Milky Way Galaxy - our celestial backyard
On dark, clear nights we can sometimes see a faint, hazy band of light studded with many stars and stretching across the sky. This is the body of the Milky Way, the galaxy in which we live. Here in the southern part of Australia, the centre of the Milky Way passes almost directly overhead so we can obtain an excellent view of our galaxy.
Our understanding of the Universe has changed vastly over the last 400 years. The Earth is no longer regarded as the centre of the Universe. Now we know that we are like "suburban residents" of the Milky Way, situated well away from the centre of the galaxy. Our solar system is about 30,000 light years out from the galactic centre and orbits around it at a speed of 250 kilometres per second. The astronomer Harlow Shapley, in the 1920s, was the first to realise that we are not at the centre of the Milky Way.
Containing over 100 billion stars (some of which may have planets!), and different types of interstellar gas and dust, the "body" of our galaxy is shaped like a great disc 300 light years thick and 100,000 light years across. It is a spiral galaxy, and our Sun is about two thirds of the way out from the centre along one of the spiral arms. Humans like to think they are important; but in the vastness of the Milky Way, our Earth is like a grain of sand on the beach - and the Milky Way is only one of millions of galaxies wheeling through space!
