In the Noah’s Ark story, a rainbow marked God’s covenant after the flood.
Genesis 9 describes a covenant between God and Noah, his descendants, and every living creature after the waters recede. God places a rainbow in the cloud as the sign of that covenant and associates it with the promise never again to destroy all flesh by a flood.
The rainbow is sometimes confused with the dove and its olive leaf. Those belong to the earlier part of the story: Noah sends birds to determine whether the waters have gone down, and the dove returns with a freshly plucked olive leaf.
Genesis presents the rainbow as a covenant sign, not as a method Noah used to navigate or measure the flood. The passage also connects the sign with clouds and rain, giving the symbol a place in the story’s post-flood conclusion.