Hello
The setting sun can create a rich variety of colors -- from red
through to deep violet. Green is rarely seen, but it's there, if only
for a brief, moment.
That moment is called the "green flash," (According to Scots
legend...and I'm a Scotsman so it must be true :)...if you're ever
lucky enough to see it, you'll never again go wrong in matters of the
heart.)
The green flash usually occurs at the final glimpse of the setting
sun, and it lasts only for a second or two. To see it a clear,
unobstructed, and low horizon is best, like the ocean, or distant
hills.
As the sun sinks below the horizon several different effects come into
play to create the green flash. First, refraction of sunlight in the
atmosphere slightly separates its colors, like a prism. The red light
from the sun sets first, and the blueish colors set last.
Dave Thurlow, in his weather notebook, gives problably the easiest
understood explanation for a layman as follows:
"....our atmosphere weakly absorbs yellow light. At sunset the sun's
light has to plow through much more atmosphere than when the sun is
overhead, so the yellow light gets eaten up. And the atmosphere
scatters away blue light (which, after all, is why the sky is blue),
leaving a green image for the last instant as the sun slips below the
horizon."
To view the green flash you need a fairly rare set of viewing
conditions.
Most importantly you need a clear view of the horizon The line of
sight should be almost parallel to the horizon (ie you should be a sea
level or just above) and clear, pollution-free stable air is
preferable. Not surprisingly such conditions are most frequently found
over the oceans.
It is sometimes seen after storms due to the diffraction of light,
acting like a prism, through the water vapour in the air between the
viewer and the sun.
Dave Thurlows Weather Notebook (also has some cool pictures)
http://192.156.97.47/notebook/transcripts/1999/09/29.html
Pictures of Green Flashes
http://mintaka.sdsu.edu/GF/pictures.html
Google search strategy
://www.google.com/search?hl=en&ie=ISO-8859-1&q=%22Weather%22+%21green+flash%22 |
