Gen. 1:17   And God, (i.e.; Reality), set: [nathan: appointed, assigned, designated] them in the firmament of the heaven to give light upon the earth (in circadian rhythm).

Gen. 1:18   And to rule over the (cycle of the @12 hours) day and over the (cycle of the @12 hours) night, and to divide the light from the darkness: and God, (i.e.; Reality), saw that it was good.