What is a green flash or green...

Sometimes when the sun sets, the very last bit of light emitted is green, and at sunrise, the first bit of light is green. It is an actual phenomenon, not an illusion. It can happen when the Sun rises or sets on horizons that are clear, or unobstructed. The flash can last 1 to 2 seconds or more. It is easiest to see from a high position. The cause has to do with the refraction, scattering, and absorption of light. Solar colors are separated in refraction, into bands of yellow, red, green, and blue. These separated colors “set” or “rise” seemingly individually, in the order they appear as the Sun sets or rises. In this green flash phenomenon, the yellow may be absorbed, the blue may be “scattered” (a complicated concept we won’t go into here), and the red may have already “set” or is not visible, at a particular instant. What’s left is the green, just for an instant.