The Sky Today on Thursday, July 23: Mercury’s retrograde path ends
The solar system’s smallest planet comes to a standstill this afternoon, ending its current retrograde path and beginning to move east.
Look east before sunrise on the 23rd to see if you can spot tiny Mercury, not far above the horizon some 40 minutes before dawn breaks. Your best bet may be to look for the planet using binoculars, but make sure to put them away at least several minutes before sunrise from your location. Credit: Stellarium
Looking for a sky event this week? Check out our full Sky This Week column.
July 22: Dione passes north of Saturn
The planet Mercury is stationary at 1 P.M. EDT. Located in the constellation Gemini, the tiny world is now rising before the Sun, visible for a short time in the east before sunrise. However, it’s quite faint — magnitude 2.2 — and is best seen with binoculars or a telescope, to the far lower left of Betelgeuse in Orion, which itself stands left of the three star asterism Orion’s Belt. High above, magnitude 1.3 Mars is brighter and easier to spot, to the left of Taurus’ brightest star, Aldebaran.
Mercury is just 2° above the horizon around 5:10 A.M. local daylight time, although it’s rising. However, the sky is also brightening, so the earlier you can catch it, the better. A clear, flat horizon with no trees or buildings is best. Try using some optical aid to spot it, once you know you’re in the right area (or simply use the go-to function on your scope if you have it). Through a telescope, Mercury is just 12% lit, which is why it’s so faint despite its diameter of 10”.
Now that Mercury has paused its motion in our sky, it will stop moving westward, or retrograde, and begin moving eastward, or prograde. In the coming weeks, it will head for the eastern border of Gemini and cross into Cancer around midday on August 8.
Sunrise: 5:51 A.M.
Sunset: 8:22 P.M.
Moonrise: 4:03 P.M.
Moonset: 12:38 A.M.
Moon Phase: Waxing gibbous (75%)
*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.
