Page 18, The Stars I: [Previous Page] [Next Page] [Lecture Notes] [Class Home Page]

If we are very lucky, the stars lie in a flat plane, and pass in front of each other once or possibly twice each orbit (an eclipsing binary):

When ever one star passes behind its binary companion, its light is lost and the entire system appears to dim. Careful study of these 'Light Curves' can reveal information about the relative radius of the stars.

If we are able to determine the size of the orbit, we can solve directly for the exact masses of the two stars using Kepler's 3rd Law. Here, m and M are the masses (in Sun Masses) of the two stars, a is the average distance between the stars (in A.U.), and P is the period (in years) of their orbit.

Binary stars with masses 2 M_o and 3 M_o, have a period of 3 years. What is the average distance between the two stars?