1. Lecture 18 – October 8, 2003 How We Determine Masses of Stars
Method:observation of binary stars (double stars)

2. Binary stars are numerous (e.g. Sirius)

3. We can see orbital motion of Sirius B around Sirius A

4. Masses of stars determine the gravitational force, and thus the acceleration of the stars

5. A little gravitational physics
If M >>m
V2 = GM/r
Or M=V2r/G
From observations of motions of binary stars, one can determine their masses

6. The Types of Binary Stars
Visual Binaries
Eclipsing Binaries
Spectroscopic Binaries

7. Eclipsing Binary Stars (like Algol)