<h2>Right answer: Red </h2>
When we talk about the visible electromagnetic spectrum, we know it starts in <u>violet-blue</u> and ends in <u>red</u>.
Now, in this context the astronomer Edwin Powell Hubble observed several celestial bodies, and when obtaining <u>the spectra of distant galaxies</u> he observed that the spectral lines were displaced towards the red one (red shift), whereas <u>the nearby stars</u> showed a spectrum displaced to the blue one.
From there, Hubble deduced that the farther the galaxy is, the more redshifted it is in its spectrum, and noted that all galaxies are "moving away from each other with a speed that increases with distance".
In other words: In the past the distance between two galaxies was smaller than at present, being this <u>the proof that the universe is expanding </u>(like a balloon expands when it is filled with air).
It should be noted that the redshift is not produced by the relative movement of the galaxies with each other.
<h2>
This effect is due to the own expansion of the space among the galaxies.
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