Suppose that you\'d like to find out if a distant star is moving relative to the

Question

Suppose that you'd like to find out if a distant star is moving relative to the earth. The star is much too far away to detect any change in its brightness as it moves toward or away from the earth. Instead we can use the Doppler effect to determine its relative speed. For this problem we are going to look at the spectral lines from hydrogen, specifically the one with a wavelength of 656.46 nm.

Part A:

Suppose that you measure the light of a star between 640 and 680 nm and you get a very strong peak around 650 nm. What can you say about the star's motion? Please provide a detailed explanation.

Explanation / Answer

The wavelength of one of the Hydrogen lines = 656.46 nm.

A]

The peak wavelength observed from the light of the star = 650 nm

this is smaller than the wavelength of hydrogen line chosen - 656.46nm.

This implies that the frequency of the light will be greater here. Thus, the star is moving towards the Earth and the light coming to the earth from the star is said to be Blue-Shifted (wavelength decrease towards blue region).

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