The Milky Way Galaxy

When people ask me what I do, I tell them I study galaxy mergers and evolution. Sometimes they will nod, smile and listen for awhile, and then more often than not, the question will come:  "What exactly is a galaxy?".  I then realize that most people are never taught in school what a galaxy is, and I certainly wasn't before I went to study astronomy at university.  If you are lucky enough to be under a dark, clear sky on a summers night, understanding what a galaxy is becomes so much easier!  (or alternatively, fire up Starry Night at home :) ).

We live within a fairly large spiral disk galaxy, about two thirds from the centre, in one of its spiral arms. During the summer, a faint cloud-like band, known as the Milky Way, arches across the night sky.  If you were in space, far above the Earth, you would see that this band of light actually goes all the way around the sky, forming a great circle around us.  This is because we are inside of the disk of the Milky Way, and the band of light is actually composed of parts of the galaxy which are very far away.  With a telescope, you can see that the Milky Way is composed of millions of individual stars, but to the unaided eye, they all blur together to form a cloud.  You might notice that there are gaps and dark spots in the Milky way.  These are actually massive clouds of gas and dust which block the light from the stars beyond them.

Most of the stars we see in the sky are part of the spiral arm our solar system is located in, known as the Orion arm.  The stars you can see with your naked eyes are like houses in our neighbourhood, while the stars in the other arms are like distant parts of a massive city.  The centre of the Milky Way galaxy is located in the direction of Sagittarius, where a super massive black hole lives.  That black hole is the centre of our galaxy, with all the stars orbiting around it, just like our Sun is the centre of our solar system with the planets orbiting around it, but on a much, much larger scale.  What is a black hole you ask?  We'll look at that in my next post!  For now, make sure you find the time this summer to get out of the city, to a place free from light pollution, and enjoy the view from Earth of our amazing galaxy, the Milky Way!