Mohawk valley astronomical society
give me a ring by carol higgins
Last month the big astronomy news was the close encounter of Jupiter and Saturn. It was a view not seen from Earth since the year 1226, and again in 1623 when astronomer Galileo was alive. Although the planets seemed to be next to each other, they were actually over 450 million miles apart. Each has unique features, but they share a trait that often goes unnoticed. They both have rings! But wait, there’s more! All four planets in our outer solar system have rings, and this month we take a look at those distant worlds: Jupiter, Saturn, Uranus, and Neptune. Without a doubt, Saturn is the king of the rings. A stunning sight through a telescope, reflected sunlight makes its huge rings shine so bright they can be seen with binoculars (a tripod helps). They are about 240,000 miles wide, the same distance between Earth and our Moon. Surprisingly they are only about 30 to 300 feet thick. Composed mainly of icy debris and rocks ranging from tiny particles to the size of a house, there are seven major rings containing hundreds of smaller bands. Gaps separate them, many created by the orbit of some of Saturn’s 82 moons. The most striking is the Cassini division, a region of empty space carved out by the moon Mimas. Next is Jupiter, a gas giant. Although it had been observed for thousands of
years, it wasn’t until March 1979 that we suspected it has rings. That’s when NASA’s Voyager 1 spacecraft flew by and took images with the planet The image shows Saturn and its rings (has the backlit by the Sun. Researchers dark Cassini division too, another Hubble shot). found compelling evidence of a Image Credit: NASA, ESA, Erich Karkoschka thin, faint ring that circled the planet. We finally got our best Image Credit: W. Keel, Galaxy Zoo gray, Team position. The NASA, innerESA, rings are dark up-close look when the Galileo Hanny’s Voorwerp. but the two outer rings are colorful; one spacecraft arrived in December 1995 to is reddish, the other bright blue. study Jupiter. It observed three rings, and Our final ringed planet is Neptune, ansince then we learned there are four. other ice giant. It has 14 moons, including The brightest is the Main Ring which one named Triton that blasts icy geysers begins about 30,000 miles above the into space. Five narrow rings contain upper atmosphere. The outer Gossamer small, dusty debris and some rocks, and rings extend almost 140,000 miles. But the mainly dark material makes the rings bright is a relative term. All are comprised difficult to see. One of the interesting of small bits of dark dust that researchers and unusual features in the outer ring are think were created when meteoroids imstructures called “ring arcs”. Scientists pacted four of Jupiter’s inner moons. The think they contain dusty material drawn rings cannot be seen from Earth. away from the ring by the gravitational Beyond Saturn is the ice giant Uranus forces of the moon Galatea, but they are and its 27 moons. Astronomer William at a loss to explain how they maintain Herschel discovered it in 1781, and a few their fixed shape and how they formed. years later he believed he detected some In our little corner of the universe, rings but could not support his theory. It none of the four inner planets have rings. wasn’t until 1977 that three researchers That special characteristic has been grantfrom Cornell University discovered five ed only to the giant planets far out in our rings. Two additional rings were found by cosmic neighborhood. We certainly have Voyager 2 in 1986, and the Hubble Space an interesting solar system. Telescope found two more in 2005. To Wishing you clear skies and good day we know of 13 rings, all thin in struchealth! • ture. They contain dark objects and dust, and astronomers aren’t sure of their com-
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