Saw this rainbow appearing above AJC last night on the way to dinner..
Of course we do know the scientific explaination of rainbows:

Rainbows can be observed whenever there are water drops in the air and sunlight shining from behind a person at a low altitude angle (on the ground). The most spectacular rainbow displays happen when half of the sky is still dark with draining clouds and the observer is at a spot with clear sky in the direction of the Sun. The result is a luminous rainbow that contrasts with the darkened background.The rainbow effect is also commonly seen near waterfalls or fountains. The effect can also be artificially created by dispersing water droplets into the air during a sunny day

The light is first refracted as it enters the surface of the raindrop, reflected off the back of the drop, and again refracted as it leaves the drop. The overall effect is that the incoming light is reflected back over a wide range of angles, with the most intense light at an angle of 40°–42°. The angle is independent of the size of the drop, but does depend on its refractive index. Seawater has a higher refractive index than rain water, so the radius of a 'rainbow' in sea spray is smaller than a true rainbow. This is visible to the naked eye by a misalignment of these bows.^[2]

The amount by which light is refracted depends upon its wavelength, and hence its colour. Blue light (shorter wavelength) is refracted at a greater angle than red light, but due to the reflection of light rays from the back of the droplet, the blue light emerges from the droplet at a smaller angle to the original incident white light ray than the red light. You may then think it is strange that the pattern of colours in a rainbow has red on the outside of the arc and blue on the inside. However, when we examine this issue more closely, we realise that if the red light from one droplet is seen by an observer, then the blue light from that droplet will not be seen because it must be on a different path from the red light: a path which is not incident with the observers eyes. The blue light seen in this rainbow will therefore come from a different droplet, which must be be below that whose red light can be observed.

Contrary to popular belief, the light at the back of the raindrop does not undergo total internal reflection and some light does emerge from the back. However, light coming out the back of the raindrop does not create a rainbow between the observer and the sun because spectra emitted from the back of the raindrop do not have a maximum of intensity, as the other visible rainbows do, and thus the colours blend together rather than forming a rainbow.

But do we know what the Bible has to say about Rainbows?

When God appeared unto Noah after the flood, and placed a rainbow in the sky; he did much more than show him a phenomenon. In the seven colours of the rainbow, beginning with red and ending with purple, God was displaying a natural miracle that demonstrated the complete redemption and salvation of man.

First let us look at colour in the natural world. In the world of art, we have three primaries; red, yellow and blue. These cannot be formulated by mixing. They come from the earth; but with these three colours, and the addition of black and white, any shade of the spectrum can be obtained.

In this fact alone lies a thought provoking, scriptural principle!

White is the colour that is comprised of all the colours of the spectrum. Refraction of white light produces the rainbow colours which consist of red, orange, yellow, green, blue, indigo (purple), violet. Other colours consist of the infrared and Ultraviolet spectrum Infrared and Ultraviolet represent that which is unseen.

The rainbow represents the promises of God and was a sign of the covenant that God would never again flood the earth with water: "I have set my bow in the clouds, and it shall be a sign of the covenant between me and the earth. When I bring clouds over the earth and the bow is seen in the clouds, I will remember my covenant that is between me and you and every living creature of all flesh; and the waters shall never again become a flood to destroy all flesh." Gen 9:13,15

The rainbow signifies the glory, majesty and honour of the Lord Jesus Christ "One sat on the throne. And He who sat there was like a jasper and a sardius stone in appearance; and there was a rainbow around the throne, in appearance like an emerald." (Rev 4:2-3)