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Earthsky Tonight, February 4, 2010: Blue-white Rigel is at the foot of Orion
Posted By Gary Wamsley On February 5, 2010 @ 4:40 pm In Earth & Sky | Comments Disabled
Courtesy of EarthSky
A Clear Voice for Science
The three sparkling blue-white stars of Orion’s Belt are easy to spot. As viewed from this hemisphere, this compact line of stars can be found in the southern sky at nightfall. Look in the south to southwestern sky any evening around now. Chances are the pattern you’ll pick out Orion!
You may note that Orion’s two brightest stars – Betelgeuse and Rigel – lodge at an equal distance above and below Orion’s Belt. Rigel  is shown on today’s chart. Look back at Wednesday’s chart  to see Betelgeuse.
Look again at Rigel. Because it lies some 775 light-years  away, Rigel must be intrinsically extraordinarily luminous to shine so brightly in our sky. If this star were as close as our sun, it would outshine the sun by 40,000 times!
Although both Rigel and Betelgeuse are extremely luminous supergiant suns, the stark color contrast between these two stars makes Betelgeuse and Rigel readily distinguishable. Betelgeuse has a reddish hue, while Rigel sparkles blue-white. By the way, a star’s color is very revealing its surface temperature. Red stars are cool (2,000 to 3,500 Kelvin ), while blue and blue-white stars are hot (over 10,000 K).
Astronomers believe both red and blue supergiant stars blow up into supernovae explosions, though at one time it was thought that only red supergiants did so.
Written by earthsky
Space Com 
Amazing Space 
Scope City 
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URLs in this post:
 www.EarthSky.org: http://www.EarthSky.org
 Image: http://www.earthsky.ord
 Rigel: http://www.earthsky.org/tonightpost/brightest-stars/blue-white-rigel-is-orions-brightest-star
 chart: http://www.earthsky.org/tonighthome/2010-02-03/url
 light-years: http://www.earthsky.org/tonightpost/astronomy-essentials/how-far-is-a-light-year
 Kelvin: http://www.biochem.northwestern.edu/holmgren/Glossary/Defintions/Def-K/kelvin.html
 Sky and Telescope: http://www.skyandtelescope.com/observing/ataglance/
 National Geographic: http://news.nationalgeographic.com/news/
 Space Com: http://www.space.com/nightsky/
 Amazing Space: http://amazing-space.stsci.edu/tonights_sky/
 The York County Astronomical Society: http://www.ycas.org/tonights_sky.htm
 Scope City: http://www.scopecity.net/
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