Sky ArchiveTonight

Blue-white Rigel at Orion’s foot

Rigel is one of Orion's two brightest stars.  The two are located on either side of a short, straight row of three medium-bright stars - Orion's Belt.
Rigel is one of Orion’s two brightest stars. The two are located on either side of a short, straight row of three medium-bright stars – Orion’s Belt.

Tonight … look for the bright, blue-white star Rigel in the constellation Orion the Hunter.

Before you can find Rigel, you need to know how to find Orion. The three sparkling blue-white stars of Orion’s Belt are easy to spot. As viewed from the Northern Hemisphere, this compact line of stars can be found in the south to southeast sky at nightfall. It is more toward the northern sky for observers in the Southern Hemisphere.

No matter where you are, if you look outside in the evening now, chances are the pattern you’ll pick out will be Orion! Yes, it really is that noticeable.

You might 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 the chart at the top of this post. Click here to see a chart showing 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. Try binoculars, if you can’t distinguish color with the unaided eye. Betelgeuse has a reddish hue, while Rigel sparkles blue-white.

A star’s color is revealing of its surface temperature. Red stars are cool (2,000 to 3,500 Kelvin) and in the autumn of their years, while blue and blue-white stars are hot (over 10,000 K) and young, in the heyday of youth.

Astronomers believe both red and blue supergiant stars blow up into supernova explosions, though at one time it was thought that only red supergiants did so.

Look for Rigel, Orion’s blue supergiant star, at the foot of Orion tonight!

Bottom line: This post describes how to locate Orion’s bright blue-white star Rigel.

Read more: Somber Betelgeuse in Orion’s shoulder

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February 12, 2018
Sky Archive

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