This article was contributed by community member David Baumgartner as part of a local series on astronomy.
Cassiopeia is one of the groups of stars known to many people. It comes in fourth in popularity after the Big Dipper, Orion, and the Pleiades.
The reason is its easily recognizable shape: like the letter W. People have been known to argue about whether it is a W or an M! Of course it depends on which way you are facing, and which position it is in as it revolves around the Pole Star. To the Greeks it was neither one, but a chair. Cassiopeia was one of the bad characters. As punishment she was tied to her throne, which was set close to the Pole of the sky. So it whirls around the Pole, and Cassiopeia has to spend half of every day upside down.
Cassiopeia and Ursa Major are the two brightest of the “circumpolar” constellations, and they whirl around opposite to each other. At times when Ursa Major is on the low side, next to the horizon, trees or low lying haze may prevent you from using its two pointer stars to find the Pole Star. So you can use Cassiopeia instead. Not as good as Ursa Major, but it will get you close. There aren’t many bright stars around that area with Polaris so it should be easy to find.
If you look at Cassiopeia when in its W shape, you will see five main stars. Counting from left to right, use the number three and four stars to draw an imaginary line to help locate Polaris. And just to make it a little harder, when it is in the M shape, I guess you could use stars number two and three to find your Pole Star.
Let’s see what December skies bring us for viewing. I always enjoy the rain, so I have a tendency to wish for rain in the daytime and clear skies at night. Although I don’t seem to have any control over this timing.
I whish you all Season Greetings, and for the best evening skies ever.
December Sky Watch
Dec 18: Last Quarter Moon occurs at 8:57 p.m.
Dec 18: Moon is at perigee (230,072 miles from Earth) 12:25 p.m.
Dec 21: Winter Solstice for the Northern Hemisphere begins at 8:19 p.m. Shortest day of the year.
Dec 22: Moon passes 4° north of Mars, 6 p.m.
Dec 22: Ursid meteor shower peaks
Dec 25: New Moon occurs at 9:13 p.m.
Dec 27: Moon passes 1.2° south of Saturn
Dec 27: Moon passes 0.6° south of Pluto at 7 a.m.
Dec 28: Moon passes 1.0° south of Venus at 6 p.m.
Dec 31: Moon passes 4° south of Neptune 1 p.m.