Why is the order of colours reverse in a secondary rainbow?
A. A secondary rainbow is produced by light which has reflected twice inside raindrops. The angle is the minimum angle (note not maximum as in the primary) away from the anti solar point in which this light can be scattered. It happens that the minimum angle for red is less than for blue, the opposite, of the primary and the order is reverse. Another way of looking at it is that the second reflection inside the water drop reverse the order of the light like looking at writing in a mirror makes it look backwards. Q. Can you see a rainbow at night? A. Yes, the moon is bright enough to produce a rainbow, and while rare, people do see it. We all just have to get out more at night. Since the moon is not near as bright as the sun, the rainbow produced by the moon at night is much weaker than a rainbow produced by the sun during the day. Our eyes see dim things as black and white, not in colour. So a night “moonbow” will look gray not colourful. Q. Can moonlight produce a rainbow? A. Yes it c
