A skater experiences the same thing, when suddenly a skate hits a rough spot and that skate slows. The skater turns toward the slower skate.

Light bends in a similar way both when it enters and leaves the raindrop.  See Figure 2.

Figure 2.  Light enters a raindrop (the circle), bends different amounts, and displays colors (red and violet illustrated).  Sketch from Beverly T. Lynds' About Rainbows.

Some colors slow more than others and therefore bend more. Violet light, for example, travels slower than red. That separates the violet from red light.

The red light emerges at a 42-degree angle to the original white ray. The violet reappears at only 40 degrees. The raindrop has separated the white light into colors and then re-directed the colored light back towards you. That's why you see the rainbow.

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