What is the formal term for the speed measured along a star's line of sight?
Answer
Radial velocity
Radial velocity is the component of a star's motion directed precisely along the line connecting the star and the observer. This velocity is directly proportional to the degree of the spectral shift (redshift or blueshift) observed. It represents only the portion of the star's total movement that involves approaching or receding, and it is determined instantaneously by analyzing the displacement of the spectral lines against their known reference positions.
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