Observations from Thursday, August 18, approximately 11:00 pm CDT
To the right of the North Star was another familiar sight, a tight group of stars in a zig-zag pattern that has always been described to me as the letter M (or the letter W). Currently, the M is on its side, as you can see from my sketch. To my surprise, I saw a sixth star that messes up the neat pattern of five stars a bit. I guess I’ve thought of these stars as an M for so long that I stopped looking for anything else. Yet there was the sixth star, nearly as bright as the five stars of the traditional M pattern.
These are stars of the constellation Cassiopeia, the mythological queen of Ethiopia, and the M pattern was supposed to represent her reclining on a chair. In the myth, she was punished by the gods for her vanity. But if she was so vain, then why is it that her stars are not as well known as the Big Dipper?
After all, the stars of the M are tightly grouped, bright enough to be seen in the city, and for most of North America, visible all year round and all night long. Once you recognize this pattern in the sky, you will be able to find it easily, pretty much anywhere and any time—just like the Big Dipper. This is because of the M’s position relatively close to the North Star. As the sky rotates around the pole, Cassiopeia never dips below the horizon. And as the summer turns to fall, you will notice that she starts higher and higher in the sky as night falls, until the M actually rotates around and looks like an M again.
It’s really quite a pretty group of stars, and so I think Cassiopeia just needs better marketing in order for more people to recognize her in the sky. She needs a fun and clever nickname that everyone can remember, like the Big Dipper. I suggest “The Zipper,” or maybe “The Fainting Couch.” Or we could just rename her Cleopatra. If you have any suggestions, please leave them in the comments.
The brightest stars in every constellation are given Greek letter names; many stars don’t have traditional proper names.
From top to bottom, the six stars I observed are Beta Cassiopeiae (also known as Caph)–which I will shorten to Beta Cass as an homage to Mama Cass, Alpha Cass (a.k.a. Schedar), Eta Cass (a.k.a. Achird)–my sixth star, Gamma Cass (a.k.a. Tsih by the Chinese), Delta Cass (a.k.a. Ruchbah), and Epsilon Cass (a.k.a. Segin).
As always, check the Log for more facts about these stars.
Another unique feature of Cassiopeia is that these six stars are remarkably similar in brightness. In fact, it was hard for me to tell which of the six was the brightest of the bunch. When I looked up the values, I found that the dimmest star (Eta Cass or Achird, my sixth star) was only about three times fainter than the brightest star. By comparison, the faintest star in the Big Dipper is about four times dimmer than the brightest one.
Which of Cassiopeia’s stars is the brightest? To my surprise, the answer is “it depends.” The star at the center of the M, Gamma Cass, is actually “an eruptive variable star,” which means its brightness changes irregularly. It is currently at its peak, which makes it the brightest of the group. Otherwise, the brightest would be Schedar (second star from the top).
Eruptive variable star sounds exciting, no?
I also found out that Eta Cass, my sixth star, is a star that is of the same class as our own Sun, and it is a relatively close neighbor, just 19 light years away. Eta Cass and our own Sun are very similar in color, temperature, age, and absolute brightness. Unlike the Sun, though, Eta Cass has a companion, a dimmer dwarf star that orbits it about once every 500 years. If we were on a planet orbiting Eta Cass, our Sun would look almost exactly like what Eta Cass looks like from Earth; that was a humbling thought to have on a beautiful August night.
Surely every time I looked up at Cassiopeia’s M, I had seen Eta Cass as well. Yet I did not remember it being there. The sixth star turned out to be the discovery of the evening.
Next: Part 3 of Night One, in which I strain my eyes.
Also see: Part 1 of Night One, in which I write about dark-ish skies, Polaris, and the Little Dipper.