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Northern Rockies Skies for December

November 24, 2010

A monthly look at the night skies of the northern Rocky Mountains, written by astronomers Ron Canterna, University of Wyoming; Jay Norris, Challis Idaho Observatory; and Daryl Macomb, Boise State University 

The Geminid meteor showers, peaking on Dec. 13-14, could provide midnight watchers with one of the most spectacular showers this season, with up to 100 streaking "stars" every hour. Look east right around 9 p.m. for the twins Castor and Pollux and then track those colorful meteors throughout the night.

For the rest of the month look directly overhead for the distinctive Cassiopeia. This "W"-shaped constellation, which never sets below the horizon at our latitudes, represents the Lady in the Chair or the Queen of Ethiopia.

East of Cassiopeia lies Perseus, the Champion, and its brightest star Algol. Further east a small grouping of stars called the Pleiades is observed in Taurus (the Bull). The "seven sisters" is a relatively young star cluster actually containing well over 1,000 stars. Look for Sirius, the brightest star in the sky, late in the eastern sky.

For you planet watchers, Jupiter is up most of the evening while Saturn rises at 3 a.m. and Venus is December's morning star. A big treat for everyone this month a total lunar eclipse will happen on the winter solstice, Dec. 21. Get those binoculars out and enjoy the celestial Northern Rockies Skies.

December Interest: The Milky Way Galaxy I
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The most prominent feature of the night sky -- the Milky Way -- was a basis of myths and legends for all civilizations of antiquity.

The English name echoes those sounding more prosaic to us -- such as the Latin, Via Lactea. This Milky Way Galaxy is home to our solar system and many others.

From Earth the Milky Way appears as a wide band of light wrapping 360 degrees around the sky. This apparently continuous structure is actually uncounted numbers of stars, each individually too dim to be differentiated by the unaided eye.

Dividing the band of starlight are occasional distinct dark lanes, especially toward the constellation of Cygnus. Enormous dust clouds extinguish light from more distant stars behind the clouds, just like the brightness of a distant traffic light is diminished by dust in the air.

The plane of the galaxy is inclined about 60 degrees to the celestial equator. From North America the direction to the galaxy's center in Sagittarius lies low near the southern horizon during evenings in summer months. The actual galactic center is not visible in optical wavelengths -- it too is blocked by dust -- but can be observed using radio and far infrared portions of the electromagnetic spectrum.

The nature of our galaxy has been known for less than a century. In the "Great Debate" of 1920 between Harlow Shapley and Heber Curtis, both were later proven correct on their main positions:  Work begun by Edwin Hubble and continued by astronomers to the present day has shown that the Milky Way is just one of an estimated 100 billion galaxies in the observable portion of the universe (Curtis), and that our own solar system's position lies far from the galaxy's center (Shapley).

To see this month's sky chart, click here.

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