Contellation of the Month, March 2004

Canis Major

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Canis Major, the "Big Dog", is prominent in the South on March evenings. Its a very easy constellation to find, because it contains the brightest star in the entire night sky, Sirius. To find Canis Major, use the familiar hourglass shape of Orion the Hunter, which is in the South-Southwest. Look to the lower left of Orion, and dazzling Sirius will immediately catch your eye. The name Sirius comes from the Greek for "scorching". Also known as the "Dog Star", Sirius has a tiny companion that is all but impossible to see visually. Sirius B is magnitude 8.44, ten thousand times dimmer than Sirius A at magnitude -1.9. Click here to read a fascinating article about an ancient west African tribe that knew of Sirius B's existence before it was discovered by scientists!
In addition, Sirius is one of our closest neighbors, only about 9 light years away. It is the fifth closest star to our own Sun. The ancient Egyptians worshipped Sirius as the "Nile Star", because when Sirius appeared in the pre-dawn sky at the beginning of Summer, it heralded the rising of the waters of the Nile. They built temples oriented in a way that the light from Sirius would penetrate deep into their interiors. You may have also heard of the "Dog Days of Summer". This expression comes from the Dog Star, which in North America and Europe makes its appearance in the pre-dawn sky in late July and August, signalling the hottest days of the year. Other bright stars that make up Canis Major include Mirzam (Beta, b), which is called "The Announcer" because it rises prior to Sirius; Wezen (Delta, d); Adhara (Epsilon e), and Aludra (Eta h).

In this larger, more detailed view, (adapted from Norton's Sky Atlas 2000.0), we'll take a closer look at some of the interesting sights in Canis Major. Our tour goes in order of Right Ascension, which is right to left on this map. The symbols below show how an object is best viewed:

with your naked eye;

with binoculars, and

with a telescope.


NGC 2204. Since Canis Major is right on the edge of the Winter Milky Way, it contains a lot of open star clusters. These are groups of young stars that have formed together in the spiral arms of the galaxy. NGC 2204 is easy to find, only 1 1/2 degrees west of Beta Canis Majoris. Its a farily large cluster with a concentration of stars in the western half.

NGC 2207. This is actually a very close pair of interacting galaxies which shines at magnitude 10.7. Its hard to resolve both of them unless you have a very large aperture scope, but you should be able to see a bright core and some spiral structure with a 6 to 10 inch scope. Click here to see a gorgeous image of these galaxies taken by the Hubble Space Telescope.

Sirius. Take a look at the Dog Star with your scope, binoculars, or just the naked eye. Sirius is actually a blue-white star, but many people see red, green, blue, and yellow in this shimmering star. This is because of the earth's atmosphere, which makes the stars twinkle. Because Sirius is so bright, and for northern hemisphere observers it is close to the horizon, the twinkling is much more noticeable. If Sirius were straight overhead in the sky, its blue-white color would be much steadier.

NGC 2354. This is a large, bright, rich open cluster that lies only 1.3 degrees east of Delta Canis Majoris. It's a great cluster to explore with binoculars or any size telescope.

NGC 2362. A large, bright open cluster that contains about 60 stars, the brightest of which is Tau Canis Majoris at magnitude 4.39. Tau has been called the "Mexican Jumping Star". Try observing this cluster with a telescope, and wiggle the scope a bit as you observe. Tau may appear to move differently than the other stars in the field, because of its brightness. This is a trick our eyes play on us when we compare bright objects to dim ones. More on NGC 2362.

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