Charles Ellicott Commentary Psalms 104:19

"He appointed the moon for seasons: The sun knoweth his going down." — Psalms 104:19 (ASV)

The moon for seasons.—See Psalm 89:37, Note. The mention of the lesser luminary first is undoubtedly partly due to its importance in fixing the calendar, but partly also to the daily reckoning, the evening and the morning, as making the day.

The sun knoweth.—So Job 38:12, concerning the dawn. The sun is no mere mechanical timepiece to the Israelite poet, but a conscious servant of God. How beautifully this mention of sunset prepares the way for the exquisite picture of the nocturnal landscape, as the sunrise in Psalm 104:22 does for the landscape of the day.

In Genesis, the creation of the “heavenly bodies”—the fourth day’s work—is related, so to speak, in a scientific manner. But the poet, as in the former part of his treatment of the subject, immediately considers the influence of these phenomena on living beings.

In Genesis, the lamps of heaven are, as it were, set in place at God’s command. In the poem, however, they seem to move to their office of guiding the seasons and illuminating the earth like living things that are conscious of the glorious function they have to perform.