This Week's Sky at a Glance for December 17 – 25

This Week's Sky at a Glance
Some daily events in the changing sky for December 17 – 25
by Alan M. MacRobert
The Moon takes three nights to pass from one end of the constellation Taurus to the other. (These scenes are drawn for the middle of North America. European observers: move each Moon symbol a quarter of the way toward the one for the previous date. For clarity, the Moon is shown three times its actual apparent size.)
Sky & Telescope diagram
Friday, December 17
 
This evening look lower left of the Moon, by a little more than a fist-width at arm's length, for the delicate Pleiades star cluster. (The Moon is still outside the scene at right.) Below the Pleiades by a roughly similar distance is orange Aldebaran. Far off to their left shines brighter Capella.
 
Saturday, December 18
 
The Pleiades are only about 2° left or upper left of the gibbous Moon as seen from North America this evening, as shown at right. Use binoculars to penetrate the bright moonlight.
 
Sunday, December 19
 
This evening the Moon, one night before its total eclipse when full, shines in the east with Aldebaran to its right or lower right and brighter Capella more than twice as far to its left.
 
Monday, December 20
 
Total eclipse of the Moon late tonight, visible from all of North and Central America. The partial phase begins 1:33 a.m. Tuesday morning EST, total eclipse runs from 2:41 to 3:53 a.m. EST, partial eclipse ends at 5:01 a.m. EST. For our part of the world the Moon will be very high in the sky; in fact from the American Southwest and Southern California it will be near the zenith. The Moon will be centered between the bright constellations Orion, Auriga, Gemini, and Taurus. Read all about it:A Sky-High Lunar Eclipse. Includes a map of the eclipse's visibility worldwide.
 
Time-lapse of a lunar eclipse. Aligning his camera on the same star for nine exposures, Sky & Telescope contributing photographer Akira Fujii captured this record of the Moon’s progress dead center through the Earth’s shadow in July 2000. (This image is available as a print-quality JPEG (1.5 megabytes) for media use; see ourpress release.)
Sky & Telescope / Akira Fujii
 
 
And, of course, the Moon is full (exactly so right around mid-eclipse).
 
Tuesday, December 21
 
This is the longest night of the year in the Northern Hemisphere; winter begins at the solstice, 6:38 p.m. EST. Gather 'round the fire. In the Southern Hemisphere it's the shortest night of the year and the start of summer; dance in Midsummer's Night merriment.
 
Wednesday, December 22
 
In early evening at this time of year, Cassiopeia floats as high in the north as it ever appears. It's loaded with telescopic sights to seek out. Some lesser-known ones are featured in Sue French's Deep-Sky Wonders column in the DecemberSky & Telescope, page 66.
 
Thursday, December 23
 
Jupiter's largest and brightest moon, Ganymede, reappears out of eclipse from Jupiter's shadow around 8:08 p.m. EST. A small telescope will show it gradually swelling into view just east of the planet — right near Callisto and Io. Watch the pair become a triple!
 
For a listing of all such Jupiter-satellite events this month, see the DecemberSky & Telescope, page 64.
Friday, December 24
 
Christmas star: Brilliant Sirius, the brightest star in the night sky, rises around 7 or 8 p.m. (depending on where you live in your time zone). Orion's Belt points down nearly to Sirius's rising point, showing where to watch for its advent. When Sirius is low it often twinkles in vivid, flashing colors, an effect that binoculars reveal especially clearly.
 
Saturday, December 25
 
MerrySol Invictus! In the late Roman Empire, December 25th was the Birthday of the Unconquered Sun, marking the Sun's survival past its seasonal dark decline with the promise of a new spring and summer to come. Along with other solstice-period celebrations (including the birthday parties of numerous pagan deities), the date and the symbolism were taken over by Christianity and officially set to be Christmas in the 4th century. Carefully note the sunset point on your horizon from day to day. Can you see that it's already beginning to creep a little north?
 
 
Christmas is the time of year when iconic Orion finally clears the east-southeast horizon and sparkles in full view shortly after twilight ends (for skywatchers at mid-northern latitudes).
 
 
The eclipsing variable star Algol is at its minimum light, magnitude 3.4 instead of its usual 2.1, for a couple hours tonight centered on 1:08 a.m. Sunday morning Eastern Standard Time (10:08 p.m. Christmas evening Pacific Standard Time).