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Blue-white Rigel is at the foot of Orion

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Tonight for February 16, 2015

Up before the sun? See the moon and Mercury before sunrise February 17, 2015

On February 14, we talked about Orion’s bright star Betelgeuse. Tonight … its bright star Rigel.

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!

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 today’s chart. Look back at yesterday’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. (Try binoculars, if you can’t distinguish color with the unaided eye.) Betelgeuse has a reddish hue, while Rigel sparkles blue-white. By the way, a star’s color is very 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!

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It'll be a big challenge, especially at norterly latitudes, to catch the moon and Mercury before sunrise on February 17. From the Southern hemisphere, the moon and Mercury will be infinitely easier to see before sunrise.

It’ll be a big challenge, especially at northerly latitudes, to catch the moon and Mercury before sunrise on February 17. From the Southern Hemisphere, the moon and Mercury will be infinitely easier to see before sunrise.

See Mercury in the sunrise direction on February 17, 2015. The planet Mercury – innermost planet of the solar system – is up in the east before sunrise on these February 2015 mornings. Many people never see Mercury because it stays near the sun in our sky. To catch it, though, look east and close to the sunrise point on the horizon 75 to 60 minutes before sunrise. Binoculars may be helpful. This particular apparition of Mercury in the morning sky greatly favors the Southern Hemisphere.

Bottom line: This post describes how to locate Orion’s bright blue-white star Rigel. Plus … try finding Mercury before sunrise on February 17, 2015.

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