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Re: Night moon sights
From: Trevor Kenchington
Date: 2004 Feb 1, 08:37 +0000
From: Trevor Kenchington
Date: 2004 Feb 1, 08:37 +0000
Peter Fogg wrote: > All agree that there is a false horizon line, where the moon's > relected light is cut off, some way between the real horizon and the > point of observation. Provided that the Moon's altitude is high enough. For any given sea state and height of eye, there must be some altitude below which rays of light from the Moon strike the observer's horizon and there reflect to his eye. Presumably, it is when the Moon is below that altitude that the irradiation effect becomes important and the false horizon rises above the real horizon. At a guess, small boats and high latitudes tend to make for reflected light reaching to the true horizon and hence a raised false horizon while large heights of eye and low latitudes tend to give the reverse -- though I have never attempted a sextant sight under either set of conditions, so this is purely theoretical for my part. Trevor -- Trevor J. Kenchington PhD Gadus@iStar.ca Gadus Associates, Office(902) 889-9250 R.R.#1, Musquodoboit Harbour, Fax (902) 889-9251 Nova Scotia B0J 2L0, CANADA Home (902) 889-3555 Science Serving the Fisheries http://home.istar.ca/~gadus