Skywatch Line for Friday, December 19, through Sunday, December 21, written by Sam Salem
This is Dudley Observatory’s Skywatch Line for Friday, December 19, through Sunday, December 21, written by Sam Salem.
On Friday, Sun rises at 7:22am and sets at 4:23pm; Moon rises at 7:24am and sets at 3:42pm. New Moon occurs at 8:43pm, on Friday.
Winter begins on Sunday at the solstice, at 10:03am. This is when the Sun halts its southward journey in Earth’s sky and begins its six-month return northward.
Mercury, magnitude –0.5, is slowly getting lower, rising a bit after the first hint of dawn light. Look for it low in the east-southeast as dawn grows, about 50 or 60 minutes before sunrise.
Jupiter, magnitude –2.6 in eastern Gemini, rises in the east-northeast about an hour after full dark. It dominates the eastern sky as the evening proceeds, then the high southeast. Castor and Pollux shine nearby. Jupiter is highest in the south in the hours after midnight. Jupiter doesn’t move against the starry background as fast as the inner planets do. Currently it’s moving westward in a retrograde motion on its way to opposition on January 10th.
Saturn, magnitude +1.1 at the Aquarius-Pisces border, shines high in the south at nightfall below the Great Square of Pegasus. It gets lower in the southwest through the evening and sets around midnight.
Uranus, magnitude 5.6, sits in the constellation Taurus, 5° south of the Pleiades. It is well up by 7pm. In a telescope, at high power, it’s a tiny non-stellar dot, 3.8 arcseconds wide.
Neptune, magnitude 7.8, is a dim speck, in a telescope, just 2.3 arcseconds wide. It lies 4° northeast of Saturn. Use a finder chart to identify Uranus and Neptune among similar-looking faint stars.
This moonless weekend is the best time to view deep-sky objects. The spiral galaxy M33, also known as the Triangulum Galaxy, is highest in the sky around 8pm. It sits 80° high in the south at this time. The 6th-magnitude galaxy is located in western Triangulum. The nearest bright star is 2nd-magnitude Mirach in the constellation Andromeda. From this star, the galaxy lies just 7° to the southwest. The best way to find M33 is to search with binoculars or a wide-field scope, locating it first. Then, zoom in with higher magnifications to look for its brighter core and fainter spiral arms. M33 spans about 70’ by 45’ on the sky. It is a member of our Local Group of galaxies, along with the Andromeda Galaxy and numerous smaller members.
On Saturday, Algol, in constellation Perseus should be at its minimum brightness for a couple hours centered on 7:17pm.