An all-sky photograph reveals the Milky Way stretching from horizon to horizon. We cannot see much of our own galaxy from our position inside it.
Clouds of dust block our view.
Photographs taken from Earth can explore only about 10 percent of our galaxy, but that is enough to tell us what it is like and to hint at its history. The key to understand our galaxy is the separation of its stars into two regions. Most stars, including the Sun and all the gas and dust, lie in a thin, rotating disk. Some stars and star clusters, however, are scattered through a spherical volume that completely encloses the galactic disk. The motions, compositions, and ages of the stars in these two regions can help us visualise the formation of our galaxy.