Genesis 1:3

. Light. The sun was made on the fourth day, and placed in the firmament to distinguish the seasons, &c.; but the particles of fire were created on the first day, and by their, or the earth's motion, served to discriminate day from the preceding night, or darkness, which was upon the face of the deep. (Haydock) --- Perhaps this body of light might resemble the bright cloud which accompanied the Israelites, Exodus xiv. 19, or the three first days might have a kind of imperfect sun, or be like one of our cloudy days. Nothing can be defined with certainty respecting the nature of this primeval light. (Calmet)