S. Y. van der Werf (vdwerf@kvi.nl) is with the Kernfysisch Versneller Instituut, University of Groningen, Zernikelaan 25, 9747 AA Groningen, The Netherlands.
A new and flexible ray-tracing procedure for calculating astronomical refraction is outlined and applied to the US1976 standard atmosphere. This atmosphere is generalized to allow for a free choice of the temperature and pressure at sea level, and in this form it has been named the modified US1976 (MUSA76) atmosphere. Analytical expressions and numerical procedures are presented for calculating dry-air refractions and for the water-vapor correction. Results for all apparent altitudes are presented and compared with The Star Almanac for Land Surveyors (1951), The Nautical Almanac (1958), and the Pulkovo tables (Refraction Tables of the Pulkovo Observatory, 1985). Dependences on sea-level pressure, temperature, and temperature gradient and on humidity are discussed.
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P0 = 1005 hPa, t0 = 7 °C, 80% rel. humidity, dT/dh = -0.0065 K/m, lat. = 50° and λ = 0.574 μm.
Recomputed Star Almanac values (this study and Ref. 9).
Using PWsat = (T/247.1)18.36 and AD(λ) and AW(λ) from Eqs. (22) and (23).
Using the CC2 form for PWsat. AD(λ)2 and AW(λ) from Eqs. (21) and (24).
Using the CC4 form for PWsat. AD(λ) and AW(λ) from Eqs. (21) and (24).
Pulkovo refraction tables, 5th ed., 1985 (Ref. 6).
P0 = 1005 hPa, t0 = 7 °C, 80% rel. humidity, dT/dh = -0.0065 K/m, lat. = 50° and λ = 0.574 μm.
Recomputed Star Almanac values (this study and Ref. 9).
Using PWsat = (T/247.1)18.36 and AD(λ) and AW(λ) from Eqs. (22) and (23).
Using the CC2 form for PWsat. AD(λ)2 and AW(λ) from Eqs. (21) and (24).
Using the CC4 form for PWsat. AD(λ) and AW(λ) from Eqs. (21) and (24).
Pulkovo refraction tables, 5th ed., 1985 (Ref. 6).
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