Episode Details

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 observers, and why looking at the sun through binoculars or a telescope is dangerous. It then explores extreme cases: the hourglass-shaped subduct flash lasting up to 15 seconds, the 35-minute green rim recorded by Richard Byrd's 1930s Antarctic expedition where explorers climbed antenna posts to stay in the beam, the rare blue flash, and the first color photograph taken from the Vatican Observatory in 1960. It closes with the cultural life of the phenomenon, from Jules Verne to Pirates of the Caribbean and Pokemon.

• Why sunlight at the horizon travels through far more air than at noon
• How the atmosphere projects the sun higher than its true position
• The highway-and-train analogy for how pilots slow down the sunset
• Why polar geometry and cold inversions produced a 35-minute green flash
• Why humans attach transcendent meaning to a trick of air density