Day 20

The illuminated portion of the Moon has been waning (growing smaller) for several days now. During lunar sunset, Maurolycus, a large crater found in the rugged southern highlands, has an almost abstract appearance when seen in a telescope at low power. I'm struck by the central peak's shadow, which looks like a clock hand that nearly touches the outer edge of this 70-mile-wide depression. The crater walls, which in places soar 15,000 feet above the floor, are outlined in black.

Day 22

Many of the features seen in dramatic relief at first quarter are again visible along the terminator, except that the direction of sunlight has flipped. Northeast of Mare Nubium, the crater Ptolemaeus exhibits a hexagonal shape 95 miles across. Its stark walls are outlined in white, with shadows filling in the crater Herschel to its north. Here's a good place to crank up the power on your telescope and search the floor of Ptolemaeus for small craterlets. Attached at its southern lip is the crater Alphonsus, which displays a 3,800-foot-high central peak and walls that rise to twice that height. South of Alphonsus is another bold crater, Arzachel, with even higher ramparts. The interplay of light and dark creates a fascinating display — the central peak's shadow extends for half the crater's 60-mile diameter. In between Alphonsus and Arzachel, and less than half as big, look for Alpetragius. If you catch the sunlight just right, you'll see a half-dark interior sporting a white-tipped peak.

Day 23 By now the Moon doesn't rise until after midnight — so to do some lunar gazing you'll either have to stay up late or get up early. But it's worth it: if you're like me, you'll never get tired of seeing Rupes Recta, the Straight Wall. Tonight look for the thin white line of sunlight reflecting off its slope. The Moon offers stunning views like these every night as the terminator sweeps across the lunar landscape twice every month. I could only touch on some of my favorites here; you'll find others labeled on the map above. One thing's for sure: the Moon will seem different every time you look.