> > Of course you were :-) The only point you might want to expand on is that when the sun is nearest the horizon, the rays are traveling tangent to the viewer and, hence, through a larger distance of air. The further the sunlight has to travel through air molecules, the more likely the shorter-wave component of light (blue) is scattered out -- allowing only warmer red, orange, and yellow light to reach and delight the viewer's eyes.
>
> Now explain why the sky never appears green, even around the outer edge of a sunrise/sunset or just as it's appearing or disappearing.


You know, Sam's asking an interesting question there... Why *shouldn't* the sky appear green?
So after some rummaging in some geo- and meteological notes we have, and much to my surprise, I finally found a description of the "green flash" phenomena by someone called Jack. He writes:

"The green flash is very much real; photos have been taken of it. The green flash is a relatively rare optical effect that usually occurs just above the disk of the setting sun, right at sunrise and sunset, usually when the sky is clear. The optical effect that causes the more common orange and red sunset, also helps causes the green flash. As the sun begins to set various things are happening:

• First, the atmosphere is bending the light from the sun. This bending of light means that when we see the very top of the sun disappear below the horizon, the sun is really already below the horizon, we're seeing light rays bent by the atmosphere.
• This atmospheric refraction bends blue light the most - different wave lengths bend by different amounts. This would seem to mean the last thing we see should be a blue flash.
• But, the atmosphere scatters blue light the most. This is why the sky is blue and sunsets tend to be red and yellow. With light having to travel through more of the atmosphere when the sun is low in the sky, much of the blue light is scattered away and we see the red and yellow.
• The resulting "compromise," says Robert Greenler in his book "Rainbows, Halos, & Glories" (Cambridge Press, 1991) is a flash of green light.

The best chance of seeing a green flash is when you're watching the sun set over a low horizon, such as over a ocean or large lake. Looking for the green flash is a good excuse to end your day relaxing with a drink watching the sun set." (7-1-96)


Wolf "Now who wants to explain 'Why is the grass green'?" spirit