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Blue Beauty

February 25, 2018

Eighteenth-century astronomer William Herschel described the star system known as Beta Monocerotis as “one of the most beautiful sights in the heavens.” It’s one of the hidden beauties of Monoceros, the unicorn. The constellation is well up in the southeastern sky in early evening, between two bright stars: the “little dog” star Procyon, and Betelgeuse, the orange shoulder of Orion.

There’s not much to see in Monoceros with the eye alone. But telescopes reveal a bounty of beautiful sights. And Beta Monocerotis straddles both domains. It’s faintly visible to the unaided eye as one of the unicorn’s two brightest stars. But to see the same beauty that Herschel did, you need a telescope. That view reveals three stars, not one, all with a lovely blue-white color.

The color comes from the temperatures of the stars — their surfaces are many thousands of degrees hotter than the Sun’s. And all three stars also are much more massive than the Sun. That great heft revs up the nuclear reactions in their cores, which is what makes their surfaces so hot. It also makes the stars extremely bright — up to about 3200 times as bright as the Sun. That makes them visible across 700 light-years of space.

The two faintest members of the system probably form a wide binary, with the brightest of the three stars orbiting around them. Combined, they make Beta Monocerotis a beautiful skywatching sight — a vision in blue on a chilly winter’s night.

Script by Damond Benningfield

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