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January 16, 2016

If you’re a mighty Greek hunter who’s tired from being out with the dogs all day, then it probably feels pretty good to put your feet up. And fortunately for the celestial hunter, the people who drew the early constellations provided a convenient footstool.

Orion, the hunter, is well up in the east and southeast as night falls. Look for his three-star belt aiming almost straight up from the horizon. His foot is to the right of the belt — the blue-white star Rigel. A fainter star stands just above Rigel. It’s known as Cursa — a name that means “the footstool of the Central One” — the Central One being Orion himself.

Yet the footstool doesn’t belong to the constellation Orion at all. Instead, it’s one of the brighter lights of Eridanus, the river, a long, faint streamer of stars that meanders far to the right and lower right of Orion.

Cursa is about 90 light-years away — a good bit closer than Rigel. It’s roughly twice as big and heavy as the Sun. And it’s classified as a stellar giant. That means it’s used up the original hydrogen fuel in its core, causing its outer layers to begin puffing up like a balloon.

Over time, it’ll ignite a new series of nuclear reactions, which will make it get much bigger than it is now. It’ll also get much brighter, and it’ll get cooler, which will make its surface shine yellow, then orange — making the footstool as impressive as the foot it’s there to support.

We’ll talk more about the river tomorrow.

Script by Damond Benningfield, Copyright 2015

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