Rainbows

From time to time here in southern Colorado, we see some spectacular rainbows. Tonight in Pueblo was one example, with a nice double-bow behind the storm.

Phsically, here's what's happening..
When sunlight enters a water droplet (a rain drop, let's say), it bends (refracts) as it enters, bounces (reflects) at the far end of the drop and bends (refracts) again as it leaves.

Each color (red, orange, yellow, green, blue, indigo and violet) bends through a slightly different angle, and the projection gives us that spectacular light show in the sky.

When you see a double rainbow (as many did tonight), the light bounces (reflects) twice inside the drop..so in this case, the sequence would be to bend (refract) as the light enters the drop, to bounce (reflect) twice inside the drop, and to bend (refract) as it leaves, producing a secondary (dimmer) rainbow above the primary rainbow.

This secondary bow has the colors in reverse order from the way you'll see them in the main (primary) rainbow.