Moon, Regulus, and Saturn

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The night sky is a series of continuously repeating cycles. The same stars roll into view at the same time each year. The Moon travels the same path every month. And the planets loop through the starry background in cycles that can last from months to decades.

That series of cycles is on display late tonight, in the form of the Moon, the planet Saturn, and the star Regulus. All three climb into view after midnight. Regulus is a little above the Moon as they rise, with Saturn following a good bit below them.

Regulus leads Leo, the lion, into the morning sky every fall, after the Sun scoots by the star in late August. Regulus rises about four minutes earlier each night, and moves into the evening sky in spring.

Because Earth "wobbles" a bit, though, the cycle undergoes a slow change. A couple of thousand years ago, Regulus climbed into view about a month earlier than it does now. And a couple of thousand years from now, it'll climb into view a month later.

The Moon circles through the stars every 27 and a third days, following the same path as the Sun. So it passes Regulus every four weeks.

Saturn circles through the stars, too, but at a much more leisurely pace -- it takes about three decades to complete a single circuit. It reverses direction across the sky as Earth pulls closest to the planet. Then it resumes its normal easterly path -- continuing a cycle that's been repeating for billions of years.

Script by Damond Benningfield, Copyright 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.