תּלמוד אויף תהילים 78:23

Resh Lakish said, There are seven, and these are them: Vilon, Rakia, Sh'chakim, Z'vul, Ma'on, Machon, Aravot. Vilon has no purpose at all except for the entering of morning the leaving of evening, and renewing every day the work of Creation, as it is said, (Isaiah 40:22) "That stretches out the heavens as a curtain, and spreads them out as a tent to dwell in." Rakia, within it are set the sun and moon, stars and constellations, as it is said, (Genesis 1:17) "And God set them in the Rakia of the heaven." Sh'chakim, within it stand the millstones and grind manna for the righteous, as it is said, (Psalms 78:23) "And he commanded the Sh'chakim above and opened the doors of heaven; and he rained down manna upon them to eat..."