Moon and Aldebaran

Moon and Aldebaran

There are several ways to judge the brightness of a star. And a star that appears close to the Moon late tonight illustrates all three.

Aldebaran marks the orange eye of Taurus, the bull. It’s close to the lower right of the Moon at first light. A brighter orange light is farther to the upper right: the planet Mars.

The first way to judge Aldebaran’s brightness is apparent magnitude. That’s how bright it looks in our sky. On that scale, it’s at about point-eight-six — the 14th-brightest star system in the night sky.

The second way to judge its brightness is absolute magnitude. That scale compares how bright stars would appear if they were all lined up at the same distance from Earth: 32.6 light-years. That’s exactly half the distance to Aldebaran. So when you do the math, you get an absolute magnitude of minus-point-six-four. That means Aldebaran really is a bright star.

Stars produce a lot of light other than the form that’s visible to the human eye. The surface of Aldebaran is fairly cool, so it produces more infrared light than visible light. Combining all the wavelengths provides the star’s luminosity. On that scale, Aldebaran is about 440 times the brightness of the Sun. Still, it’s not nearly the brightest light out there. The most intense stars yet seen shine millions of times brighter than the Sun.

Even so, Aldebaran is probably in the top one percent on the list of bright stars.

Script by Damond Benningfield

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