Question

electromagnetic radiation is energy in the form of waves. planets, stars, and galaxies emit electromagnetic radiation. as one of these objects move through space toward and observer, the waves of electromagnetic radiation between the object and the observer move closer together. that is, the distance between the crests of the waves decreases, causing the wavelength to shorten. if that same object moved away from an observer, the waves between the object and the observer would move farther apart from each other. the distance between the crests of the waves would increase, and the wavelength would lengthen. when a star is moving toward earth very fast, the wavelength of its light shortens, causing it to appear slightly more blue than usual. if a star is moving away from earth very fast, the wavelength of its light lengthens, causing it to appear slightly more red. by measuring blue - shift and red - shift of light, astronomers can determine whether the star or galaxies are moving toward or away from earth, and how fast. based on the spectrums in the figure, rank the four galaxies in order of the speed with which they are moving away from earth, from slowest to fastest.

Explanation:

Step1: Understand redshift concept

Redshift indicates a galaxy is moving away from Earth. The greater the redshift, the faster the galaxy is moving away.

Step2: Analyze the spectra

We need to look at the position of the spectral lines relative to the "Red" end. The further the spectral - lines are shifted towards the red end, the higher the redshift.

Step3: Rank the galaxies

By observing the spectra, we can see that the redshift is least for galaxy A, then galaxy C, then galaxy B, and most for galaxy D.

Answer:

A, C, B, D