Ibn Ezra

And He made - the two were called "great" as compared to the stars. Similarly, the three [oldest] sons of Yishai were called "great/oldest" as compared to the others, while Eliav was the first-born, the oldest of all of them. It does not mean [here] that one was greater than the other, for there is a hidden meaning - the dominion of the sun in the day and not at night, for it has no light [then]. And likewise regarding the moon and starts, their light is not seen in the day. Now if one should ask, behold the astronomers have said that Jupiter and all the planets except for Mercury and Venus are larger than the moon, so how can it write "the great ones" [including the moon]? The answer is that "the great ones" does not refer to their physical measure, but rather to their light, and the light of the moon is many times greater, due to its being close to the earth, and therefore is it written "luminary".