The week of May 20-26 takes us from Lunar Day 17 to Day 22. This week we will highlight the craters Cleomedes and Proclus, viewable after midnight on Monday.
Cleomedes: [NE/G15] Cleomedes is the first significant crater just north of Mare Crisium. It is a splendid crater, 80 miles in diameter, with terraced walls, rilles, and a small central mountain. There are also four craterlets and a Y-shaped rille on the northern half of the floor just east of the central mountain peak. Notice that the floor is unusually smooth. Because its southern rim touches one of the multi-rings encircling the Crisium basin, it is believed that lava rose up through Crisium fractures and smoothly covered the floor of Cleomedes. Under a low-angle Sun you might be able to detect that the rille cuts through a small dome on the northern section of the floor.
Proclus: [NE/H14] Proclus is a small crater located just west of Mare Crisium. In spite of its size it is one of the brightest spots on the Moon. When you view it around full Moon you will notice it also has a system of rays that delicately fan out in a telltale butterfly-wing pattern, which tells you a lot about the flight path of the incoming projectile. Proclus is one of the best examples of what happens during a low-angle impact. (See ejecta and butterfly patterns in the Glossary.)
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]
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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