Mercury ends its prograde motion and prepares to enter retrograde in Libra the Balance — spot it after sunset if you’re quick.
Mercury hangs just 1° above the western horizon half an hour after sunset on October 24. Look for the stars of Scorpius in the southwest to help guide you toward the planet’s position. Credit: Stellarium
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October 23: Nab Neptune near the Moon
Mercury reaches a stationary point in Libra at 8 A.M. EDT. The tiny planet is only briefly visible after sunset, but if you’ve got a clear horizon, give it a try. Look west roughly 20 to 30 minutes after sunset, and scan for a magnitude 0.5 point of light just above the horizon. Mercury is 2.5° high in the southwest 20 minutes after sunset, and 1° high in the west 10 minutes later. You may want to try sweeping the area slowly with binoculars, but make sure the Sun has set completely below the horizon before pulling out any optical aid. Mercury’s disk stretches 9” across and the planet is 28% lit if you can catch it through a telescope.
Today’s standstill marks an end to Mercury’s prograde, or eastward, movement. After this, it will begin tracking westward, or retrograde, heading back past Alpha (α) Librae in just a few days and crossing into Virgo in early November, joining Venus.
Sunrise: 7:21 A.M.
Sunset: 6:07 P.M.
Moonrise: 5:05 P.M.
Moonset: 5:35 A.M.
Moon Phase: Waxing gibbous (98%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 10 P.M. local time from the same location.
Alison Klesman is senior editor of Astronomy magazine. She holds a Ph.D. in astronomy and has studied a variety of topics, from minor planets to supermassive black holes.