In: Physics
Explain why the temperature of star is related to the broadening of a spectral line from the star and if a broader spectral line indicates a cooler or hotter star.
If the temperature of a star (or in general any object) is high,
the average kinetic energy of the molecules in it is also large.
Thus the molecules on average, possess higher velocities. This
means that the relative velocity between any two molecules will
high. Assuming that every molecule is radiating for the spectral
line, due to the relative motion, the frequency of the signal
received will be Doppler shifted by an amount which is
characteristic of its velocity.
This range of frequencies due to the Doppler Shift will therefore broaden the Spectral Line. A broader spectral line thus indicates a hotter star.