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Astrodynamic Constants

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+ Center for Near-Earth Object Studies  Constants  Defining Primary Derived 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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