This was
your sky.

Green Flashes: Sun, Moon, Venus, Mercury

If you follow a sunset on a clear day against a distant horizon, you might see a green flash as the Sun disappears. This green flash happens because light rays travel a long path through the atmosphere. Shorter wavelengths refract more strongly than longer red wavelengths, separating the colors and making the last visible part of the solar disk look green. It's harder to see a green flash from the Moon, Venus, or Mercury.