VALUES USED FOR ASTRONOMICAL CONSTANTS BY George Gladfelter
May 13, 2020

Astronomical Unit       149597870.7 km    IAU definition of the A.U.

Radius of Sun              696000 km      see AA2020,JPL/Horizons

Radius Solar photosphere   696300 km      but see AA2020

Volumetric Solar radius    695700 km      see AA2019 and before

Solar Mass                      1.98855e30 kg

Solar Radiated Power            3.846e26 Watts

Solar Power at 1 A.U.        1367.6 Watts per sq. meter

Solar Color Temperature      5778 K

Earth equatorial radius      6378.1366 km (WGS84)

Earth flattening (1/F)        298.25642    see AA2019

Earth Polar semi-axis        6356.75186 km derived from flattening

Earth center to surface at 45 degrees geographic latitude (WGS84):

                             6367.4532 km (derived)

Earth Radius factor for including atmosphere:  1.015 (ad hoc)

Lunar Mean Radius            1734.4 km (+/- 0.1) AA2020 but not IAU

Lunar Equatorial Radius      1738.1 km NASA 2016

Lunar Polar Radius           1736.0 km

Mean sidereal days per UT1 day  1.00273781191135448

Speed of Light             299792.458 km/sec  (defines the meter)

Kilometers per mile             1.609344 (exact in decimal notation, defines the mile)

Julian Day for 2000-JAN-01 12hours TT      2451545.0

Julian Day (UTC) for inception of UTC      2441317.5
Julian Day (TT) at inception of UTC        2441317.5004882407

Julian Day (UT) for UNIX time = 0 seconds  2440587.5

AA = Astronomical Almanac, IAU = International Astronomical Union

The constants listed above are generally used in all programs and functions unless there might be a specific reason for using a variant. 

Other constants that are used only in one particular function or application are not listed here.