How the Milky Way … In one calculation, the Milky Way has a mass of about 100 billion solar masses, so it is easiest to translate that to 100 billion stars. Population I The disk of the Galaxy is thought to be about 10 Gyr old. An elliptical galaxy contains a mixture of Population I and Population II stars within the body. Lecture 22: The Milky Way.

It tickles me that we know the shapes of galaxies hundreds of millions of light years distant with much more specificity and confidence than we know our own Milky Way. The fundamental difference between these two types relates to when and how they were formed. Elliptical galaxies have eight subclasses E0-E7, where eccentricity increase in the direction of E0 to E7, and E0 is roughly spherical in shape. Young, metal rich stars rotating with the disk of the Galaxy are termed Population I, while old, metal weak stars are termed Population II. By the way, this is a very interesting report about important and innovative research.

What is the difference between Spiral and Elliptical … The luminosity of the Milky Way galaxy according to this is $5\times10^{36}$ Watts, but this number suggests that there are about 10 billion stars with Solar luminosities in the Milky Way, which doesn't sound right considering that the Milky Way contains 200-400 billion stars of different luminosities.. Detailed Shape of the Milky Way-- comparison of various views of the Milky Way with external galaxies suggests strongly that the Milky Way is a spiral galaxy . Younger, metal-rich stars, a.k.a. Etc. Milky Way as seen by the Cobe satellite in the near-infrared. NGC891 . Population II stars are older than Population I stars.

Population I stars, are found in the disk. Older stars, a.k.a.

The same goes for Andromeda, it has a luminosity similar to the Milky Way with even more stars. Stars observed in galaxies were originally divided into two populations by Walter Baade in the 1940s. Population II stars, are poor in metal and are found in the halo and the central bulge.