But why does light bend? You can imagine a toy car going from a wood floor to carpeting. One wheel hits the carpet first and slows down before the other, causing the toy to turn. The direction of the wave changes in addition to the speed. The slower speed must also shorten its wavelength since the frequency of the wave doesn’t change.

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The bottom line is that bending is caused by the change in speed of light when it crosses a boundary. This is true everywhere, even in the vacuum of space if it’s going from space to our atmosphere.

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