Dear Tom,

I recently discovered that it is possible to witness the green flash at sunrise as well as at sunset.  Just curious, has there ever been a sighting near Chicago?
Tom Mulloy

Dear Tom,

The “green flash” is a very brief flash of green light that emanates from the upper rim of the rising or setting sun. Sunlight is bent slightly upward in its passage through the atmosphere, and the bending is greatest when the sun is on the horizon. Because the shortest wavelength constituents of sunlight, blue and green, are bent upward the most, those colors are the first to appear on the upper rim of the rising sun and the last to appear as the sun sets. The atmosphere scatters most of the blue, leaving green as the shortest wavelength to make it through. Sometimes the atmosphere’s temperature structure causes it to act like a magnifying glass, enlarging the green rim to create a brief green flash. Though rare, the green flash has undoubtedly been seen over Lake Michigan; at sunrise on the Chicago side and sunset on the Michigan and Indiana shores.

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