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Christmas Skies

December 25, 2017

We’re already several days into winter, but the signature star pattern of summer remains in good view in the evening sky. And one of its members does double seasonal duty — it anchors one of the signature star patterns of early winter.

The Summer Triangle is in the western sky as night falls. Its three points are Vega, the brightest member of the group, which forms the right point of the triangle; Altair, the left point; and Deneb, at the top of the triangle.

Although Vega looks brightest, Deneb is intrinsically brightest. In other words, if you lined up all three stars at the same distance from Earth, Deneb would outshine the other two, and by a wide margin: Altair is about a dozen times brighter than the Sun, Vega about 40 times — and Deneb as much as 200,000 times.

In fact, Deneb is one of the biggest, brightest stars in the entire galaxy — a monster that’s a couple of hundred times wider than the Sun. It’s also quite hot, so it shines blue-white. And someday, it’ll get even brighter — it’ll blast itself to bits as a supernova.

For now, though, Deneb marks the tail of Cygnus, the swan. At this time of year, the swan is diving toward the western horizon nose first. At that angle, its body and outstretched wings look like a crucifix, giving Cygnus a second name: the Northern Cross. Deneb serves as both the tail of the swan and the top of the cross — a bright star that’s beautiful no matter which way you look at it.


Script by Damond Benningfield

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