Winter sure didn’t sneak up on us this year. Astronomically, winter officially begins on Sunday Dec. 21 at 7:04 am EST, which is nice, because the beginning of winter is the beginning of the end. From Sunday on, the days will get longer, and West Michigan usually begins to see a bit more clear sky.
When it does clear up, the winter sky is always a wonder.
Astronomers have mapped the sky onto coordinate systems to help locate things. The simplest useful coordinate system is the altitude and azimuth system. Everyone has their own altitude and azimuth coordinate system. The center of your coordinate system is the point directly over your head, called the zenith. The altitude of the zenith is 90 degrees.
The altitude of the horizon is 0 degrees. Anything between the horizon and the zenith has an altitude between 0 and 90 degrees. Halfway is 45 degrees.
Azimuth is the compass direction you need to face in order to see something in the sky most conveniently. Around the horizon, north is 0 degrees, east is 90 degrees, south is 180 degrees and west is 270 degrees.
Your sky is divided into an east half and a west half by an imaginary line that runs from the north point on the horizon, overhead through your zenith, to the south point on the horizon. This line is called the meridian. The meridian is useful because as celestial objects rise and set, they reach their greatest altitude, and thus are easiest to see, when they cross the meridian.
When the clouds take a break from casting gloom over West Michigan, look along the meridian to the south a couple of hours after sunset for some of the brightest, most conspicuous stars and constellations.
Canis Major and the brightest star in the sky Sirius are low in the southeast, Orion, with bright blue Rigel and glowing red Betelgeuse, is at an altitude of about 45 degrees on the meridian, and Taurus the Bull, with the star Aldeberan marking his glowing red eye, are higher and to the west. Also look for the Pleiades, the tight cluster of stars, sometimes called the seven sisters, riding on Taurus’ back.
Closer to home, look for Jupiter and Venus low in the west and southwest. Jupiter at an azimuth of about 200 degrees and an altitude of about 30 degrees; venus at an azimuth of about 250 degrees and at an altitude of about 20 degrees. Both planets are very bright.
Also, early in January, you may catch a glimpse of fleet-footed Mercury. The closest planet to the sun is best situated for viewing on Jan. 4 2009 when it is at it greatest eastern elongation. Look for Mercury then at an altitude of about 10 degrees above the west-southwest horizon as soon after sunset as the stars begin to shine.
In the morning, you may see Saturn drifting between Leo and Virgo across the meridian at an altitude of about 50 degrees. But don’t look for Saturn’s rings these days (you would need a telescope anyways); Saturn’s thin ring system is oriented just about edge-on toward earth. Saturn’s rings won’t be visible again for about a year.
Happy holidays, and enjoy the snow. It won’t be long until we see more of the sun and sky.
This column originally appeared in the Grand Haven Tribune on 19 December 2008.
