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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Green Flash and Longitude
From: Bruce Stark
Date: 2006 Jan 6, 13:49 EST
From: Bruce Stark
Date: 2006 Jan 6, 13:49 EST
Frank and Doug,
No, I haven't seen the Green Flash, but if I happened to I'd probably count seconds until picking up time from the watch, so as to have the Greenwich time of the event. The flash itself would give local time, thus longitude. It would be an interesting stunt, nothing more.
Dip, refraction and semidiameter, plus 90 degrees, would give the sun's zenith distance. You could work it either as a time sight or LOP. Azimuth for the LOP could be had by adding or subtracting the amplitude from 270 degrees, maybe allowing a bit for the sun's change of azimuth between the time it was on the celestial horizon and the time of sunset.
Considering how inaccurate the method could be, due to uncertain refraction, it might do to get local time simply by interpolating the times of sunset given in the Almanac.
Unfortunately I can't recall reading anything about getting longitude from the Green Flash, but it's hard to believe it hasn't been proposed at various times, at least as a curiosity.
Bruce
No, I haven't seen the Green Flash, but if I happened to I'd probably count seconds until picking up time from the watch, so as to have the Greenwich time of the event. The flash itself would give local time, thus longitude. It would be an interesting stunt, nothing more.
Dip, refraction and semidiameter, plus 90 degrees, would give the sun's zenith distance. You could work it either as a time sight or LOP. Azimuth for the LOP could be had by adding or subtracting the amplitude from 270 degrees, maybe allowing a bit for the sun's change of azimuth between the time it was on the celestial horizon and the time of sunset.
Considering how inaccurate the method could be, due to uncertain refraction, it might do to get local time simply by interpolating the times of sunset given in the Almanac.
Unfortunately I can't recall reading anything about getting longitude from the Green Flash, but it's hard to believe it hasn't been proposed at various times, at least as a curiosity.
Bruce
