Milky Way Galaxy Star populations and movementastronomy

The concept of different populations of stars has undergone considerable change over the last several decades. Before the 1940s, astronomers were aware of differences between stars and had largely accounted for most of them in terms of different masses, luminosities, and orbital characteristics around the Galaxy. Understanding of evolutionary differences, however, had not yet been achieved, and, although differences in the chemical abundances in the stars were known, their significance was not comprehended. At this juncture, chemical differences seemed exceptional and erratic and remained uncorrelated with other stellar properties. There was still no systematic division of stars even into different kinematic families, in spite of the advances in theoretical work on the dynamics of the Galaxy.