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See Saturn at its best in weekend's night sky


This diagram from a NASA video shows the alignment of Saturn, the Earth and the sun on April 28, 2013, when Saturn will be at opposition, making the ringed planet at its best and brightest of the year.

ByGeoff Gaherty

In the early hours of Sunday morning, the planet Saturn reaches opposition. This places it exactly opposite the sun in our sky.

Opposition has several effects on Saturn. Most important, it marks its arrival in the evening sky. It is now visible all night long, a treat for the many people who consider this the most beautiful object in the sky. On Saturday and Sunday night, Saturn can be found in the southeastern sky, weather permitting.

Saturn's opposition also marks the planet's maximum brightness for the year, and the brightest it has been for a number of years. At magnitude 0.2, the ringed planet now outshines the first magnitude star Spica in the constellation Virgo. Astronomers measure the brightness of night sky in terms of magnitude, with lower numbers denoting exceptional brightness. [Photos of Saturn's Dazzling Rings]

You can easily spot Saturn and Spica by following the old rule: "Arc to Arcturus, then speed on to Spica." Start by following the arc formed by the handle of the Big Dipper away from the Dipper's bowl in a broad arc across the sky, first reaching Arcturus in kite-shaped Boötes, and then on to Spica and Saturn in Virgo. Sparkling Spica is on the right, steady Saturn on the left. Starlight, coming from a distant point, is deflected by the Earth's atmosphere and twinkles. A planet like Saturn is larger than a star in apparent size, and so is less affected by atmospheric turbulence, so shines with a steady light.

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This sky map shows the location of Saturn in the southeastern night sky at 10 p.m. on Saturday to observers at mid-northern latitudes.

Saturn is most famous for its magnificent set of rings. All the outer planets have rings, but Saturn's are the brightest and most easily seen. Composed of small pieces of rock and ice, these rings are thin and transparent. When the rings pass in front of a star, the star's light shines through undiminished.

How much magnification do you need to see Saturn's rings? Although some people claim to have seen them with their unaided eyes, most people need a magnification of about 25 power to see that Saturn is an oval rather than a disk. For a really good view, 100 power is much better. Even so, Saturn appears much smaller in a telescope than most people expect. Although tiny, Saturn's perfection astounds all first-time viewers.

Besides its rings, Saturn has an amazing collection of moons, 62 in all. Its brightest moons are mostly in orbits in the same plane as the rings, as you can see in the chart. Its largest moon, Titan, is one of the two largest moons in the solar system; Jupiter's Ganymede is the other. These are the only two moons large enough to have extensive atmospheres. Titan is also the farthest object from Earth on which a spacecraft has landed, the unmanned Huygens probe in 2005.

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On Sunday morning, the planet Saturn reaches opposition close to the border between Virgo and Libra. Its brighter moons mostly appear to move in ovals in the same plane as its famous rings.

Titan can be seen easily in almost any telescope. Rhea, Tethys, and Dione can be seen with a 90mm telescope. The innermost moons, Mimas and Enceladus, are more challenging because the lie so close to the bright rings.

Iapetus is Saturn's most interesting moon. Its orbit is not in the plane of the rings, but is tilted at a steep angle. Like all large moons in the solar system, it always keeps one face turned toward its planet, but one side of Iapetus is coated with a dark sooty material. This results in Iapetus being much brighter when west of the planet than when it is to the east.

Because Saturn's moons can appear at any angle from the planet, you will need to use a planetarium software program to identify the individual moons and to distinguish them from background stars. Watching them change positions from night to night is fascinating.

Saturn holds something for every skywatcher. Everyone can enjoy spotting it in the sky, and those with telescopes can admire its rings and track the dance of its many moons.

Editor's Note:If you snap an amazing photo of Saturn and its rings and would like to share it with Space.com for a story or image gallery, please send comments and images to Managing Editor Tariq Malik at spacephotos@space.com.

This article was provided to Space.com by Starry Night Education, the leader in space science curriculum solutions. Follow Starry Night on Twitter @StarryNightEdu. Original article at Space.com.

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