Stellar Populations

Population I Population II
Extreme Intermediate Intermediate Extreme
Location spiral arms disk bulge halo
Metals (%) 3 1.6 0.8 less than 0.8
Shape of orbit
(see below)
circular, in galactic plane slightly elliptical in galactic plane moderately elliptical, extending out of galactic plane highly elliptical, not confined to galactic plane
Average age (yr) 100 million and younger 0.2-10 billion 2-10 billion 10-14 billion