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Moon, Saturn, Antares

October 16, 2015

Only one of the solar system’s planets is in easy view in the evening sky right now: golden Saturn. Tonight, it’s close to the lower right of the crescent Moon as night falls. The bright orange star Antares, the heart of the scorpion, is a bit farther to the lower left of the Moon. Saturn and Antares are fairly low in the sky, so you need a clear horizon to see them.

You won’t be able to see Saturn for much longer, though. The planet is dropping toward the Sun, and soon will become hidden in the Sun’s glare. It’ll pass behind the Sun at the end of November, then climb into view in the morning sky by Christmas.

Most of that motion is actually the result of Earth’s motion around the Sun. Saturn is almost 900 million miles from the Sun, so it takes the giant planet almost 30 years to complete a single orbit — far longer than any other bright planet. As a result, it doesn’t shift much against the background of stars from month to month or even year to year.

In those 30 years, though, Earth completes 30 orbits. As we swing around the Sun, our viewing angle on Saturn constantly changes, so the planet crosses from evening sky to morning sky once every 12-and-a-half months. It then hides in the Sun’s glare for a few weeks before once again climbing into view in the dawn twilight — beginning another year-long trip across the sky.

We’ll talk about a couple of small objects that are moving across the sky in a hurry tomorrow.


Script by Damond Benningfield, Copyright 2015

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