This is Dudley Observatory’s Skywatch Line for Friday, September 30, through Sunday, October 2, written by Sam Salem.
The New Moon occurs at 8:11pm on Friday; Sun rises 6:52am and sets at 6:38pm. On Sunday, look for the 3% illuminated Waxing Crescent Moon in the western sky, shortly after sunset. Each successive evening watch the Waxing Moon farther east of the setting Sun and staying out longer after sunset. Watch for the Crescent Moon and Venus on Sunday in the western evening dusk around 20 minutes after sunset. The slender Crescent Moon and Venus will follow the Sun below the horizon before nightfall. Moon sets at 7:40pm and Venus sets at 7:46pm, on Sunday.
Venus is climbing a bit higher each week. The –3.9 magnitude “evening star” can be spotted very low in the west-southwest shortly after sunset. Saturn shines at magnitude +0.5 in the southwest. Mars is drifting away from Saturn and Antares. The red planet is now magnitude 0.0 and residing in Sagittarius, just above the spout of the Sagittarius Teapot. Mercury rises due east nearly 90 minutes before the Sun.
The New Moon weekend is always an opportunity to do some deep-sky observing. The Double Cluster in Perseus ranks as one of the favorite deep-sky objects among stargazers. In spite of their prominence, the side-by-side clusters didn’t make into Charles Messier’s well-known list. The eastern and western clumps of stars are catalogued, respectively, as NGC884 and NGC869. Look for Constellation Cassiopeia in the northwest. Just above Cassiopeia you’ll see a faint fuzzy patch. This is the Double Cluster. Binoculars provide a good view of the Double Cluster and its surroundings. Note the sprinkle of orange stars scattered among the ice-blue cluster gems. The Double Cluster was charted by skywatchers as early as 150 B.C. Hipparchus saw it, and Ptolemy named it as one of seven “nebulosities” in the Almagest.
Follow Sirius into daylight this weekend. Sirius rises at 1:57am, reaching transit altitude at 6:55am 30 degrees south. Deneb takes over from Vega as the star at the zenith after dark, while Capricornus takes over from Sagittarius as the zodiacal constellation standing due south. The pathway of the Sun and Moon was called the Zodiac, or Pathway of Animals, in recognition of the constellations seen beyond it.
Zodiacal light, or false dawn, can be viewed from the east before morning twilight for the next few days. The zodiacal light is best seen when there is no moonlight or light pollution. Zodiacal light is a faint diffuse white glow seen in the night sky that appears to extend up from the vicinity of the Sun along the ecliptic or zodiac. It is caused by sunlight scattered by space dust. This light would cover the entire sky and is responsible in large part for the total skylight on a moonless night. The light looks like a hazy pyramid. Maybe you’ve seen the zodiacal light in the sky already and haven’t realized it.