Fall's cooler evenings arrive with a cluster of planets in the west at twilight. Venus, Mercury, and Saturn are joined by the moon early in the month. Mercury was a morning object in August but has edged into the evening sky for September.
Venus is a brilliant magnitude -4.0 and looks like a plane with its landing lights on except that it doesn’t move. By September 5, Venus is a degree and a half above the star Spica. To Venus's upper left is the Ringed Planet Saturn, and to Venus's lower right lies Mercury. Because Mercury is so low and in the fading light of sunset, it may take a while before you can spot it. On September 7, a line consisting of Saturn, Venus, Spica, and Mercury spans 40 degrees from the southwest to the west. In addition, a thin crescent moon can be found below this line. The recently set sun will make it difficult to catch all the objects, however.
On September 8, catch a pretty photo-op when the crescent moon lies two degrees to the left of Venus, with Spica almost four degrees to Venus’s lower right. The next night the moon is wide left of Saturn. Saturn and Venus have been closing in on each other and will get to within three and a half degrees on September 17. Saturn is in the constellation Libra above Venus, while Venus lies in the constellation Virgo. On the next night, September 18, the planets keep their distance but Venus crosses the border to join Saturn in Libra. Following this date the planets start to drift apart.