The Stars of Andromeda Legend
High in the east, some heroic constellations make for a remarkable sight.
On cold December evenings, an armada of bright winter constellations fills the sky from the zenith to the eastern horizon. But before we get into them, let's finish with the stars of late autumn.
Most sky watchers know the Greek saga of Andromeda, her parents, the queen Cassiopeia and the king Cepheus, as well as Perseus, who on his winged horse Pegasus saves the king's daughter from the sea monster (whale). All six mythological figures have found their place among the constellations in the sky. A guide to these figures is the Fall Square, or Pegasus Square, deep to the west. If the west of the overview map is down, you can see it just above the horizon.
The easternmost star of the quadrilateral isAlpheratz. It belongs to Andromeda, which is why its official name is Alpha Andromedae. It is the beginning of the main line of Andromeda, which stretches eastward across the equally bright stars Beta to Gamma Andromedae. Alpha marks the head of the king's daughter, Beta the waist and Gamma, a beautiful double star, the foot. Andromeda is shown in profile, stretching her less-light leg away to the northwest. Directly in front of her knee is M 31, the great Andromeda galaxy. You can see them with the naked eye under a dark sky. At the latest in binoculars it appears as an elongated spot of light. The light from this galaxy travels 2.5 million years before it reaches Earth.
East of Andromeda stands Perseus stretching one arm towards Andromeda's other foot. In Perseus is the famous eclipsing star Algol, which dims significantly for a few hours every 2.87 days.
Northwest down on the overview map, find Cepheus and Cassiopeia halfway to the zenith. Cassiopeia is a bright zigzag line of five stars. It resembles the letter W or M. Between it and Perseus lies the glorious double cluster H and Chi Persei. Observe it with binoculars or a telescope at low magnification.
Now if you rotate the map until south is pointing down, you will see that one foot of Perseus is pointing towards the Pleiades. The Seven Stars are a harbinger of the bright winter constellations rising in the east.
Below the Pleiades, the orange Aldebaran (Alpha Tauri) glows with the faint stars of the great Hyades star cluster. Aldebaran, a 1st magnitude star, is the bright eye of the bull (Taurus). Beside the bull rises the sky hunter Orion.
Planets in December
Venus is very low in the southwest after sunset. It's rising higher and higher all winter long and will shine brightly next spring.
Saturn rises earlier and earlier throughout the month, rising just after 8pm towards the end of December. With a telescope you can see it getting a bit bigger and brighter over time. Regulus (Alpha Leonis)stays below him.
Jupiter, Mercury and Mars get pretty close at dawn in the beginning of the month. Jupiter and Mercury shine quite brightly deep in the southeast, while Mars is much fainter. From December 7th to 14th, all three fit within a five degree diameter circle, corresponding to the viewing window of average binoculars. From December 9 to 11, the circle shrinks to 1.5 degrees, and at dawn on December 10December even to 1.1 degrees. This morning you can view all three planets simultaneously through a telescope if the eyepiece provides only low magnification. A pair of binoculars is also suitable. In addition, the double star Beta Scorpii fits into the viewing window. Unfortunately, they are quite low, so that air turbulence and haze on the horizon are very annoying.
The waning Moon rises near Saturn on the evening of December 9th and approaches the planets at dawn on the 10th. A thin crescent Moon hangs to the right of Jupiter and fainter Mars at dawn on the 18th. Back in the evening sky after sunset on the 22nd stands a very slender Moon twelve degrees to the left of Venus, just above the horizon.
The Sun arrives at the winter solstice on December 22 at 1:22 a.m. This marks the beginning of winter in the northern hemisphere and summer in the southern hemisphere.
You can observe two streams of shooting stars in December: On December 14th the Geminids have their activity maximum and on December 22nd the Ursids. © astronomy today