Question

why do scientists observe blueshift in certain stars? (1 point)
stars with higher temperatures emit more light waves at the blue end of the spectrum.
stars with lower temperatures emit more light waves at the blue end of the spectrum.
light wave frequencies decrease as an object moves toward the observer.
light wave frequencies increase as an object moves toward the observer.

Explanation:

Blueshift is related to the Doppler effect for light. When an object (like a star) moves toward an observer, the light waves are compressed, leading to an increase in frequency (and a shift toward the blue end of the spectrum, since blue light has higher frequency than red). The first two options are incorrect because blueshift is not about a star's temperature emitting more blue - spectrum light, but about motion. The third option is wrong as moving toward the observer increases, not decreases, light wave frequencies.

Answer:

D. Light wave frequencies increase as an object moves toward the observer.