When viewed through a telescope, the Milky Way turns out to be a region containing millions of faint stars seemingly packed close together. This is because when we look at the Milky Way, we are seeing a cross-section of our own Galaxy. The stars really far apart. They just appear to be close together because of the way we view them from the Earth.
The Galaxy takes the form of a flattish disc with a bulge
(nucleus) in the middle. The 100,000 million stars it contains are spread
out on the disc. In practice, the stars in the disc group together on arms
that spiral out from the centre. The whole Galaxy rotates around the centre,
but not at a uniform speed. Stars at the centre travel faster than those
farther out. The Sun (30,000 light-years from the centre) takes 225 million
Earth-years to make one rotation. This period of time is called a cosmic
year.
Spot facts:
| The halo that surrounds our Galaxy may itself be surrounded by a "dark halo" of invisible matter. It could extend more than 200,000 light years from the Galaxy's centre. |
