Section: 14 | Astronomical Constants |
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One or more tables in this document differ to those in the book. This is due to space restrictions in the book.
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The table 'Astronomical Constants' has 19 more rows than appear in the book.
How to Cite this Reference
The recommended form of citation is:
John R. Rumble, ed., CRC Handbook of Chemistry and Physics, 103rd Edition (Internet Version 2022), CRC Press/Taylor & Francis, Boca Raton, FL.
If a specific table is cited, use the format: "Physical Constants of Organic Compounds," in CRC Handbook of Chemistry and Physics, 103rd Edition (Internet Version 2022), John R. Rumble, ed., CRC Press/Taylor & Francis, Boca Raton, FL.


The constants in this table are based originally on the set of constants adopted by the International Astronomical Union (IAU) in 1976. Updates have been made when new data were available (Refs. 1-8), with the latest updates being 2021. The left-most column of the table gives the most current reference for the cited value. All values are given in SI units; thus, masses are expressed in kilograms and distances in meters or kilometers as appropriate.

The astronomical unit of time is a time interval of one day (1 d) equal to 86400 s. An interval of 36525 d is one Julian century (1 cy). See Refs. 5-7 for an explanation of the way in which the various distance units used in astronomy are related.

Data on the Sun, the Earth, and other planets in the solar system are found in “Properties of the Solar System” in this section. Column definitions for the table are as follows.

Column heading Definition
Quantity Name of astronomical constant
Symbol Constant symbol
Value Value of astronomical constant
Uncertainty Uncertainty in value of constant
Units Units for value and uncertainty
Ref. Reference


  1. See “International System of Units” in Section 1.
  2. Astronomical Constants, Chapter K6 in The Astronomical Almanac 2019, Department of the Navy, Nautical Almanac Office, Washington, DC, 2018, retrieved January 31, 2021. <>
  3. Astronomical Constants, Solar System Dynamics, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, retrieved January 31, 2021. <>
  4. Pitjeva, E.V., J. Phys. Chem. Ref. Data 44, 031210, 2015. []
  5. Seidelmann, P. K., Explanatory Supplement to the Astronomical Almanac, University Science Books, Mill Valley, CA, 1990.
  6. Lang, K. R., Astrophysical Data: Planets and Stars, Springer-Verlag, New York, 1992. []
  7. International Astronomical Union, <>, 2012.
  8. Measuring the Universe - The IAU and Astronomical Units, <>.

Astronomical Constants

Continued on next page...
Defining constants
Astronomical unitau149 597 870 700exactm1
Speed of lightc299 792 458exactm s–11
Primary constants
Light-time for unit distance (1 au)τA499.004 783 836 ...exacts2
Equatorial radius of Earthae = 6 378 136.6 m ± 0.1ae = 6 378 136.6 m ± 0.1
Polar radius of Earthap = 6 356 752 map = 6 356 752 m
Dynamical form factor for EarthJ2 = 0.001 082 635 9 ± 1 × 10-10J2 = 0.001 082 635 9 ± 1 × 10-10
Geocentric gravitational constantGE3.986 004 418 × 1014± 8 × 105m3 s–22
Constant of gravitationG6.674 28 × 10–11± 000 067 × 10–11m3 kg–1 s–22
Ratio of mass of moon to that of Earthµ = 0.012 300 0371 ± 4 × 10-10µ = 0.012 300 0371 ± 4 × 10-10
Ratio of mass of Earth to that of the moon1/µ = 81.300 568 ± 3 × 10-61/µ = 81.300 568 ± 3 × 10-6
General precession in longitude, per Julian century, at standard epoch J2000ρ = 5028.796 195 arcsec/Julian Centuryρ = 5028.796 195 arcsec/Julian Century
Obliquity of the ecliptic at standard epoch J2000ε23°26′21″.4482
Derived constants
Constant of nutation at standard epoch J2000N9″.2052 3312
Solar parallax (π0 = arcsin(ae/ua))π08″.794 1432
Constant of aberration for standard epoch J2000κ20″.495 512
Flattening factor for Earthƒ = 1/298.256 42 = 0.003352820ƒ = 1/298.256 42 = 0.003352820
Heliocentric gravitational constant (GS = A3k2/D2)GS1.327 124 400 18 × 1020 ± 8 × 109 m3 s–23
GS1.327 124 400 42 × 1020± 10 × 109m3 s–24
Derived constants
Ratio of mass of sun to that of Earth (S/E) = (GS)/(GE))S/E = 332 946.048 7S/E = 332 946.048 7

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