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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: U.S. Standard Atmosphere Supplements
From: Frank Reed CT
Date: 2005 Aug 27, 02:05 EDT
From: Frank Reed CT
Date: 2005 Aug 27, 02:05 EDT
Fred you wrote: "Frank (or should I say, Frank I :)" Soon we will be forced to invent the "surname". ;-) You wrote: "That's very nice evidence for the anomalous dip that George Huxtable is so fond of mentioning, wouldn't you say? The most convincing demonstration I have seen at least. I wonder how far below "ref" the refraction at 0 degrees altitude would go. Seven minutes above is astounding." The variability of refraction right at the horizon is distinct from anomalous dip, since the light ray from an astronomical source traverses the whole atmosphere, grazes ground level, and then travels the last few miles to the observer's eye. The light ray from the horizon itself only does the last part of the trip. It could be calculated in more or less the same way though. So if a single day's difference in atmospheric conditions at a site chosen at random can yield a six arcminute difference in refraction right at the horizon and one arcminute at half a degree altitude, why don't we notice it? I think the simple answer is that we never measure any astronomical objects down that low except the Sun and the Moon and them very rarely. The variability in refraction will change the exact time of sunrise/set and moonrise/set by something like a half a minute (depending on latitude) for a six arcminute change in refraction. I think the time of sunset is as variable as that on a regular basis. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars