Milky Way

The galaxy we live in is called the Milky Way. Because we live inside it, it is hard to see its shape. From Earth, we see a faint, white band stretching across the night sky. The name comes from the Latin words meaning "milky path". Looking closely at this band, we see that it is made up of billions of stars. A lot of the light coming from those stars is blocked by gas and dust in the galaxy. It is this gas and dust which will ultimately form new stars.

Hubble Tuning Fork
Full-sky composite image of the Milky Way Galaxy
  Credit: Gigagalaxy Project

Telescopes have accurately measured the positions of stars and found that the Milky Way is a barred spiral galaxy. It has over 200,000,000,000 (200 billion) stars inside it. It is disk shaped with a bulge in the middle. The Milky Way is about 100,000 light-years across and 1000 light-years thick. The Sun is on one of the spiral arms of the Milky Way, two-thirds of the way out from the centre.

In the same way that the Earth orbits the Sun, the Sun orbits the centre of the Milky Way. It travels at a speed of almost 220 km/s. Even at this speed it takes our Sun around 225 million years to complete one full orbit of the galaxy.