The week of August 14-20 takes us from Day 28 to Day 4. This week we will highlight the moon crater Messier, viewable Sunday after midnight.

Charles MessierMessier: [SE/K14; L=48°E] One of my favorite objects on the Moon is a small pair of 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 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 crater and the rays it produced at the same time. (Tycho [SW/P8] is the most conspicuous example of splash rays.)


On Friday Mercury is 7° south of the Moon, and Mars is 2° south of the Moon, a double whammy!


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 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]

Courtesy of Gray Photography of Corpus Christi, Texas
Lunar photos: NASA / USGS / BMDO / LROC / ASU / DLR / LOLA / Moon Globe. Used by permission

Andrew Planck
Messier Moon Crater: Pair of Splash Rays that Resemble Tails of a Comet
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