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Wyoming Skies for March


February 27, 2009 — A monthly look at the night skies of Wyoming, written by Ron Canterna, professor in the University of Wyoming Department of Physics and Astronomy.

A spectacular view of the plane of our Milky Way presents itself at about 9 p.m. This hazy band of unresolved stars stretches from the southern horizon through the constellations Gemini and Orion, which are about 45 degrees above the western horizon, and then passes down to the northern cardinal point on the horizon.

Starting from the southern horizon, the Milky Way passes through the constellation Canis Major and the bright star of Sirius, Canis Minor, the twins of Gemini, Auriga, the yellowish-star Capella (the She-Goat), Perseus and finally resting on the northern horizon at Cassiopeia (W-shaped).

Look for the Orion nebula, the Pleiades and the Hyades cluster of stars in the constellation Taurus the Bull (V-shaped) and stars of various colors, like the reddish Betelgeuse in Orion, orange-colored Aldebaran (eye of the Bull), bright-white Sirius low on the southeast horizon and the yellow star Capella.

Take a small pair of binoculars, gaze at the hazy Milky Way and you will see more stars and star clusters than you ever thought existed because you are looking through the plane of our galaxy.

This month, Venus changes rapidly and becomes the morning star at the end of the month. Saturn will be in Leo and you can follow it throughout the night. The first day of spring arrives March 20.

March 2009 Interest: What is a star cluster?

When you look at the night sky, you generally see stars randomly distributed all over the sky. Although some stars appear to be grouped together and make up a constellation, these stars are not physically associated with each other. They just accidentally happen to be in the same direction in the sky and form some type of "connect-the-dot" figure," which we call constellations.

Sometimes, you may see a small grouping of stars that are not accidental features, such as the Pleiades (the Seven Sisters) or the V-shaped Taurus the Bull, whose grouping is best seen through binoculars. If you look closely at the Pleiades or Taurus, or if you look into the Milky Way with binoculars or a telescope, you may see many more groupings of stars, called star clusters.

These star clusters appear to form a spherical assembly of stars because they are physically associated with each other by their gravitational forces. In fact, most astronomers believe that the individual stars in these star clusters formed at approximately the same time and from the same gas and dust, or "star stuff."

They also orbit each other like bees around a hive, while the group as a whole orbits the center of the Milky Way. It takes about 200-300 million years for star clusters to complete one orbit around the center of the Milky Way. Eventually, after many hundreds or thousands of millions of years, these cluster members will disperse throughout the entire plane of the galaxy and the cluster will no longer exist.

For more information, visit the Wyoming Skies home page (http://wyoskies.uwyo.edu) or send an e-mail to canterna@uwyo.edu.

Posted on Friday, February 27, 2009

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