The Constellation Bo÷tes


  1. We will now follow the handle of the Dipper and arc to Arcturus, a star in the constellation Bo÷tes (pronounced boo-OH-teez). {Trace out Bo÷tes}. Bo÷tes is a herdsman and the Guardian of the Bear -- Ursa Major. It is usually pictured as a guy just standing there, often with a staff but there are no stars to show the staff. Use your imagination. Notice how we could continue the line from the dipper's handle down to Spica.

  2. Next to Bo÷tes is Corona Borealis, the northern crown. {Trace out Corona Borealis}. The brightest star is a (alpha) Corona Borealis. This star is part of the same moving star group as the stars of the Big Dipper! It is called the "Ursa Major Moving Group" and is the closest star cluster to us at 75 light-years away. This group includes all the stars of the dipper except the tip of the cup and the tip of the handle. Along with a Corona Borealis, the group also has ten additional, fainter stars mostly in Ursa Major.

  3. Note Bo÷tes is a kite-shaped constellation. It used to be a shorter kite -- in ancient Greek & Roman times (2,000 years ago) Arcturus was half the distance closer to the two center stars (epsilon & rho Bo÷tes). It is moving across the sky faster than any other bright star (except Alpha Centauri which is ten times closer) -- it couldn't be seen 500,000 years ago and 500,000 years from now it won't be visible any more. Why is Arcturus moving so fast?

    The stars of our galaxy are formed into a rotating disk and are all moving together around the disk. Some stars -- called "halo" stars -- form a dome over the disk, Arcturus is one of those stars, orbiting above and below the galactic center. It is cutting through the disk now, actually a little bit back against the general flow. Someone on a planet orbiting Arcturus would see the entire night sky changing constantly.

  4. To the right of Bootes, just below the handle of the dipper, you can see two stars. The brighter one is called "Cor Carolis" -- it means the heart of Charles (King Charles II). These two stars form the constellation Canes Venatici. If you look carefully you can pick out two faint, scraggly diagonal lines of stars, one of which includes the two stars I just pointed out and the other is just a little above it. These two lines are two dogs on a leash held by Bootes -- come on, use your imagination -- and are helping him in his duties as herdsman and guardian of the bear.

  5. Now, if you look with the binoculars about halfway between Arcturus and Cor Carolis you will find a faint fuzzy spot -- this is M3, from Messier's catalog, and once we get a telescope on it you will discover it's one of the treasures of the deep sky. This is not just any star cluster -- notice how it looks like a little globe of stars? For that reason this kind of cluster is called a "globular cluster".

    Globular clusters are rare - only about 150 are known, and they are completely different from open clusters like M35 that we saw in Gemini.

    M35 is estimated to be about 100 million years old, while M3 is estimated at about 10 BILLION years old, making it so old that it formed before the disk of the Milky Way galaxy formed! While M35 has several hundred stars in total, M3 has several hundred thousand stars. M35 is about 3000 light-years away and about 30 light-years across, M3 is 40,000 light-years away and 220 light-years across.

    These numbers are typical, so globular clusters are much, much bigger than open clusters, and they are much, much older - some are nearly as old as the universe!


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All content material was graciously provided and used by the permission of  Randy Culp