In the Genesis account of Noah's Ark, God set a rainbow in the clouds as the sign of the covenant.
After Noah left the Ark, Genesis describes God making a covenant with Noah, his descendants, and every living creature. The covenant promised that a Flood would not again destroy all life on earth. The rainbow served as the visible reminder of that promise.
This passage is one reason the rainbow is strongly associated with the Flood story. The text presents it as a sign placed in the clouds, not merely as a natural phenomenon noticed by Noah. Genesis also connects the covenant with the preservation of the earth’s regular cycles of seasons, day and night, planting, and harvest.