Seventeen Day Old Moon‡

Tonight's Waning Gibbous Moon will rise during the very late afternoon and sets in the mid-morning sky. It transits several hours after midnight, and is well positioned for observing tonight.

A few days before and after the Full Moon, some features become particularly bright. Recent impacts are especially notable for this. Because the Moon is so bright overall and with small shadows about the time of Full Moon, these make some of the best features to observe.

 

Key Features to Observe Tonight

Tonight the large dark sea to the north of the equator, Mare Crisium, is half in shadow. South of it, Mare Tranquillitatis (the Sea of Tranquility) is also being thrust into the terminator tonight. To the north from Mare Crisium just beyond its edge, near the terminator, three craters from last night appear for the last time this lunation: Cleomedes, Geminus and the worn walled plain Messala. Well beyond them, by the lunar arctic circle one sees the prominent dark Endymion, again, for the last time tonight.

Well south of Mare Crisium, on Mare Fecunditatis, Langrenus lies very close to the terminator. It shows strong relief in this light, a contrast to its bright ring appearance during the Full Moon.

South of Langrenus lies Snellius whose degraded contours reveal its considerable age, in contrast to the sharp edged Langrenus. To its south lies Stevinus with a very large central peak, also close to the terminator and which shows well. Stevinus A and Furnerius A (to the southeast) are a pair of bright spots seen here. Stevinus A, though small (under 10 miles in diameter), has a ray system which extends over 1000 km (600 miles).

 

Features to Revisit

Tycho: A young crater with a bright ray system unmatched in beauty.

Aristarchus: An outstanding ring mountain in the western hemisphere.

Copernicus: The most conspicuous feature after Tycho. It serves as a good reference point for locating other objects. A trio of ray craters lies in the area about Copernicus. To the north is Pytheas, one of the most highly reflective areas of the Moon. West of it is Kepler, and to its northwest is Aristarchus. Together, they make an easily recognized trio, outlined by their rays.

Reiner and Reiner Gamma: To the west of Kepler. Reiner Gamma, to the west of Reiner itself, is a unique bright feature which shows no relief whatsoever. It is more like a bright deposit of some type on the surface, than an impact.

Euclides: Has a wide cone of bright ejecta lying along a line from craters Kepler to Tycho.

Anaxagoras: Another relatively recent impact with an impressive ray system.

Posidonius: Another well seen crater, though without any rays.

Linné: Only about one mile wide, but exceedingly bright.

Manilius and Menelaus: South of Linné; both are bright craters.

Dionysius: A bright, recent crater at the western edge of the Mare Tranquillitatis.

Proclus: Located between Mare Tranquillitatis and Mare Crisium. Proclus has a ray system that is uneven. Its strong ray to the west is particularly arresting.

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‡with permission from Lunar Discoverer User's Manual by Robert Duvall, 2013