The River

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 — from a longer 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. It’s a long, faint ribbon of stars that meanders far to the right and lower right of Orion.

Cursa is about 90 light-years away — much closer than Rigel. It’s roughly twice as big and heavy as the Sun. And it’s classified as a stellar giant. 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. All of those changes will make the footstool even more impressive than the foot it’s there to support.
 

Script by Damond Benningfield