RISING MOON
I Look again
THAT YOU CAN EXPERIENCE the pleasure of the unexpected when you see it under a new light is an idea that applies nicely to lunar observing. Craters, scarps, and valleys take on a new face under a sunset illumination, compared with their traditional appearance when the Moon is waxing toward Full.
Later in the evening of the Oct. 14 (around 11 P.M.), a waning gibbous Luna is oddly unfamiliar. First to catch the eye along the terminator is the snaking Serpentine Ridge, its relationship to the entire Sea of Serenity now easy to see.
Jump halfway to the pole to the large and detailed crater Aristoteles. The low Sun angle transforms its apron of impact splatter into an expanse of roughness whose texture is as fine as the night and your telescope allow. The north-south shadow line down its middle sports a large scoop. Trace this light back to the small crater breaching the western flank that lets the Sun shine through.
Farther north and west, Protagoras lies sunken in the basin of Mare Frigoris, almost resembling the hole in a golf green. Typical craters in the region have raised rims and western-facing flanks brightly lit by the setting Sun. But here, the ancient lava flow came right up to the western lip of Protagoras. Under a waxing crescent’s familiar lighting conditions on the evenings of the 1st and 31st, you might never suspect the unusual is hiding in plain sight.
The shadows intensify on the 16th, with the Sun dropping down in the lunar sky. Nearby, the Alpine Valley (Vallis Alpes) cutting diagonally through rough terrain is a sight always worth the time. If the atmosphere is steady, pump up the power and look for the rille running down its middle. The valley rim will still be illuminated on the 17th for a post-midnight view.