Green flash is an optical phenomena that is a short (less than a second) burst of visible green light that is visible the moment after sunset or before sunrise.

A green spot becomes visible above the sun or it may resemble a green ray shooting up from the sunset on a clear, calm day when the air is warmer than the water. It occurs every sunrise and sunset, but it must be combined with an inferior mirage to be seen by the naked eye. It occurs because the sun’s rays that bend the most as they near the horizon are the blue green rays as the other colors disappear beyond the horizon.

But as open water swimmers know when they swim in the ocean, the mind can play tricks and swimmers think they see all kinds of objects (e.g., from wave sharks to finishes that remain off in the distance for long periods of time).

Copyright © 2012 by World Open Water Swimming Association