The Milky Way and our galaxy

If you look up on a clear night far from city lights you will see a faint, fuzzy band of light crossing the night sky from near the constellation of Scorpio, through Cygnus, Cassiopeia, Perseus and towards Canis Major. This is what we call the Milky Way.

The true nature of the Milky Way puzzled observers of the Night Sky for centuries until in the sixteenth century astronomers looked at it through a telescope. They saw that it was not just a fuzzy band but was made up of thousand upon thousands of stars. Photographs taken with one of today's large telescopes show it containing many millions of stars. Even quite a small telescope will show many stars - the photograph shows part of the Milky Way in Perseus taken with a 200 mm reflector.

However it was not until the twentieth century that astronomers realised what the Milky Way really was. When we look at the Milky Way we are actually looking through our galaxy.

If you read the file called Galaxies in the 11-14/ Astronomy/Text section you will understand that our galaxy is a huge spiral structure of some 100 000 million stars, 100 000 light years across and with the Sun about two thirds of the way from the centre in one of the arms of the galaxy. When we look at the Milky Way we are looking across the galaxy and that is why we see so many stars. Turn at right angles to this direction and we would be looking out from the galaxy into deep space.

The shape of our galaxy is rather like the shape of two plates put face to face (Figure 2). The diagrams show first the face of the galaxy and then edge on (Figure 3 (a) and (b).




The red arrow shows the direction towards the centre of the galaxy. If you looked in this direction you would see very many stars – this is the Milky Way. Looking at right angles to this, the blue arrow, you would see far fewer stars as you would be looking out of the galaxy into deep space.

The two photographs are galaxies similar to our own galaxy but again one is taken showing the face of the galaxy and the second edge on.