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Jim Mosher
sage
Reged: 05/22/06
Posts: 233
Loc: Newport Beach, CA
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Re: Lunar X - August illumination (Werner X)
08/09/08 12:39 PM
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Phil,
According to the information collected on the-Moon Wiki, the appearance of the X is controlled by the Sun's altitude over a point on the Moon's surface at about 0.9° east longitude and 25.2° south latitude. Various observers have reported seeing a "perfect" X when the Sun's altitude above the horizon (at that point on the Moon) is anywhere from about -2° to 0°. At the time of your photo, the Sun was at an altitude of -0.06°, which I guess the more expert observers would regard as near where the X starts to merge with its surroundings. You can see examples of what the X looks like at several sun angles on the Wiki page and elsewhere.
I don't know the exact source of Dana's predictions, but there is a quite suitable Moon Event Predictor in the freeware LTVT software. Simply go to the "Sun Altitude" mode, enter 0.9 for the target longitude, -25.2 for the target latitude and -1 for the target sun angle, or better ask the software to calculate the altitude (-0.06) and azimuth (89.96) of the Sun at the time of you observation. "Filter" the output, if you wish, to suppress the events with the opposite solar azimuth (that is, sunset, rather than sunrise, events).
The next repetition of the -0.06° lighting shown in your photo (it is visible somewhere on Earth every month) will be on September 7 at 11:51 UT. Weather permitting, the next repetition visible from Long Island, NY will be on October 6 at 23:37 UT, with the Moon 20° above your horizon (very slightly better than last night). An hour earlier that evening, at sunset, you should be able to see the Lunar X illuminated at the slightly more "perfect" sun angle of -0.6°. Dana seems to be giving the times when the sun angle is a still more perfect -1.0° (which, in October, as it did this month, will occur before sunset from your location).
-- Jim
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