Capella
Published on Dec 15, 2006 at 12:40 am.
2 Comments.
Filed under stars.
Orion is one of the easiest constellations to find, and one that most people know. If you go out this time of year and find Orion in the sky, look to the north of that constellation and you’ll see a pentagon shaped constellation that we call Auriga, the Chariot Driver. The brightest star in Auriga is the star Capella. I created a finder chart using Starry Night Pro software for you. Click on the image to get a full sized view.
Shining at magnitude 0.1, Capella is the sixth brightest star in the sky (or the seventh, if you count the Sun). Capella is a spectroscopic binary star, meaning that it is composed of two stars so close that you can’t see them as a binary star in the telescope, but two sets of spectral lines were found, indicating that there are really two stars there. Both stars are close to the Sun in temperature and color, but they are much larger in size. The Sun is a spectral type G2 star, with a temperature of 5800K. The two stars of Capella are spectral types G2 and G6, about 5900K and 5300K. These two stars are also each a bit over two and a half times the mass of the Sun. Being more massive stars than the Sun, they live shorter lives. Both of these stars are giant stars, eight to ten times the diameter of the Sun. These are stars that have run out of hydrogen to fuse in their cores, and they have left the Main Sequence to be come red giants. They are not there yet, but they are redder than they were. Probably, they were both spectral type A stars like the star Sirius, also visible near Orion. There is also a pair of red dwarf stars that orbit the two bright stars of Capella, making this star really a four star system.
Capella is only a little dimmer than the star Alpha Centauri, the closest star other then the Sun, but while Alpha Centauri is 4.3 lightyears away, Capella is over 42 lightyears distant. That shows how much brighter Capella is than the Sun, because Alpha Centauri is a star very similar to the Sun. But Capella is by no means the brightest shining star out there. It is only a tiny bit brighter than the star Rigel, but Rigel is more than 800 lighyears away, so you can see that Rigel is really a vastly brighter star than Capella.
Most star names that we use today are Arabic, but Capella is one of the few stars with a Latin name (all the constellations are named in Latin, but we use very few Latin names for stars). The Arabic name often given for Capella is Alhajoth, meaning goat. That fits with the Latin, for Capella means little she-goat. The star Capella to the Romans represented Amalthea, the goat that suckled Jupiter in mythology. The early Arabs, though, called the star Al Rakib, the Driver, which makes sense if Auriga is a chariot driver. In India, Capella was known as Brahma Ridaya, the Heart of Brahma. Many English poets referred to Capella as the Shepherd’s Star.
Being rather far north, Capella is up for nearly 18 hours per day here in Texas, but the farther north that you go, the longer it is up. It is circumpolar, meaning that it never sets, for pretty much all of Canada, with the exception of Toronto, which is just barely too far south, but even there it is up for all but a few minutes per day.
I have always rather liked Capella, and I know a few people who regard it as their favorite star. So, go take a look for yourself.
-Astroprof
AntonyM on November 13, 2008 at 7:05 pm: 1
Hello AProf… I just read and reviewed Cormac McCarthy’s “All the Pretty Horses” (I know, it’s about time I got around to reading him) and in a passage I quoted he spelled Capella “Cepella”… P. 60: “…the great diamond of Orion and Cepella (sic) and the signature of Cassiopeia all rising up through the phosphorous dark like a sea-net.”
Don’t know if McCarthy or his publisher in fact made the error.
joey on April 22, 2009 at 1:25 pm: 2
o-m-g you are so smart no way i did not know capella was a STAR!!
ME!! hehe
BYE!