ABSTRACT
The Sun is one of around 100000 million stars making up our Galaxy. The system is often referred to as the Milky Way galaxy, but the term ‘Milky Way’ is usually restricted to the luminous band stretching across the sky. There is a main disk, around 100 000 light-years in diameter; the disk is 2000 light-years thick. The disk is made up chiefly of young objects, and star formation; the halo consists of older Population II objects, and the star-forming material has been used up. As well as stars, the Galaxy contains a vast amount of thinly-spread interstellar matter. The Galaxy is a spiral system, classed officially as of type Sbc. ‘Density waves’ sweep around the Galaxy, and produce what may be called cosmic traffic jams, compressing the material and triggering off star formation. The Galaxy must be regarded as a large system, although it is in no way exceptional.
