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    Re: Selenelion, something new in eclipses
    From: Frank Reed
    Date: 2014 Oct 8, 10:49 -0700

    Robin you wrote:
    "The idea is not entirely new."

    Ha. Yeah, that's an understatement! :) Articles published by space.com generally exaggerate. It draws a crowd. :)

    I tried to find examples of early use of this word, selenelion. In fact, almost the only reference in the various historical archives online is a pamphlet published shortly after an eclipse in the year 1666, "Selenelion ou apparition luni-solaire en l'isle de Gorgone" by Payen. It was a time when Latin/Greek coinages were popular, but the term did not stick. A blog entry four years ago on the S&T web site seems to be among the first trying to resurrect the word. It seems that a more common English name for this was a "horizontal eclipse". The general idea has been around for quite a while... over 1900 years. The Venerable Bede wrote, around the year 725 AD, "Once, long ago, the Moon was eclipsed at sunset in a strange fashion while both heavenly bodies were visible above the earth" (source). Bede was paraphrasing Pliny's Natural History written around the year 77 AD.

    It's not clear to me that the idea of refraction as the cause of the "horizontal eclipse" was really intended in earlier centuries. You can get the same phenomenon from "dip" by climbing a high mountain on an island (or, today, by hopping on a plane). And of course, the Earth's shadow is big enough that it's possible to see the Moon fully eclipsed when the angle from Sun to Moon is a bit less than 180°. So even at sea level, and even if refraction did not exist, the "impossible" phenomenon would be possible. The real problem, in all these cases, is that the fully-eclipsed moon is quite faint and probably cannot be seen below five degrees altitude. If we settle on an almost fully-eclipsed moon, then there's something to observe.



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