This is the Dudley Observatory Skywatch Line for Wednesday, September 4th, and Thursday, September 5th, written by Louis Suarato.
The 27% illuminated, waxing crescent Moon leads Jupiter and Saturn into the west-southwestern horizon, where it will set at 10:12 p.m. Wednesday. Jupiter sets at 11:30 p.m., followed by Saturn at 1:22 a..m. Thursday. The Moon reaches its First Quarter phase at 11:10 p.m., Thursday. Earlier in the night, look for Jupiter four degrees to the Moon’s left.
The First Quarter is one of the best times for viewing the Moon, when long shadows detail the lunar features along the terminator. The terminator is a line that separates the side of the Moon illuminated by the Sun from the side of the Moon in darkness. Some of the lunar features to view during this phase are six seas, or “maria”. From the northern section of the Moon, locate Mare Frigoris, also known as the Sea of Cold. Next is Mare Serentatis, or the Sea of Serenity. Further south is Mare Tranquilitatis, the famous Sea of Tranquility, which was the landing site of Apollo XI, which carried Neil Armstrong and Buzz Aldrin, the first astronauts to walk on the Moon. Below the Sea of Tranquility is Mare Nectaris, the Sea of Nector. To the right of the Sea of Tranquility is Mare Crisium, the Sea of Crisis, and below the The Sea of Crisis is Mare Foecunditatis, known as the Sea of Fertility.
Some of the more prominent craters to observe during the First Quarter are Aristoteles, which is located south of the Sea of Cold. Aristoteles is 55 miles wide and 12,000 feet deep. To the east, or right, of Aristoteles are Hercules and Atlas. Hercules is 45 miles wide and 12,500 feet deep, and Atlas is 54 miles wide and 10,000 feet deep. To the south of Hercules and Atlas, on the northeast edge of the Sea of Sereity, is the crater Posidonius. Posidonius is 60 miles wide and very shallow. It is likely this crater filled with lava after impact. Between the Sea of Tranquility and the Sea of Serenity is the crater Pliny. Pliny is 27 miles wide with a very bright, reflective floor 10,500 feet below the crater’s rim.