What does a rainbow mean?

It means nothing, it's only a natural phenomenon: A rainbow is caused by sunlight and atmospheric conditions. Light enters a water droplet, slowing down and bending as it goes from air to denser water. The light reflects off the inside of the droplet, separating into its component wavelengths--or colors. When light exits the droplet, it makes a rainbow ¯\_(ツ)_/¯

It is the sign of the Noahide covenant. Before the Flood the rainbow was an uncomon occurance but then God made it that the light would cause a special incidence or refraction of the water droplets causing the giant rainbow in the sky. Why is it you only see 1 rainbow in the sky? It's because it serves as an ot-sign. You will also find that no matter what hour of the day even at sunset the rainbow will appear high in the sky! Very rarely a water droplet can be refracted 3 or 4 times! Usually however only at 45 degrees will you see a rainbow although technically other angles are also possible to produce a rainbow.

If you already know the Biblical answer, why ask the question.

That is not what a rainbow means, but I am sure many people take comfort in the scripture.

Well I guess you have answered your own question - so I don't need to

The causes of such natural events are fully understood by science, and they are not supernatural.

It means that the destruction of the world will be by another way, 2 Pet. 3:10.

Yes, rainbows are formed by water droplets in the air being hit by rays of light that become refracted into the color spectrum we see around us. I think the reason rainbows were not seen before the flood had something to do with the amount of water droplets in the air; until the Flood, a large collection of these droplets in an airborne fashion was rare. Since the Flood, God decided that the rainbow would be his sign of peace, saying that he will not destroy the earth in a flood of water ever again. Why the LGBTQ decided to claim the rainbow to mean a spectrum of genders is beyond me.

God is upset with Al gore saying the world going to flood again also a promise that it will be like the days of noah when Jesus Christ returns newton doesn't change that

It means that the angle of refraction of light is dependent on the frequency.

It means that there is enough water in the air to cause sunlight to refract.