Genesis 9:13-15 the rainbow is a sign that no more will floods come to destroy all life.
There is nothing to this " covenant " but silly myth and superstition.
A quick Google will explain the mechanisms of rainbows and any third rate poet can expound on the wonder of rainbows.
Other people asked questions on similar topics, check out the answers they received:
Other people asked questions on various topics, and are still waiting for answer. Would be great if you can take a sec and answer them