The Green Flash

Watching the sunset the other day brought some violent discussion as to the existence of the elusive green flash and whether anyone has actually seen it in Cape Town.So heres the low down:

The green flash is an atmospheric refractive phenomenon where the top edge of the Sun will momentarily turn green. It is seen rarely by the naked eye, primarily because it requires specific conditions to occur, but also because it requires the observer to know what to look for. Despite the name, there is no “flash”; the event only lasts from a fraction of a second to at the longest, a few seconds. Its caused by  refraction of light (as in a prism) in the atmosphere: light moves more slowly in the lower, denser air than in the thinner air above, so sunlight rays follow paths that curve slightly, in the same direction as the curvature of the earth. Higher frequency light (green/blue) curves more than lower frequency light (red/orange), so green/blue rays from the upper limb of the setting sun remain visible after the red rays are obstructed by the curvature of the earth.

There are several types of green flashes and conditions to best see them include ocean horizons with surface water warmer than the overlying air,atmospheric inversions,clean air and can be seen anywhere and not just in the tropics or northern hemisphere.



~ by mcsavage on April 24, 2009.

2 Responses to “The Green Flash”

  1. Well that proves it…. no one has seen a green flash in Cape Town because the surface water here is never warmer than the overlying air!!!! PUNTO!!!!

  2. It may well be that nobody has seen the green flash in Cape Town( if anyone has please let me know!) but i must point out that the specific conditions dont ALL need to occur at once.There are several types of flashes and even the mythical green ray and they all occur under different circumstances.For more info go to

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