Question

Suppose that the physical properties of two stars are identical in every way --- for example, same distance, same mass, same temperature, same chemical composition, and same speed relative to Earth --- except that one star rotates faster than the other. Spectroscopically, how could you tell the stars apart?

Answer 1

By measuring it's Radical velocity using Doppler Phenomenon...

Step-by-step explanation:

It is done by measuring the absorption spectrum produces by a star as a result of measuring Doppler's relative wavelength. The star with the lower speed must have lower absorption spectrum extent as compared to the faster one.