One of the two most basic classifications of material within our own Galaxy, and others.
Population I contains younger stars and clusters, with a more
complex chemistry than stars of the older Population II. Population I stars
are particularly associated with the Galaxy's spiral arms, and
tend to be found along the plane of the Galaxy, as opposed to the Nucleus and the
Globular Clusters, where Population II predominates. Population I
stars are typically hotter and bluer than those of Population II, so that, in common with many other
galaxies, the Milky Way's outer arms
have a bluer hue than its yellow-orange central regions.