Pulkovo astronomical refraction

Function returns astronomical standard refraction as function of apparent zenith distance. Digitized from Abalakin, V. (1985).

Digitized, corrected and smoothed (rounding) Pulkovo tables* for astronomical refraction, endorsed by the IAU as standard reference. Reproduces the table values to better than 1 unit in the last digit (+/-5e-6 in log(r0/arcsec) or 1.15e-5*r0 in absolute values), mostly significantly better due to smoothing the rounding steps. Result can be given to 0.001 .. 0.01 arcsec.

The processed table values are read in from a mat file and interpolated (spline). Slight extrapolation beyond z=90° is possible.

Returns r0 in arcsec with z, the apparent zenith distance, in deg. 0<=z<=90°.

*Abalakin, V. (1985). Fifth edition is the latest edition. It gives log10(r0) every 1 arcmin from 0°0' to 90°0' apparent zenith distance. For other conditions, the values need to be corrected. Planned for a later version of this function.

Result refers to standard conditions: 1013.25 mbar atmospheric pressure, +15°C air temperature, water vapour pressure 0 mbar (dry air), wavelength 590 nm, 45° geographical latitude, 0 m height above sea level. Typos corrected! Especially at z=90° corrected to 1976.28" instead of 1977.97", 1.69" smaller! (not at 89° 59'!). This is consistent to Lovchy, I. (2021). See also Kurzyńska, K. (1988).