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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.

2016-Feb-14 14:42 UT
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