053.3 Where the Stars Are

The traditional classification of stars in our galaxy is:

• Population I: Stars closely related to our Sun.
• Population II: Very old stars not much like our Sun.

Population I stars are mostly found in the disk and include many short-lived bright type O and B stars as well middle-aged stars such as our sun.

Population II stars are mostly found in the halo and are all extremely old.

As usual, the traditional terminology is confusingly backwards: Population II came before Population I.