Monday, January 05, 2009
Monday Astronomy Minute
This is today's broadcast from Prickly Bay, Grenda. . .
Today, well tonight after about 8 or 9, we turn our attention to the two brightest stars in our sky. The brightest is Sirius also called the dog star as it is the brightest star in the constellation Canis Major. Hard to miss Sirius. Just follow the belt of Orion down to the east. And no wonder it is the brightest star in our sky. . . It is twice as big as our sun and ONLY 9 light years away. nearby!
Now turn your gaze to the south and down a little and the next really bright star you come to is the second brightest star in our sky - Canopus in the constellation Carina. Although it is the second brightest star it is a whopping 300 light years away. What does that tell you? That Canopus is a HUGE and extremely bright star. In fact it is 15,000 times more luminous than our sun.
You’ll notice that both Sirius and Canopus twinkle and show a myriad of colors especially through your binoculars. This is due to the light coming through the atmosphere. Any changes in density and temperature along the way bends the light and bends different colors slightly different amounts just like a prism. This is especially true for stars low in the sky as Sirius and Canopus are as the light has to travel through more atmosphere than a star overhead.
Interestingly, Venus is very bright right now and is low in the western sky but does not twinkle. Why? The reason is that Venus is close enough to be an actual disk rather than a point of light. The various bendings of light from venus all stay within the disk of Venus so we don't see it as twinkling
Thanks to Kevin on Exodus for getting me to research Canopus!
Those of you north of 38 degrees latitude. . .don't bother looking for Canopus. It never rises above your horizon. Sorry!