|I've never seen a parhelion, but I've seen plenty of green flashes (left) over the Pacific.|
The web tells me that green flashes are a type of "inferior" mirage, where the "inverted image is below the normal image." The desert oasis and hot-road water illusions are inferior mirages.
Superior mirages, I learn, are more complicated and usually involve "ducting", where abnormal heat flows ("ducts") cause rays of light to be trapped along the surface of the Earth, continuously guided along the surface without ever escaping to space. An observer within the duct sees a superior mirage of distant objects, that may actually be over the horizon--even on the other side of the Earth, in theory. Ducting near Catalina is shown at left.
Astrophotographer Mario Cugo has a whole page of green flashes, plus a ton of other cool telescope photos, including a beautiful solar eclipse sequence. His apocalyptic photo of a sunset over the Canary Islands is at left.
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