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May 22: Busy moons around Jupiter
The Moon passes 0.08° south of Regulus at 3 A.M. EDT. A few hours later, First Quarter Moon occurs at 7:11 A.M. EDT.
First Quarter Moon offers some great targets for lunar observers. Plus, the great thing about the Moon is that it’s easy to find and focus on, so it doesn’t matter whether you’re a new or experienced skywatcher. Tonight, the Moon is still high in the southwest an hour after sunset, with the entire eastern half of the nearside now illuminated.
You don’t need to wait for full dark to zoom in on the Moon with a telescope. Concentrate your view along the terminator, the dark line dividing lunar night and day. In the north, just above the broad, dark oval of Mare Serenitatis, you’ll see two circular craters in a north-south line: these are Aristoteles in the north, and Eudoxus just south of it. Now scan just west of Aristoteles. Not far away is a large, dark slash in the brighter, rugged terrain. This is Vallis Alpes, a valley cutting through the Montes Alpes lunar mountain range on the northeastern rim of Mare Imbrium. This gash in the mountains is roughly 103 miles (166 kilometers) long and some 10 miles (16 km) wide at its widest. Note that one side of the valley — the southern side — appears much straighter than the slightly rounded northern edge. There is a thin, hard-to-spot rille, or groove, running lengthwise through the center of the valley. It can be a challenging detail to view, but crank up the magnification and see if you can spot it. If not, come back in a day or two, when there is more illumination in this region, and try then.
Sunrise: 5:38 A.M.
Sunset: 8:16 P.M.
Moonrise: 12:55 P.M.
Moonset: 1:45 A.M.
Moon Phase: Waxing gibbous (57%)
*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.
