Hey, Sky Fans!
A couple of weeks ago, I mentioned the southern constellation Crux, the Southern Cross. “Mentioned” is one way of phrasing it. Swooning might be another.
We also talked about a star called Rigil Kentaurus. I said that it’s the star we often call Alpha Centauri; the closest star system to home. It’s not surprising that stars would have different names. Different cultures call things by different names all the time. That’s not surprising. Also, astronomers have a few catalogs they use for keeping track of stars and other objects. That name, though, is an interesting one.
Many years ago, when I first heard the name Rigel Kentaurus, also Rigil Kent, I got confused with Rigel, the, sometimes, brightest star in Orion. I say “sometimes” because Betelgeuse is a variable star, and it sometimes outshines Rigel, sometimes not. After a little while of looking at sky charts and maps, I had one of those aha! moments (Not an A-Ha moment; those kind of ended when I was in grade school. Isn’t “Take on Me” still a terrific song, though?).
Someone hit the music!
A star’s Bayer Designation is a name given to it that uses a Greek letter and the Latin name of the constellation it’s in to collect and rank stars by their brightness. A constellation’s “Alpha” star is generally it’s brightest. The “Beta” star is the second brightest. The third brightest, the “Gamma” star, and so on. The 16th brightetst star in a constellation would be the Pi star. The system was developed in the 1600s by the German astronomer Johann Bayer.
There are times when things get a little goofy, and the ranking gets a little out of order. The second brightest winds up as the Alpha star and the brightest as the Beta, but all in all, that’s the system.
Take Orion. Betelgeuse is considered its brightest star, so its Bayer Designation is Alpha Orionis. Rigel, the second brightest, Beta Orionis. Bellatrix, the hunter’s right shoulder, Gamma Orionis. See the pattern? For another example, Alpha Aurigae is Capella, the brightest star in Auriga.
Let’s head back to Alpha Centauri and Rigel Kentaurus. Rigel comes from Arabic, and means foot, or leg. Orion’s Rigel is its left foot. Past that, though, I think it’d be hard to deny there’s a definite, real similarity happening between “Centauri” and “Kentaurus.” These are different forms of the name of the southern constellation Centaurus.
I’m not going to pretend to know Latin, but the Bayer names use the genitive form of the constellation’s name; essentially its possessive form. This means “Alpha Centauri” means “Centauri’s Brightest Star.” So, we haven’t been calling it by a name, as much as just saying it’s the brightest star in its constellation. Aha!
A few months ago, in November 2016, the International Astronomical Union (IAU) cleared up the names of over 200 stars. Among them, Rigil Kentaurus became the official name of Alpha Centauri. Between you and me, I might just keeping calling it by what I learned while I was listening to my A-Ha records.
What about Crux, though?
This picture, fresh off the astroeasels down at Sky Watch’s art department has a drawing of the southern cross. Get a load of those star names.
Acrux? Becrux? Gacrux? What the what? That’s right. I’ll say it: I love these names, and I also love portmanteaus. Don’t get me wrong. I love the poetry, mythology and history behind some of the older and exotic-sounding names for loads of other stars. Can you really argue with names like Zubenelgenubi (Alpha Librae) and Zubenelschamali (Beta Librae)? No, you’re right, you can’t. These Crux names just tell it like it is, though.
Acrux is Alpha Crucis; Crux’s brightest star). Becrux (intoxicatingly enough, officially called Mimosa) is Beta Crucis; second brightest. Gacrux is Gamma Crucis; third brightest. Good stuff. Nerdy, but good.
These sorts of astronomical bookkeeping posts might seem sort of clunky, especially when I write them, but the Bayer system is really handy to me. It’s really helpful to look up at the sky, see something, and be able to say “Oh, yeah, Denebola is Leo’s second brightest star,” as people hurry across the street.
Catch up with you a little later. Clear skies, everyone!