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Re: Refraction
From: Frank Reed CT
Date: 2005 Aug 16, 14:17 EDT

Marcel you wrote: "Probably one should calculate refractive index for the dominant wavelength depending on the object's zenith distance?" Depends on your goal. If you're trying to portray the appearance of stars at very low altitudes in the atmosphere, then you should calculate refraction for each color of the spectrum (split up as you choose). When you see stars very low in the sky, they do, in fact, look like little "French flags" because the red light is refracted more than the blue light. For navigational purposes, this is irrelevant, but for the project you briefly described earlier it might be interesting to include. But be sure to include extinction. NO stars are visible to the unaided eye right at the horizon since the extinction is on the order of twelve magnitudes. Fortunately, if you do a proper numerical integration for refraction, you get the extinction "for free". -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars

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