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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Refraction
From: Frank Reed CT
Date: 2005 Aug 16, 14:09 EDT
From: Frank Reed CT
Date: 2005 Aug 16, 14:09 EDT
Marcel, you wrote: "Index with "dry part" only =1.000277 -> Refraction = 30.27 minutes Index with "dry part" and "wet part" =1.000293 -> Refraction = 32.17" I don't think the effect of humidity is this large. Going from one end of the humidity scale to the other (20% to 85%) changes the refractivity by only about 0.2% so that the change in refraction even at the horizon is less than 0.1 minutes of arc. By comparison, a 1 degree Celsius change in temperature yields 0.3% change in the refraction. Accurate knowledge of the exact temperature is far more important than the humidity. And: "At this point it really would be interesting to know to what values Bennett fitted the approxiation formula." That's easy. They're the values in the tables in the front of the Nautical Almanac --which have been the same for decades (apart from an absurdly trivial and pointless modification in 2004). -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars