The Sun is orbiting inside the thin disk, within 3K light years of the galactic plane, where most of stars and most new stars reside (other than the center bulg

The Sun is orbiting inside the thin disk, within 3K light years of the galactic plane, where most of stars and most new stars reside (other than the center bulge or bar). http://en.wikipedia.org/wiki/Thin_disk http://en.wikipedia.org/wiki/Thin_disk Star ages can be estimated by their composition (older stars contain more helium), color (bluer stars live far shorter than redder stars), brightness for their given color (older stars burn brighter), activity (younger stars are more active, they flare more) and if they contain protoplanetary disks (a feature of very young stars). Astronomers also use the HR diagram: http://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_diagram http://en.wikipedia.org/wiki/Hertzsprung%E2%80%93Russell_dia... Having a good measure of distance is important and there are various ways to determine that: http://en.wikipedia.org/wiki/Cosmic_distance_ladder http://en.wikipedia.org/wiki/Cosmic_distance_ladder