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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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