Moon and Regulus

No matter how unsettled our world gets, there’s one thing you can always count on: the clockwork precision of the heavens. Each star has its own season — a time when it shines at its best. And the Moon glides across the sky with its own predictable rhythm, passing by the same stars each month.

That rhythm is on display in the west as darkness falls the next couple of nights, as the Moon passes Regulus, the heart of the lion. It’s to the left or upper left of the Moon tonight, and to the lower right of the Moon tomorrow night.

The Moon passes closest to Regulus every 27 and a third days. That’s the Moon’s “sidereal” period — its cycle against the background of stars. But each time the two bodies pass, Regulus has moved farther westward in the sky.

That’s because Earth makes one turn on its axis relative to the stars in 23 hours and 56 minutes. Because we’re moving around the Sun, though, it takes a little longer for it to return to the same spot in the sky — 24 hours. Thanks to that difference, the other stars rise and set four minutes earlier each day.

So every star shifts a little farther westward every night. Regulus, for example, first appears in the dawn sky in early September. It stages its best appearances, when it’s in view all or most of the night, in spring. It disappears in the evening sky near the end of July.

And the Moon slips past it roughly every four weeks — a reassuring rhythm in the night sky.

Script by Damond Benningfield