between the Sun and Moon, so that Earth's shadow darkens the Moon.

Earth Moon

Moon’s Path

Lunar Eclipse • A lunar eclipse occurs when the moon passes behind the earth such that the earth blocks the sun’s rays from striking the moon.

• This occurs only when the Sun, Earth and Moon are aligned, with the Earth in the middle.

• Hence, it is always on full moon Poya night for a lunar eclipse.

• The type and length of an eclipse depend upon the Moon’s location relative to its orbital nodes.

• Unlike a solar eclipse, which can only be viewed from a certain relatively small area of the world, a lunar eclipse may be viewed from anywhere on the night side of the Earth.

Lunar Eclipse Types Total Penumbral Eclipse Total Lunar Eclipse Partial Lunar Eclipse Partial Penumbral Eclipse

Penumbral lunar eclipses • A penumbral eclipse occurs when the Moon passes through the Earth’s penumbra.

• The penumbra causes a subtle darkening of the Moon's surface.

• A total penumbral eclipse, when the Moon lies completely within the Earth’s penumbra.

• The portion of the Moon which is closest to the umbra can appear somewhat darker than the rest of the Moon.

Umbral Lunar eclipses • A partial lunar eclipse occurs when only a portion of the Moon enters the umbra.

• When the Moon travels completely into the Earth’s umbra, one observes a total lunar eclipse.

• The Moon’s speed through the shadow is about one kilometer per second (2,300 mph), • The total time between the Moon’s first and last contact with the Umbra could last up to 3.8 hours.

Moon at Perigee and Apogee Distance: 359,861 km

Distance: 405,948 km

Length of Lunar eclipses • The relative distance of the Moon from the Earth at the time of an eclipse can affect the eclipse’s duration.

• When the Moon is near its apogee, the farthest point from the Earth in its orbit, its orbital speed is the slowest.

• Thus, a totally-eclipsed Moon occurring near apogee will lengthen the duration of totality.

• Totality may last up to nearly 107 minutes.

The View from Earth

Duration: 77 min

This image shows a complete transition during a lunar eclipse. Notice that the phase of the moon is “full.”

Lunar Eclipse

Eclipse of Jan 20 – 21, 2000 “. . . the moon drenched with blood.”

The moon can becomes a blood red color during a long total lunar eclipse. No wonder that ancient cultures feared the appearance of the moon during a lunar eclipse.

Why is the Moon red during an eclipse?

• The Earth’s atmosphere refracts sunlight and allows it to reach the Moon’s surface • The blue light is removed—scattered down to make a blue sky over those in daylight • Remaining light is red or orange • A small fraction of refracted light reaches the Moon • Exact appearance depends on dust and clouds in the Earth’s atmosphere

Images from Fred Espenak http://www.mreclipse.com/LEphoto/LEgallery1/LEgallery1.html

What explains the red color ?

Earth’s shadow Sunlight

Moon

Earth

Atmosphere

• Atmosphere bends (refracts) sunlight into umbra • Atmosphere removes (scatters) blue/green part of light.

Danjon scale • The following scale was devised by André Danjon for rating the overall darkness of lunar eclipses: – L=0: Very dark eclipse. Moon almost invisible, especially at mid-totality.

– L=1: Dark Eclipse, gray or brownish in coloration. Details distinguishable only with difficulty.

– L=2: Deep red or rust-colored eclipse. Very dark central shadow, while outer edge of umbra is relatively bright.

– L=3: Brick-red eclipse. Umbral shadow usually has a bright or yellow rim.

– L=4: Very bright copper-red or orange eclipse. Umbral shadow is bluish and has a very bright rim.

Upcoming Lunar Eclipses

NASA Eclipse Home Page sunearth.gsfc.nasa.gov/eclipse/eclipse.html

2011 Jun 15 Total Eclipse of Moon

Contact Times in Sri Lanka • A very long Total Eclipse for which Lanka is perfectly located.

http://eclipse.gsfc.nasa.gov/OH/OHfigures/OH2011-Fig0 Umbral = 03h 39m 19s Total = 01h 40m 13s U1 = 23:52:55 LST 15th U2 = 00:52:29 LST 16th June 2011 U3 = 02:32:41 LST U4 = 03:32:14 LST

Viewing Conditions • The Totality on Poson Poya night is 100 min long.

• The longest for this Millenium was on 2000 July 16 which was 107 min.

• The last time Sri Lanka saw a 100 min Totality was in 1971.

• Should we make plans, maybe go out of Colombo to get away from bright city lights and the South West Monsoon.

Eclipses • Celestial bodies are always “eclipsing” or moving in front of each other.

• Other names include: Transits and Occultations.

• The occultation of 4.8-mag. 51 Ophiuchi (ZC 2523) will be spectacular in China, Taiwan, south-central Siberia, & s.e. Asia, and quite good across India and Sri Lanka.

• The brightest star occulted during this eclipse will be 4.8-mag. 51 Ophiuchi = ZC 2523 = SAO 185470. A map showing the region of visibility, and local predictions for hundreds of Asian cities, are on Rob Robinson's IOTA Web page for the occultation at http://www.lunaroccultations.com/iota/0615zc2523tot.htm .

• In the table of total occultation predictions, under the "CA" column, the occultation will be visible if a number (known as the umbral distance) and a "U" are under the "CA" (cusp angle) column; a value of 0 indicates that the occultation occurs at a part of the Moon at the center of the umbral shadow, while 100 is at the edge of the umbra. An "S" indicates that the event occurs against part of the Moon that is not in the umbra, and will thus be against the uneclipsed sunlit part of the Moon.

• As noted before, information about the spectacular grazing occultation of 51 Oph, visible in a narrow path crossing southern Thailand, central Cambodia, and central Vietnam, as well as many other grazing occultations of fainter stars, was posted on a Web page at http://www.asteroidoccultation.com/observations/le11615.htm • . The graze of 51 Oph will occur against parts of the Moon in the umbra east of longitude 78 deg. east, and will occur during totality east of long. 89 deg. east. Additional information about this rare lunar eclipse graze is at • http://www.lunar-occultations.com/iota/0615zc2523.htm , a Web page set up by Rob Robinson, including predicted Kaguya profiles for the event. West of longitude 78 deg. east, the graze will be against the uneclipsed sunlit limb of the Moon and very difficult or impossible to observe.

• David Dunham, dunham@starpower.net