Redshift is observed when:
a. a distant luminous object travels rapidly away from an observer
b. a luminous object travels rapidly towards an observe
c. a luminous object is stationary
relative to an observe
d. a luminous object traveling alongside an observe
a. a distant luminous object travels rapidly away from an observer
To determine the correct answer to this question, we need to understand what redshift is and what causes it. Redshift refers to the elongation of light waves towards longer wavelengths, which shifts the light spectrum towards the red end.
One essential concept in understanding redshift is the Doppler effect. The Doppler effect explains how the wavelengths of waves (including light) change relative to an observer when there is motion between the source of the waves and the observer. When an object emitting light is moving away from an observer, the wavelength of the light waves gets stretched, leading to redshift. Conversely, when an object emitting light is moving toward an observer, the wavelength of the light waves gets compressed, causing blueshift.
Based on this information, we can determine that the correct answer is (a) a distant luminous object traveling rapidly away from an observer. As the object moves away, the light waves emitted by the object stretch, resulting in a shift towards the red end of the spectrum (redshift).