I have never seen it, but it is real, and explained
When I worked on Mauna Kea I really tried to watch the sun set so I might glimpse the 'Flash'- I never saw it- usually there were clouds in the way- the flash needs specific atmospheric conditions to be seen- once driving home from Kona I realized that the clear sky was PERFECT for seeing the flash- the sun was setting so I pulled off the road and watched it slide beyond the horizon- it was beautiful, but no green flash....
Just a point of physics, but there also must be the possibility of a green flash at sunrise- the same physics applies, yet you never hear about it
