The week of May 26 – June 1 takes us from Day 29 to Day 6. This week we will highlight the moon crater Messier, visible on Friday and Saturday nights.
Messier: [SE/K14; L=48°E] One of my favorite objects on the Moon is a small pair of moon craters named Messier and Messier A. They are located on the western lava plains of the Sea of Fertility and can be easily seen through the smallest telescopes. The moon craters have a pair of splash rays that resemble the tails of a comet (an appropriate resemblance, considering who they are named after). These rays, which extend about 75 miles to the west, have a happy characteristic in that they are visible under lower angles of illumination. It is unusual to be able to see both a moon crater and the rays it produced at the same time. (Tycho [SW/P8] is the most conspicuous example of splash rays.)
The most commonly accepted explanation of the origin of this unusual feature is that a projectile came in at a low angle (1° to 5°) from the east, smashed into the Moon to excavate Messier, and then ricocheted. When it landed the second time Messier A was formed, along with its attendant “comet tails.” The projectile’s extremely low angle of approach explains the oblong shape of the craters. Notice that the Messier impact created a butterfly pattern, typical of very low-angle impacts, while the ejecta from Messier A formed the two comet tails.
OF ADDITIONAL INTEREST IN SPACE
On Sunday, Mars is 1.4° south of the Moon.
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It is highly recommended that you get a copy of Sky and Telescope’s Field Map of the Moon, the very finest Moon map available for use at the telescope. It is available for $10.95 at www.skyandtelescope.com and on Amazon. All features mentioned in this blog will be keyed to the grid on the Field Map and will look like this: Plato: [NW/D9]
Credits:
Courtesy of Gray Photography of Corpus Christi, Texas
Lunar photos: NASA / USGS / BMDO / LROC / ASU / DLR / LOLA / Moon Globe. Used by permission
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