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September 22: The autumnal equinox
The bright Moon stands prominently in Aquarius the Water-bearer this evening, quickly waxing toward Full. Swing your scope up toward Earth’s lone satellite tonight and focus in on a point just east of the terminator dividing night and day, roughly midway along the western limb. There, a strange light-colored feature, Reiner Gamma, just barely catches the eye. Astronomers aren’t sure what caused this swirly, splotchy mark, although they know it is a magnetic feature and not a topological one. It will stand out even more tomorrow night, on the 24th, if you’re having trouble seeing the light-dark contrast here tonight.
Just east of Reiner Gamma is the crater Reiner, which hosts a noticeable central peak. And just west of Reiner Gamma is Galilaei and its smaller companion, Galilaei A, to the north. Can you see the rille snaking between Galilaei and Galilaei A? Northeast of these two craters lie the Marius Hills, a gaggle of volcanic domes once considered as an Apollo landing site, though it was never actually visited by astronauts. Just west of these domes is the wriggling shape of another rille, called Rima Galilaei.
Sunrise: 6:49 A.M.
Sunset: 6:55 P.M.
Moonrise: 5:32 P.M.
Moonset: 3:27 A.M.
Moon Phase: Waxing gibbous (93%)
*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.
