What is the green flash people see at sunset and what causes it?

Answer 1

The famous but seldom seen "green flash" or "emerald flash" which occurs just before the last part of the sun disappears from view at sunset is caused by the same atmospheric refraction and scattering effects which produce the red sunset.

Answer 2

The green flash only occurs in very clear weather, over a distant horizon (usually over the ocean). It can quite commonly be seen from some Pacific islands. In the arctic and antarctic it can sometimes be seen for extended periods, and is therefore more than a "flash".

The green flash occurs because with clear air and a clear horizon, the atmosphere is essentially a shell of nearly-transparent optical material. Refraction causes the Sun to seem higher above the horizon than it "really is" (where it would appear to be if there were no atmosphere). When the Sun is at the horizon, this effect is approximately equal to the diameter of the Sun. In other words, the Sun is "actually" all the way down when you first see the bottom of the Sun touch the horizon.

Like most transparent optical materials, the index of refraction of air is greater for blue light than for red. This means that the refraction effect is bigger for blue light than for green light than for red light, and the image of the Sun is therefore spread out into a short rainbow, where the blue Sun is a little bit higher than the green sun, which is a little bit higher than the red sun. This rainbow is much shorter than the apparent diameter of the Sun, so it is a small effect. The "blue" image of the Sun is almost totally absorbed by the atmosphere, leaving the "green" and "red" images. The red image sets first, a fraction of a second before the green image, resulting in the "green flash".

Answer 3

Yes, light "Bending" in the atmosphere to the green part of the spectrum. I have actually seen this once. Hawaii.

Answer 4

maybe the green things like grass,or hill,reflects the light from sun...