This is the Skywatch Line for Monday and Tuesday, December second and third, written by Joe Slomka.
The Sun sets at 4:22 PM; night falls at 6:03. Dawn begins at 5:27 AM and ends with the Sun rising at 7:08.
Monday’s Moon, in Capricornus, rose after Noon, is highest at 5:08 PM sets at 10:13 PM and is 39% illuminated. Tuesday’s Moon, in Aquarius, appears 47% lit, is highest at 5:53 PM and sets at 11:14 PM. The Moon turns officially “First Quarter” Wednesday at 1:58 AM.
Jupiter, Venus and Saturn, all in Sagittarius, continue to hug the western horizon. At about 40 minutes after sunset, Jupiter glows with minus 1st magnitude, but sits only 6° above the horizon; it sets at 5:35 PM. Venus, to Jupiter’s upper left, blazes with minus 4th magnitude appears about 49% lit and sets at 6:05 PM. Saturn, 11° to Venus’ upper left, shines with zero magnitude and is high enough for telescopic glimpses of its famous ring system, before it sets at 6:58 PM.
Night reveals Neptune and Uranus. Neptune, still in Aquarius, glows with 8th magnitude, is a tiny 2 arc-seconds in size, appears highest at 6:18 PM and sets at 11:53 PM. The nearby Moon may hinder observation with its brilliance. Uranus, in Aries, is brighter with 5th magnitude and appears a bit larger than Neptune. Its distance from the Moon may assist in observation. Uranus is highest at 9:13 PM and sets at 4:01 AM. Finder charts for these planets are available from astronomy magazines and websites.
Civil Dawn sees Mars, in Libra, about 20° high in the eastern sky. It displays a first magnitude red dot, about 4 arc-seconds in size. Mars rises at 4:29 AM. Mercury saw its highest point last week and is starting a rapid decline. Rising also in Libra at 5:26 AM, it shines with minus zero magnitude but appears larger than Mars and is 61% lit. The intrepid early morning observer should work quickly due to the brightening pre-sunrise sky.
French astronomer Pierre Mechain discovered M75 in 1780, in the constellation Sagittarius. He told his good friend comet hunter Charles Messier, who listed this object as number seventy-five in his list of comet lookalikes. In 1784, British astronomer William Herschel estimated the distance to this “nebula without stars” as six thousand light-years. We now know that M75 is a globular star cluster. Globular clusters are usually found around galaxy halos and Globulars bulges. Globulars may contain up to a million stars and are quite large, in a sphere about 100 light-years across. These stars are quite old. Modern estimates place M75 at about fifty-nine thousand light-years away. Astronomers also describe it as one of globulars compact globulars in the sky. Only the largest telescopes can resolve the cluster into individual stars.