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Arcturus, the "golden" Bear Watcher

Last night the clouds parted for only two hours, so I quickly got out my telescope and hopped along a few deepsky objects. M3, M5 and M13 looked great but for me the most impressive object last night was Arcturus, the fourth-brightest star in the sky, and the brightest star north of the celestial equator.

Arcturus is a a really beautiful, magnitude -0.3 star, with a lovely golden-yellow colour.  Its spectral type is K1 and its surface temperature is 4.300 degrees Kelvin. This giant is about 37 light years away from us and has a diameter 25 times the diameter of the Sun. If it would replace our Sun, Arcturus would appear 12 degrees across in the sky (which Coronado would you need to capture the whole disk into the field of view?). 

Arcturus can be found at the tip of the big kite shaped constellation of Bootes.

image
Image from SkyTools 2 by CapellaSoft

Arcturus, or the “Guardian of the Bear”, follows the Great Bear (Ursa Major) across the night sky. The name Arcturus comes from the Greek “arktos”, meaning bear and our word “arctic” that references the Bear’s northerly position. (Kaler, The Hundred greatest Stars p.21) While observing Arcturus I realized that a single bright and colourful star against a black background can be as beautiful and spectacular as any other deepsky treasure. Be sure to pay Arcturus a visit the next time you’re observing! Take your time for a closer look.

Posted by Math on 05/10 at 02:04 PM
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