Twenty-Five Day Old Moon‡

The Moon appears as a crescent in the eastern sky today. Rising well after midnight, and transiting around 8 or 9 am, the best time to observe the Moon will be during the last hours of darkness, before the dawn.

 

Key Features to Observe Tonight

We begin tonight's tour observing at the polar region near the westernmost end of Mare Frigoris, which is barely visible tonight. Here lies the crater John Herschel, an old, well-worn crater, but well-defined under this light. We continue tonight's tour with Harpalus, lying to its south, noted for having three central peaks. Next, we come to Mairan, a recent crater impact with a sharp rim wall, a notable feature for study.

Looking to the southeast, across the Jura Mountains (part of the Iridium rim) lies the Sinus Iridium, about a third of the way from the northern cusp to the equator. Tonight it is bisected by the terminator, and resembles a large bite taken from the Moon's edge.

South of the Jura Mountains, on the Procellarum plain, is where the Soviet probe Luna 17 soft-landed. It included the rover Lunokhod 1, the first vehicle to travel on lunar soil (1970). Unfortunately, all human artifacts left on the Moon are much too small to be seen with even the largest telescopes in the world.

Continuing south, our eye is inexorably drawn to the extraordinarily bright crater Aristarchus, situated about the same distance again that Mairan lies from Harpalus, at about the same distance from the terminator.

Just north of the equator and nearer the terminator, the striking crater Kepler is better able to capture our attention tonight, with bright Copernicus to its east in the darkness now. Kepler's ray system, now becoming dim under low illumination, can still be traced across much of the Oceanus Procellarum where it impacted.

Looking west to the limb, southwest of Kepler, beyond Oceanus Procellarum, lies the crater Grimaldi, which is a dark and distinctive oval on the lunar surface. It remains a great study nearly to the New Moon. Southeast of Grimaldi is the walled plain Gassendi, which impacted the northern rim of Mare Humorum (seen in its entirety for the last time tonight).

The crater Hainzel, a complex feature of three intermingled craters makes a great study tonight, when it makes its last appearance this lunation. Finally, we come to Schiller, the most pronounced illustration of an elongated crater, with its long diameter over twice that of the short dimension.

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