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October 18, 2015

One of the largest constellations soars overhead on autumn nights. And one of its highlights is a giant star that’ll end its life with a titanic explosion.

Pegasus, the flying horse, stretches far across the sky. As night falls this evening, its body is well up in the east, with its head and forelegs even higher in the southeast.

Its most distinctive feature is a wide pattern of four moderately bright stars — the Great Square — which outlines the horse’s body. The horse’s nose — the star Enif — stands to the upper right of the Great Square.

Enif is a remarkable star. It’s much more massive than the Sun, so it burns through the nuclear fuel in its core at a furious rate. That makes the star shine brilliantly — it emits more light in a single minute than the Sun produces in four days.

Enif once generated energy as the Sun does, by fusing hydrogen to make helium. Unlike the Sun, though, it shined a brilliant blue. But the star’s core quickly ran out of hydrogen, so it started fusing the helium to make even heavier elements. As a result, the star’s outer layers expanded and cooled. So today, Enif is an orange supergiant. It’s so big that if it took the Sun’s place, it would swallow Mercury and possibly even Venus.

Eventually, the star will no longer be able to produce nuclear reactions. When that happens, Enif will explode — briefly giving Pegasus a nose that looks more like that of a certain well-known reindeer than a flying horse.


Script by Ken Croswell, Copyright 2015

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