The Milky Way and Beyond

Tonight is the last night of the astronomy course that I mentioned in the previous post. Guess what? It's raining, and it will be an indoor lecture again tonight. This is all well and good, but I really need to know more about how to look at the stars. Ah well, maybe I'll try again in the spring.

As I rambled on and on last time, I ran out of time and space to post more information about our galaxy itself, so I thought I would share a few facts. I realize that most already know them, but what the heck.

I posted this graphic last time, but it reviews some basic information about The Milky Way: that the diameter is 100 000 light years, for example. It is of disc or elliptical shape, with a bulge in the middle and with arms spiralling outward from the centre. Our sun and, therefore, the earth and the whole solar system is located on one of these outer arms, quite a distance from the centre.

Best estimates estimate that The Milky Way contains at least 200 billion stars and perhaps as many as 400 billion. That's billion, not million. Now consider that there are galaxies that are much larger with the largest that we know of perhaps containing more than a 100 trillion stars. Now consider that there are perhaps 100 to 200 billion galaxies, with some astronomers estimating even more. I don't know about you, but those facts don't mean much to me other than the fact that the universe is essentially infinite.

The profile view to the right shows that our solar system is located about 28 000 light years from the galactic centre. It also shows that the arms are quite thin. Estimates seem to suggest that most of the galaxy might only be 1-3 light years thick. The Central Bulge may by 10 000 light years thick.

In both diagrams it is also apparent that there is much stuff around the galaxy. These are 150 known globular clusters and even small satellite galaxies as it were.

Beyond this, The Milky Way is part of a cluster of a local group of about thirty galaxies, the closest of which is Andromeda. In turn, our local group is part of what is known as the Virgo Supercluster, which is thought to contain 100 groups and clusters.

All of this is in motion. We know that the earth both rotates and revolves around the sun, but the sun also rotates once around the galactic center every 200 million years. Of course, the galaxy itself is also hurtling through space at an estimated velocity of ~600km/sec.

It's time to stop and give my head a rest from trying to deal with these incomprehensible statistics. I will close with this picture of another spiral galaxy, which is thought to be of similar shape to our Milky Way. I should have noted the particulars at the time that I downloaded it, which galaxy it is, but alas ... I didn't.