Size & Shape

- Demonstrate an understanding of the size and shape of our Galaxy and the location of the Sun, dust, sites of star formation and globular clusters
- Recall that the Milky Way is an Sb type galaxy

Understanding what our galaxy looks like is difficult as it is like making a drawing of your house if you have only ever been on the inside and never seen it from outside. We notice a few things from other galaxies that give us clues.

There is a plane, or disc about 1,500 light years thick. There are spiral arms that make up this plane.

The plane from one end to another is between 100,000 to 150,000 light years across.

Also there is a central bulge in the centre. This is in the region of Sagittarius, but we cannot see it very well because there is a lot of cosmic dust in the way. We can however detect it with infrared and radio signals.

At its centre is believed to be a supermassive black hole called Sagittarius A which is a source of immense radiation which we can detect.

Globular clusters surround the halo - the dusty area around the galaxy. Star clusters are positioned near the arms.


Type of Galaxy

The Milky Way is an Sb (Spiral barred) galaxy. Until recently it was considered a spiral galaxy.


  • Descibe the type of galaxy the Milky Way is.
  • Describe the location of the Sun in the Milky Way
  • What is the width of the Milky Way in light years?
  • What is its height along the plane?
  • What is thought to be at its centre?
  • Where are star and globular clusters positioned with respect to our galaxy?