Table of Astronomical Constants
| Quantity | Symbol | Value | Relative uncertainty |
Ref. |
|---|---|---|---|---|
| Defining constants | ||||
| Gaussian gravitational constant | k | 0.017 202 098 95 A3/2 S−1/2 D−1 | defined | |
| Speed of light | c | 299 792 458 m s−1 | defined | |
| Mean ratio of the TT second to the TCG second | 1 − LG | 1 − 6.969 290 134×10−10 | defined | |
| Mean ratio of the TCB second to the TDB second | 1 − LB | 1 − 1.550 519 767 72×10−8 | defined | |
| Primary constants | ||||
| Mean ratio of the TCB second to the TCG second | 1 − LC | 1 − 1.480 826 867 41×10−8 | 1.4×10−9 | |
| Light-time for unit distance | τA | 499.004 786 3852 s | 4.0×10−11 | |
| Equatorial radius for Earth | ae | 6.378 1366×106 m | 1.6×10−8 | |
| Potential of the geoid | W0 | 6.263 685 60×107 m2 s−2 | 8.0×10−9 | |
| Dynamical form-factor for Earth | J2 | 0.001 082 6359 | 9.2×10−8 | |
| Flattening factor for Earth | 1/ƒ | 0.003 352 8197 = 1/298.256 42 |
3.4×10−8 | |
| Geocentric gravitational constant | GE | 3.986 004 391×1014 m3 s−2 | 2.0×10−9 | |
| Constant of gravitation | G | 6.674 28×10−11 m3 kg−1 s−2 | 1.0×10−4 | |
| Ratio of mass of Moon to mass of Earth | μ | 0.012 300 0383 = 1/81.300 56 |
4.0×10−8 | |
| General precession in longitude, per Julian century, at standard epoch 2000 | ρ | 5029.796 195″ | * | |
| Obliquity of the ecliptic, at standard epoch 2000 | ε | 23° 26′ 21.406″ | * | |
| Derived constants | ||||
| Constant of nutation, at standard epoch 2000 | N | 9.205 2331″ | * | |
| Unit distance = cτA | A | 149 597 870 691 m | 4.0×10−11 | |
| Solar parallax = arcsin(ae/A) | π☉ | 8.794 1433″ | 1.6×10−8 | † |
| Constant of aberration, at standard epoch 2000 | κ | 20.495 52″ | ||
| Heliocentric gravitational constant = A3k2/D2 | GS | 1.327 2440×1020 m3 s−2 | 3.8×10−10 | |
| Ratio of mass of Sun to mass of Earth = (GS)/(GE) | S/E | 332 946.050 895 | ||
| Ratio of mass of Sun to mass of (Earth + Moon) | (S/E) (1 + μ) |
328 900.561 400 | ||
| Mass of Sun = (GS)/G | S | 1.9818×1030 kg | 1.0×10−4 | † |
| System of planetary masses: Ratios of mass of Sun to mass of planet | ||||
| Mercury | 6 023 600 | |||
| Venus | 408 523.71 | |||
| Earth + Moon | 328 900.561 400 | |||
| Mars | 3 098 708 | |||
| Jupiter | 1047.3486 | |||
| Saturn | 3497.898 | |||
| Uranus | 22 902.98 | |||
| Neptune | 19 412.24 | |||
| Pluto | 135 200 000 | |||
| Other constants (outside the formal IAU System) | ||||
| Parsec = A/tan(1") | pc | 3.085 677 581 28×1016 m | 4.0×10−11 | † |
| Light-year = 365.25cD | ly | 9.460 730 472 5808×1015 m | defined | † |
| Hubble constant | H0 | 70.1 km s−1 Mpc−1 | 0.019 | |
| Solar luminosity | L☉ | 3.939×1026 W = 2.107×10−15 S D−1 |
variable, ±0.1% |
|
- Notes
* The theories of precession and nutation have advanced since 1976, and these also affect the definition of the ecliptic. The values here are appropriate for the older theories, but additional constants are required for current models.
† The definitions of these derived constants have been taken from the references cited, but the values have been recalculated to take account of the more precise values of the primary constants cited in the table.
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