File:Guide to our Galaxy

Description
This virtual journey shows the different components that make up our home galaxy, the Milky Way, which contains about a hundred billion stars.

It starts at the black hole at the centre of the Milky Way and with the stars that orbit around it, before zooming out through the central Galactic Bulge, which hosts about ten billion stars.

The journey continues through a younger population of stars in the stellar disc, home to most of the Milky Way's stars, and which is embedded in a slightly larger gaseous disc. Stars in the disc are arranged in a spiral arm pattern and orbit the centre of the Galaxy.

The discs and bulge are embedded in the stellar halo, a spherical structure that consists of a large number of globular clusters -- the oldest population of stars in the Galaxy -- as well as many isolated stars. An even larger halo of invisible dark matter is inferred by its gravitational effect on the motions of stars in the Galaxy.

Looking at a face-on view of the Galaxy we see the position of our Sun, located at a distance of about 26 000 light-years from the Galactic Centre.

Finally, the extent of the stellar survey conducted by ESA's Hipparcos mission is shown, which surveyed more than 100 000 stars up to 300 light-years away from the Sun. In comparison, ESA's Gaia survey will study one billion stars out to 30 000 light-years away.