Green Flash?

Question

May someone please thoroughly describe this phenomenon, its for my research project in school. If you know anything about it, tell me everything you know.

~ThankYou~

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Answer 1

What are you talking about?

What green flash?

Answer 2

This is a rather complicated phenonemon, and hard to describe.

First, we have to go back a step, to describe why the sky seems blue:

The sky seems blue, because the blue part of the spectrum is scattered by the molecules in the atmosphere.  What this means is that the blue part of the spectrum of sunlight is absorbed by the molecules in the air; then re-emitted.  The re-emitted blue light may then be absorbed by other molecules and re-emitted, and so on.  Because the blue light is re-emitted in all directions, and gets 'bounced around' in this way before it reaches us; the blue light seems to be coming from everywhere; so the sky seems blue.

This effect is called 'Rayleigh scattering'; and the shorter the wavelength, the more the light is scattered.  The longest wavelengths of visible light; the yellow and red, tend to pass straight through.  The wavelengths shorter than blue (indigo and violet) get scattered even more; but our eyes are not as sensitive to violet as they are to blue; and there is less violet than blue light in the spectrum.  But the blue of the sky can sometimes take on a violet tinge.

Late in the afternoon (or early in the morning), the sun's rays come towards us at a much lower angle.  The blue light has been scattered away, and we see more of the red and yellow; hence the colours of the setting sun.

Now recall the colours of the spectrum:

Red, orange, yellow, green, blue, indigo, violet.

We have discussed the blue, indigo and violet, red orange and yellow.  But what about the green?

This is the genesis of the green flash.

In some circumstances; moments after the sun sets, the blue has already been scattered away.  At that moment, the red is blocked from view, and the yellow and orange have been absorbed in the atmosphere.

That leaves only one colour: green.

For a fleeting moment, a vivid green ray can be seen.  This is the green flash.

The green flash is very difficult to see; you need an unobstructed view of the horizon in clear air, and it is a fleeting phenonemon:  Except in two cases: at high altitude (Astronauts and baloonists see them frequently) and at high latitude. (Near midnight sun, when the sun is just below the horizon, the green fash can last several minutes).

There is a beautiful description of the green flash in the book "The Earth's Aura" by Louise Young.