Symbolism, Imagery, Allegory
The Assyrians and Babylonians were big believers in astrology. For the Minor Prophets, however, believing in the influence of the heavenly spheres on daily life was inconsistent with belief in Yahweh’s total control over all things. In ancient Israel, putting an astrology app on your Galaxy was a serious no-no.
So what better way to tweak the followers of other gods than by saying that the day of the Lord is a great big lights out.
The earth quakes before them, the heavens tremble. The sun and the moon are darkened, and the stars withdraw their shining. The LORD utters his voice at the head of his army; how vast is his host! Numberless are those who obey his command. Truly the day of the LORD is great; terrible indeed—who can endure it? (NRSV Joel 2:10-11)
The Babylonian constellations included an eagle, which just so happens to be found in the same constellation now known by the Latin word for eagle, Aquila. Guess who happens to show up in the book of Obadiah, which many scholars believe refers to Edom joining with Babylon to gang up on Judah?
Though you soar aloft like the eagle, though your nest is set among the stars, from there I will bring you down, says the LORD. (NRSV Obadiah 1:4)
A God who creates and controls the celestial bodies is a way of sticking it to the nations who believe that the moon and sun are themselves things to be worshipped.