09 February 2012

Auriga and Capella: the Galactic Anticenter

High overhead in the winter sky is the distinctive constellation Auriga the Charioteer. This is a bright constellation, visible even with city lights, punctuated by the 6th brightest star in the night sky, Capella. To the casual viewer, Auriga appears to be a pentagon in the sky, and in winter it is nearly directly overhead as night sets in. Depending upon the source, the constellation Auriga is described as the actual Charioteer holding a goat, or just the shape of his pointed  helmet. The star name Capella is in fact Latin for 'small goat.'

Auriga has the distinction of being located in the direction of the Galactic Anticenter. What is an anticenter? It is the point in the night sky that is opposite the Galactic Center, of course :-)  The center of the Milky Way Galaxy is located in the direction of the constellation Sagittarius, a dominant summertime constellation. So not surprising, in the winter time when we are looking the 'other direction' in the sky, we find ourselves staring out into space directly out of our Milky Way Galaxy.

The bright star Capella is relatively close to Earth, 42 light years away. It shines brightly in the winter sky, making Auriga easy to locate. A fascinating fact is that the star Capella is not one star, but a four-star system made up of two binary stars. That means, that the four stars are broken into two pairs of binary star systems. Two of them are big stars, 10 times the size of our Sun. The other two are quite small and faint, so when you see Capella you are primarily seeing the two bigger stars. Some binary star systems can be seen as separate stars in small telescopes or binoculars, but the two bigger stars in the Capella system are too close to see as separate objects.

Try to locate Auriga and Capella tonight and savor the fact that you are staring out of the Milky Way into the vastness of space far away from our home galaxy.


peter parsons said...

maybe this is why when i sing 'a capella' my sons say i sound like a bleating goat. ba dump bump.

but seriously, the 'the opposite of the center' of our galaxy is just looking away from it? like, anywhere but at the center? that is, 'a' is not 'not a' and therefore is its opposite? just a bored question. great post paul.

The Urban Astronomer said...

Hey there Peter - Never thought about the term a capella being related to the goat. I'll try that out at star parties in the coming weeks.

The opposite means precisely in the opposite direction of the Galactic Center. not just looking generally the other way, but looking precisely the other way, out of the Milky Way. Of course, there are still 20,000 light years of Milky Way in that direction but the view is the shortest distance anywhere in the path of the Milky Way to the edge of the galaxy.

Come to think of it, looking above or below the plane of the Milky Way takes a lot less effort and yields the same result, but that's much less exciting to write about ;-)

-- Paul

Sidewalk Universe said...

Wonderful perspective bro! Super post!

The Urban Astronomer said...

Thanks for the nice comment, Richard. Just raising the awareness of the big night sky -- like you do so well!

-- Paul

Anonymous said...

Not to nitpick, but consider the words 'above' & 'below' with respect to the galactic plane. I realize this is a convention--'above' being the same side as Earth's North Pole (right?). Here in a gravity well, I can say the floor is below me b/c it's nearer to the center of the Earth, but in intergalactic space? Just shows how our environment affects our language and maybe even our understanding of things.

The Urban Astronomer said...

Hey there Anonymous - good point.

When I talk about the sky at star parties, I try to point out our location in the universe and general coordinates such as "in the direction of Sagittarius" or "in the other direction, toward Auriga" work pretty well for helping people to visualize things. Good thing I am not a research scientist ;-)

-- Paul

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