‹‹ Looking Up

Chi Cygni Swan Song

Listen Now
2min 00sec

This is “Looking UP! in southern Colorado,” from the Colorado Springs Astronomical Society. I’m Hal Bidlack, and there are lots of reasons to look up!

There are some weird things in the southern Colorado sky, one of the weirdest is the star Chi Cygni, in the constellation Cygnus the Swan. 

Now, we’ve already talked about the two stars that make up the head and the tail of Cygnus the Swan, Albireo and Deneb. Today let’s talk about the star that sometimes makes up the neck, Chi Cygni. And I said “sometimes” on purpose!

If you look at the constellation Cygnus tonight, you can see Chi Cygni as a fairly dim star in line with Albireo and Deneb, toward the Albireo end of the constellation. But if you wait until, say, September 2016, you won’t find it. That’s because Chi Cygni is one of the strangest stars out there.

There are lots of stars that vary in brightness over time. But few change as much as Chi Cygni. Over a period of about 13 ½ months, this star varies in brightness by a factor of 10,000. At its dimmest, it’s far beyond the ability of the human eye to see without a large telescope. But at its brightest, like right now, it is easily observable without any telescope at all.

So what the heck is going on? It turns out the star expands and contracts more than 40% in size during its cycle of brightening and dimming. It’s a huge star – It’s over 470 times larger than our sun. Even at its smallest, if it swapped places with our sun, the Earth would be orbiting inside the star. At its largest, the star would swallow up of Mars and go a good chunk of the way towards Saturn before you got to its surface.

Understandably it’s called a red giant star. Through a telescope you will notice the distinct orange-ish red coloring. Chi Cygni doesn’t have long to live, astronomically speaking, and future astronomers will likely see beautiful expanding bubbles of gas as the star blasts layer after layer of material off into space. It will have a beautiful death, at least for anyone watching from far enough away.

If you’d like to take a closer look at Chi Cygni or any of the other wonderful and amazing things in the sky, please visit KRCC.org or CSASTRO.org for a link to information on our monthly meetings and our free public star parties! 

This is Hal Bidlack for the Colorado Springs Astronomical Society, telling you to keep looking up, Southern Colorado