Saturday May 21
Mercury reaches inferior conjunction at 3:00 p.m. EDT. The smallest planet in the solar system will reappear in the morning sky by next month.
Instead, let’s focus on a few other planets to the east early this morning. Two hours before sunrise, Jupiter, Mars, and Neptune all share the Pisces region directly below (to the southeast) the Circlet asterism. The Circlet consists of seven stars: Gamma (γ), 7, Theta (θ), Iota (ι), 19, Lambda (λ) and Kappa (κ) Piscium. This approximate circle of stars lies about 12° south of a line drawn between Algenib and Markab, which marks one side of the Grand Square of Pegasus. Gamma Psc is the brightest of the bunch – thought luminosity is relative, as it shines at magnitude 3.7.
While your eyes are on the Circlet, take a look at 19 Psc, also cataloged as TX Psc. It is a variable star whose unmistakable dark red color comes from the abundant carbon in its atmosphere. TX Psc fluctuates between magnitude 4.9 and 5.5 over approximately 220 days.
Now look down at the horizon from TX, and you’ll fall directly on Jupiter, shining at magnitude -2.2. About 5° to the upper right (west) is Mars, a reddish magnitude of 0.7. Neptune, whose magnitude 7.8 glow will require binoculars to spot, lies an additional 2° west of Mars.
Magnitude 0.7 Saturn lies far to the west, lingering in Capricorn near the 1st magnitude star Deneb Algedi. And in an hour, Venus will climb above the horizon, the brightest of our morning planets at magnitude -4.2.
Sunrise: 5:40 am
Sunset: 8:14 p.m.
Moon setting: 11:09
Moon phase: Waning gibbous (62%)
Sunday May 22
The Moon passes 4° south of Saturn at 1:00 a.m. EDT. One hour before sunrise, while the sky is still dark, our satellite is just over 5° directly below (southeast) the ringed planet in the southeastern sky. Although much of the moonlight washes away nearby Saturn, it’s still worth trying to glimpse the planet’s magnificent ring system through a telescope.
Then turn your gaze to the Moon. The large circular Mare Imbrium stands out in the lunar northwest, its southeastern edge marked by the rugged Apennine Mountains, named for the terrestrial mountain range in Italy. Just to the south is the bright Copernicus Crater, which stretches for about 93 kilometers. This lunar pockmark is extremely young, probably less than a billion years old, with several bright rays of ejecta – material thrown and pushed away by the impact – around it.
The last quarter moon occurs shortly after noon at 2:43 p.m. EDT.
Sunset: 8:15 p.m.
Moon setting: 12:21 p.m.
Moon phase: Waning gibbous (51%)