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More than Meets the Eye

The red in this supergiant is for infrared

The waning moon rises late in the evening at week’s end, cresting the southeast horizon at 9:45 Thursday night, then roughly an hour later each following night. Thursday and Friday the moon travels in good company with Jupiter and the red supergiant Antares of Scorpius.

Thursday evening, the moon rises in the southeast with the scorpion 45 minutes after and with Jupiter behind another 15. Throughout the night, Jupiter and Antares remain 10 degrees apart, roughly the span of your fist held at arm’s length. Antares and the moon begin the evening six degrees apart; by daybreak Friday at 6:07, less than five degrees separate the two.

The two pass during the day, obscured by the sun, so that darkness reveals the moon flanked by red Antares and golden Jupiter. Their distinct colors aside, there’s no mistaking the two: At –2 magnitude, Jupiter outshines first-magnitude Antares sixfold. Little more than five degrees separate star and planet from the moon, and only 10 degrees separate the two from one another, creating an obtuse triangle tight enough to see with binoculars.

But there’s more to Antares than meets the eye. It is far, far away, its light taking more than 600 years to reach our eyes. Put in place of our sun, Antares would appear 10,000 times brighter.

Contrary to what you might expect from a red supergiant, the surface of Antares is cool, about 3,600° Kelvin compared to our sun’s 5,800° K. (Water boils at 373° K.) More than eighty percent of Antares’ light is infrared, invisible to our eyes. Taking that into account, this monster is some 60,000 times brighter than our sun, and its disk would extend nearly to Jupiter.



