When an astronomical source is moving toward an observer, what spectral shift is observed?
Answer
Blueshift
The movement of a celestial object relative to an observer dictates how its emitted light waves are perceived, according to the principles of the Doppler effect. If a star or galaxy is moving toward the observer, the distance between successive wave crests in the light decreases as the light travels across space. This compression shortens the observed wavelength of the light. This shortening shifts the characteristic spectral lines toward the higher frequency, shorter wavelength region of the spectrum, which visually corresponds to the color blue. Therefore, approach is marked by a blueshift, serving as the direct opposite indicator to the redshift observed for receding objects.
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