This unique pair of craters was created by just one impactor that skipped along the lunar surface, leaving a cometlike tail of ejecta.
The double crater Messier in Mare Fecunditatis’ western region sports a long, tail-like ray of ejecta. Credit: Consolidated Lunar Atlas/UA/LPL
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October 14: Io covers Callisto
An hour after sunset this evening, you’ll find the waxing crescent Moon low in the southwest, hanging above the back of Scorpius and just off the spout of Sagittarius’ Teapot. Zoom in with a telescope on Mare Fecunditatis, the large dark splotch that lies just below the much rounder Mare Crisium. In Mare Fecunditatis’ western region, look for a pair of small craters with a signature white “tail” spreading westward — this is the doublet Messier, named for the famous French comet hunter Charles Messier, whose name persists on his Messier Catalog of deep-sky objects.
Of the two, Messier is the easternmost crater, while Messier A lies just west of it. The pair was created by the same event, as a comet nucleus or asteroid came in at a glancing angle, skipping off the surface like a rock skipping on water and coming down to create a second crater. Astronomers believe Messier was the initial impact, while the skip created Messier A, just 4 miles (6 kilometers) away.
Take some time to study this intriguing pair, including comparing and contrasting their shape and depth. They’re definitely fraternal twins, not identical ones!
Sunrise: 7:11 A.M.
Sunset: 6:20 P.M.
Moonrise: 12:25 P.M.
Moonset: 9:11 P.M.
Moon Phase: Waxing crescent (30%)
*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.