Pirate movies turned the green flash into a sign of a soul returning from the dead, but the burst of green light at the last sliver of sunset is a real and surprisingly complex physics demonstration. This episode explains how Earth's atmosphere acts as a giant prism at sunset, bending red light the least and blue light the most, so that by the time you see the sun touching the horizon the physical star has already set. It then covers Rayleigh scattering, which knocks the blue light out of the race through the thick horizontal slice of atmosphere and leaves green as the last color to reach your eye.

The conversation explains why a microscopic green rim exists at almost every clear sunset yet is nearly impossible to see without a mirage created by stacked layers of warm and cold air, why airline pilots flying west are among the most frequent  ...