What is the optical principles behind the spectacular formation of rainbow?

Answer 1

Our eyes only see light perpendicular to our eyes (If in space you can't see a stars light until you look at it) Colors bend differently due to different wavelengths. If you have ever noticed, a rainbow is opposite from the side of the sun. Raindrops work kind of like the little balls on stop signs do, by reflecting the light back at us. Because the colors bend differently we see a spectrum reflected from the sun through raindrops to our eyes.

Answer 2

Refraction of light same, principle as a prism.