This is the Dudley Observatory Skywatch Line for Wednesday, October 23rd, and Thursday, October 24th, written by Louis Suarato.
The 24% illuminated, waning crescent Moon sets at 4:06 p.m. Wednesday, and leaves the sky dark for observing. Astronomical twilight begins at 7:35 p.m., when the Sun is 18 degrees below the horizon, and all visible celestial bodies can be seen. Try to catch Mercury and Venus before they set at 6:30 p.m. in the west-southwest. At 7 p.m., Jupiter will be 14 degrees above the southern horizon, and Saturn shines 22 degrees above the south-southwestern horizon. The 20% illuminated, crescent Moon rises at 2:50 a.m., below Leo’s brightest star, Regulus. Mars rises at 5:47 a.m., completing the procession of easily visible planets.
Claudius Ptolomy was an Egyptian astronomer born in 100 AD. Ptolomy wrote The Almagest, which is contains a star catalogue and a list of 48 constellations, which was the prelude to today’s 88 modern constellations. Groups of stars within constellations that also form shapes to assist in celestial navigation are asterisms. Some of the brighter and larger asterisms include The Gtreat Diamond. This asterism consists of the stars Arcturus, Spica, Denebola, and Cor Caroli. Another bright asterism is the Great Square of Pegasus. This large asterism is comprised of the stars Markab, Scheat, Algenib, and Alpheratz. One of the most popular asterism is the Big Dipper, made up of the brightest stars within the constellation Ursa Major. The Northern Cross is an asterism at the center of the constellation Cygnus, the Swan. The four stars at the center of Hercules form the asterism known as the Keystone. The curved group of stars that form the lion’s mane in Leo is also known as The Sickle. Within Sagittarius is the Teapot asterism, with the Milky Way as its steam. Some telescopic asterisms are The Coathanger in Vulpecula, the Christmas Tree Cluster in Monoceros, and the Toadstool asterism, or French 1, in Delphinius, discovered and named for Sue French.