Three Day Old Moon‡

As the Moon continues to move further away from the Sun, it sets later each night. The Moon is now above the horizon in darker skies and it is easier to see detail with the better contrast a dark sky creates. Tonight's crescent Moon should be easily seen during the early evening, in the west. It will set a few hours after the Sun.


Key Features to Observe Tonight

When libration of the Moon is favorable, the very dark Mare Humboltianum may be seen near the limb. Although much foreshortened in appearance, it remains an interesting study.

The next most prominent object in the northern hemisphere is Mare Crisium, all of which is visible tonight, and it appears with good relief. The mare's contrast with the surrounding highlands will continue to improve over the nights to come.

Between these two mare lies several interesting craters. Starting in the north, just west of Humboltianum, lies the Endymion crater, with a sharp rim. To the southwest of it, by a couple of times its diameter, is a distinctive pair of craters: Atlas and Hercules to its west. Both Atlas and Endymion are seen to have dark patches on their floors when viewed in larger telescopes. Some observers believe them to vary in size and albedo, depending on the lunar day, but it is hard to explain a process responsible for any such change.

Continuing south, the walled plain Messala, north of Crisium by about one diameter, is seen in its entirety tonight, but it has lost contrast since last night, as shadows shorten with the rising sun. Messala's smooth-flooded floor will darken over the next nights, giving it an appearance like a small maria. Due south is the prominent bright crater Geminus, followed by the smaller and darker Cleomedes. The small craters on the floor of Cleomedes are shadow-filled and well-defined. They will be almost impossible to see in a few more days when the overhead sunlight floods the crater floor. A larger telescope will show a cleft (the Cleomedes Rille) crossing its floor.

To the south of the Mare Crisium, below the equator, the eastern portion of the dark Mare Fecunditatis has come into daylight. On its east edge is the prominent crater Langrenus. To its south, about its diameter away, is the cratered ring of walled plain Vendelinus. Moving about the same distance south again, lies the ring mountain Petavius. Petavius with its neighbors makes an magnificent sight. Its walls are eroded, but it has a magnificent central mountain chain, with multiple central peaks. A cleft stretches from the northern wall to those peaks, where it changes direction and heads west. The cleft is clearly visible in a small telescope.

Finally, midway to the southern cusp is another walled plain, Furnerius, which in a little over a week will be totally outshone by its small sister, Furnerius A.


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