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Astrodynamic Constants

This page contains selected constants commonly used in astrodynamic computations. The term "constant" is used loosely. Specifically, some values are derived from other constants and/or results of numerical fits to measured data (e.g. planetary mass ratios). Constants are represented in three groups: "defining", "primary", and "derived". References are listed below.

Defining Constants

 Julian day    d = 86400 s 
 Julian year    y = 365.25 d 
 Julian century    Cy = 36525 d 
 speed of light    c = 299792458 m/s 
 astronomical unit    au = 149597870700 m 

Primary Constants

 mean sidereal day    86164.09054 s [ 23:56:04.09054 ] 
 sidereal year (quasar ref. frame)    365.25636 d 
 gravitational constant    G = 6.67259 (± 0.00030) x 10-11 kg-1 m3 s-2  
 general precession in longitude    5028.83 (± 0.04) arcsec/Cy 
 obliquity of ecliptic (J2000)    epsilon = 84381.412 (± 0.005) arcsec 
 obliquity of ecliptic (J2000) [IAU 1976]    84381.448 arcsec 
 mass ratio: sun/Mercury    6023600. (± 250.) 
 mass ratio: sun/Venus    408523.71 (± 0.06) 
 mass ratio: sun/(Earth+Moon)    328900.56 (± 0.02) 
 mass ratio: sun/(Mars system)    3098708. (± 9.) 
 mass ratio: sun/(Jupiter system)    1047.3486 (± 0.0008) 
 mass ratio: sun/(Saturn system)    3497.898 (± 0.018) 
 mass ratio: sun/(Uranus system)    22902.98 (± 0.03) 
 mass ratio: sun/(Neptune system)    19412.24 (± 0.04) 
 mass ratio: sun/(Pluto system)    1.35 (± 0.07) x 108  

Derived Constants

 light time for 1 au    tauA = au/c = 499.004783836 s 
 heliocentric gravitational constant    GMsun  =   1.32712440018 x 1020 (± 8 x 109) m3 s-2  
 mass ratio: Earth / Moon      81.30059 (± 0.00001) 

Notes and References

  • Data are from the 1994 IAU file of current best estimates unless otherwise noted.
  • Planetary ranging determines the Earth/Moon mass ratio.
  • The value for 1 au is from the IAU 2012 Resolution B1.
  • JPL asteroid and comet ecliptic orbital elements are based on the adopted IAU 1976 constant for the obliquity of the ecliptic.

Standish, E.M. (1995) "Report of the IAU WGAS Sub-Group on Numerical Standards", in Highlights of Astronomy (I. Appenzeller, ed.), Table 1, Kluwer Academic Publishers, Dordrecht.

Standish, E.M. (1998) "JPL Planetary and Lunar Ephemerides, DE405/LE405", JPL IOM 312.F-98-048.

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