In Genesis, God set a rainbow in the sky as the sign of the covenant made after Noah’s Ark survived the Flood.
Genesis 9 describes God’s covenant with Noah, his descendants, and every living creature after the waters recede. The rainbow is presented as a visible reminder that the earth will not again be destroyed by a flood of that kind. The covenant therefore extends beyond Noah’s family to the wider living world in the biblical text.
The rainbow is not introduced as something Noah discovers on the ark. It appears after Noah leaves the vessel, builds an altar, and the post-Flood covenant is established. This sequence is why the rainbow is commonly associated with both the Flood and the promise that follows it.
The Hebrew Bible’s account uses the rainbow as a theological sign, while modern science explains rainbows through refraction, reflection, and dispersion of light in water droplets. Those scientific explanations address the optical phenomenon; Genesis addresses its symbolic meaning within the story.