Why is the hydrogen line in Rigel's spectrum shifted downward?

What causes the downward shift in the hydrogen line in Rigel's spectrum?

The Downward Shift in Rigel's Spectrum

The downward shift in the hydrogen line in Rigel's spectrum is caused by the Doppler effect. When an object is moving towards or away from an observer, the frequency of the light emitted by the object appears to change. This phenomenon is known as the Doppler effect, and it is responsible for the shift in the spectral lines of stars like Rigel.

Explanation of the Doppler Effect

The Doppler effect occurs because the motion of the source of light affects the wavelength of the light waves reaching the observer. When Rigel is moving away from us, the frequency of the hydrogen line in its spectrum appears to decrease, causing a downward shift in the spectral line.

Calculation of Rigel's Velocity

To calculate Rigel's velocity relative to us, we can use the formula derived from the relativistic Doppler effect. The velocity of Rigel, denoted as vr, can be calculated using the following equation:

vr = (f' / f) * c

Where: vr = velocity of Rigel f' = change in frequency of the hydrogen line in Rigel's spectrum f = original frequency of the hydrogen line c = speed of light By substituting the given values into the formula, we can determine Rigel's velocity relative to us.
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