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Astronomical refraction |
 | | “Astronomical refraction” is the angular displacement of astronomical objects from their true or geometrical position, because of the bending of rays in the Earth's atmosphere. |
 | | While terrestrial refraction is often imperceptible to the naked eye, it's huge compared to the errors of measurement in surveying, which are a few seconds of arc, or less. |
 | | For this reason, all the refraction phenomena near the horizon — mirages, dip, terrestrial refraction, etc., as well as the astronomical refraction — are very sensitive to the temperature gradient; and they all vary a great deal more than does the astronomical refraction well up in the sky. |
| mintaka.sdsu.edu /GF/explain/atmos_refr/astr_refr.html (884 words) |
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