The crescent Moon charges through a rapidly disappearing group of bright stars and planets early this evening. Most of the group will be gone from view by the end of the month.

As twilight begins to fade, the planet Mercury is close below the Moon. Brighter Jupiter is the same distance to the left or upper left of the Moon. Pollux and Castor, the twins of Gemini, are to the upper right of the Moon. And the brightest member of the group is farther to the upper left of the Moon: Venus, the brilliant “evening star.”

Except for Venus, all the members of the group are dropping toward the Sun as seen from Earth. For Pollux and Castor, it’s because all true stars rise and set four minutes earlier each day. So every star disappears in the evening twilight at the same time every year.

For Jupiter and Mercury, the descent is due in part to the same thing – the daily shift of the starry background. But it’s also influenced by the relative motions of Earth and the planets themselves. Mercury is beginning a rapid dive toward the Sun, and will cross between Earth and Sun in a few weeks. Jupiter, on the other hand, is headed toward a passage behind the Sun as seen from Earth.

But Venus is actually moving farther from the Sun. It won’t reach its peak separation for two months, so it’ll remain in good view in the western evening sky into October.

We’ll have more about the Moon and Venus tomorrow.

Script by Damond Benningfield