A new month brings a new constellation into the astronomical spotlight. This month's feature: a constellation that is truly impossible to miss thanks to the fact that it contains the brightest star in the entire sky. The star: Sirius. The constellation: Canis Major, the big dog.
Of all stars/constellations, Sirius/Canis Major is one of the most storied. Although no one knows where the association with dogs began, it was firmly established by the advent of historic times in Egypt. Back in Ancient Egypt, people believed that the star lent its heat to the Sun when it disappeared into the solar glare during summer as the disappearance of Sirius coincided with the warmest days of the year. This is where we get our modern term “dog days of summer.” For the Egyptians, the reappearance of Sirius heralded the beginning of a new year, too as the annual Nile flood would soon follow. From Egypt, the dog mythology about Sirius spread to other ancient cultures. The name “Sirius” is derived from the Greek “sothis,” meaning “scorching.”
Going out in February just after nightfall, one cannot help but see an extremely bright blue star low in the Southern sky. This is Sirius, the eye of the dog. With a little imagination, one can see very basic profile outline of a dog by looking at the brighter stars of Canis Major.
Moving onto telescopic observations, the real treasure of Canis Major is the M41 open cluster. Among the easiest of all deep sky objects to locate, simple drop three degrees down from Sirius and you're right at the cluster composed of several dozen blue stars. Although not within the realm of most amateurs, Sirius is actually a binary star. While the actual split, which varies from 3 to 11 arc seconds is not overly difficult on paper, the fact that Sirius A is a blazing -1.4 magnitude while Sirius B (the “Pup”) is a faint +8 makes seeing the companion all but impossible for most people as both superb optics and sky conditions are a must. In fact, Sirius B wasn't actually observed until Alvan Clark spotted it with his new 18 inch refractor, then the world's largest telescope, in 1862. For anyone who lives under very dark sky conditions, Canis Major is located in the heart of the winter Milky Way. While this probably won't be seen visually, the rich star fields will be visible in photos.
In all, Canis Major may not be the most exciting constellation in terms of deep sky objects, but its unique history and prominence of its alpha star more than make it worth a look.
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