Question

the image above shows the doppler - shifted absorption spectra of three stars, compared to the stationary lab spectra.
a) which star(s) is/are moving towards us?
b) which star(s) is/are moving away from us?
c) which star is moving the fastest?
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Explanation:

Step1: Understand Doppler - shift principle

In astronomy, a blue - shift indicates an object is moving towards the observer and a red - shift indicates an object is moving away from the observer. The greater the shift, the faster the speed.

Step2: Analyze star spectra for motion direction

Compare the star spectra with the lab spectra. Star B has its spectral lines shifted towards the blue end compared to the lab spectra, so it is moving towards us. Stars A and C have their spectral lines shifted towards the red end, so they are moving away from us.

Step3: Determine the fastest - moving star

The star with the greatest amount of red or blue - shift is the fastest - moving. Star C has the largest red - shift among the three stars, so it is moving the fastest.

Answer:

a) Star B
b) Star A, Star C
c) Star C