## Using v=d/t to find diameters of stars

### The geometry of the eclipsing X-ray binary problem

To simplify the problem, we make two assumptions when we use this method:

- The orbit of the X-ray emitting star is circular and its
velocity is constant.
- The orbit of the observed star is large and the system is
distant, so that light rays from the source are parallel.
- The plane of the binary system is at 90 degrees, edge on to our line of sight. (The actual orbit is at 83 degrees.)

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