June 1 through 7 (Waning Gibbous to Last Quarter)
Mare Nubium, the Sea of Clouds, has an unusually dark floor.
Mare Frigoris, the Sea of Cold, is most unusual in appearance. Instead of the typical circular plain, Mare Frigoris stretches over 1,000 miles (1,609 kilometers) but is no more than 45 miles (72 km) wide at points.
Mare Humorum, the Sea of Moisture, is a nearly circular dark plain to the south of Oceanus Procellarum. Measuring 230 miles (370 km) in diameter, its surface appears quite smooth through binoculars.
Sinus Iridum, the Bay of Rainbows, is a favorite lunar feature. Originally, Sinus Iridum was a complete crater, but its southern wall was washed away when lava from Mare Imbrium crashed against it. Two promontories, named Heraclides and Laplace, mark the opening of the bay’s 160-mile-wide (258 km) mouth, while the Juras Mountains form its northern perimeter.
Mare Crisium, the Sea of Crises, is a large oval plain measuring 345 by 375 miles (555 by 600 km), with the long dimension running east to west. This is just the opposite of the visual impression we get from Earth because of the foreshortening of the lunar globe. Unlike the other, interconnecting maria, Mare Crisium stands alone.
Langrenus, found on the southeastern shore of Mare Fecunditatis, is an amazing crater to watch from Waxing Crescent to Full Moon. As the Sun rises higher in its sky, 80-mile-wide (130 km) Langrenus seems to almost catch fire as its floor is transformed from a dull gray to a brilliant whitish glow.
Clavius, the second-largest crater on the Moon’s earthbound side, is one of the easiest to recognize. Its huge 136-mile-diameter (220 km) walls are especially prominent the night after First Quarter phase.
Kepler, although only 19 miles (30 km) across, is one of the most prominent craters on the Moon. Situated on central Oceanus Procellarum, its bright ray pattern may remind you of a miniature Copernicus crater.
Longomontanus is seen to the northwest of Clavius and southwest of Tycho, while another obvious crater, Maginus, is found an equal distance east of Clavius and Tycho. Collectively, all four create a conspicuous diamond pattern of craters near the Moon’s South Pole. Longomontanus measures 88 miles (142 km) across, while Maginus spans 99 miles (159 km).
June 8 through 15 (Last Quarter through Waning Crescent)
June 16 through 22 (New Moon through Waxing Crescent)
June 23 through 30 (First Quarter through Waxing Gibbous)