Most of the time, the planet Venus is the brightest object in the night sky other than the Moon. Once or twice a year, though, it disappears in the Sun’s glare. And that’s what’s happening now. Venus is passing behind the Sun as seen from Earth, so it’s hidden from view.

This alignment is called superior conjunction. It happens about every 19 and a half months. Venus is farthest from Earth at that point — about 160 million miles away. So from our perspective, the planet moves across the sky quite slowly. As a result, it stays close to the Sun for several months — too close for us to see.

Superior conjunction is by the far the longer of Venus’s two vanishing spells. The other occurs at inferior conjunction, when Venus passes between Earth and the Sun. At that point, Venus is only about 25 million miles away — closer than any other planet ever gets. Because of the close range, Venus moves across the sky in a hurry, so it switches from the evening sky to the morning sky in just a few days — hardly enough time to even notice that it’s gone.

But after disappearing from the morning sky, it stays out of sight for much longer. This time, for example, it dropped from view in July. And it won’t return to view in the evening sky until late September or early October, depending on your latitude. Then Venus will begin a long run as the “evening star” — until it vanishes once again, in late May.

Tomorrow: Looking for powerful cosmic “death rays.”

Script by Damond Benningfield