In the Lyot micrometer the displacement d of the ordinary image with respect to the extraordinary image given in arcseconds is:
where e = thickness of the calcite F = effective focal length of the telescope i = angle of incident ray ne = refractive index of extraordinary ray = 1.48639 (T = 18 °C)
no = refractive index of ordinary ray = 1.65836 (T = 18 °C)
The refractive indices vary with temperature and wavelength. The dependency on the temperature T is:
Ane (T) = 1.18 x 10-5 per °C Ano (T) = 2.1 x 106 per °C
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