Selected Astronomical Constants, 2020
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This is the ASCII version of pages K6-K7 of The Astronomical Almanac 2020. The following nomenclature is used in this file:
(a) greek letters, as in TeX, are spelt out, e.g., alpha,
(b) the symbols ^ and _ are used (as in TeX) to indicate superscripts and subscripts, respectively,
(c) the symbols *, / and +/- denote multiplication, division, and plus-minus uncertainty bounds, respectively, and
(d) numerical exponents are given with the Fortran D format.
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| The IAU 2009 System of Astronomical Constants (1) published in the IAU WG report on Numerical Standards for |
| Fundamental Astronomy (NSFA, 2011) and updated by resolution B2 of the IAU XXVIII General Assembly (2012), (2) planetary |
| equatorial radii, from the IAU WG report on Cartographic Coordinates and Rotational Elements: 2015 (2017), and (3) |
| other useful constants. Tabulated for each quantity is its description, symbol and value, and, as appropriate, its |
| uncertainty in units in which the quantity is given. Further information is given at the end of this file. |
| |
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| | Description of Quantity | Symbol = Value | Unit | Uncertainty |
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|1 | IAU 2009/2012 System of Astronomical Constants# |
| |---------------------------------------------------------------------------------------------------------------------------|
|1.1|Natural Defining Constant: | | | |
| | Speed of light | c = 299792458 | m/s | |
| |-------------------------------------------|----------------------------------------|------------------------|-------------|
|1.2|Auxiliary Defining Constants: | | | |
| | Astronomical unit (unit distance)## | au =A = 149597870700 | m | |
| | 1-d(TT)/d(TCG) | L_G = 6.969290134D-10 | | |
| | 1-d(TDB)/d(TCB) | L_B = 1.550519768D-08 | | |
| | TDB-TCB at T_0 = 2443144.5003725 (TCB) | TDB_0 = -6.55D-05 | s | |
| | Earth rotation angle (ERA) at J2000.0 UT1 | theta_0 = 0.7790572732640 | revolutions | |
| | Rate of advance of ERA | d(theta)/dUT1 = 1.00273781191135448 | revs/UT1-day | |
| |-------------------------------------------|----------------------------------------|------------------------|-------------|
|1.3|Natural Measurable Constant: | | | |
| | Constant of gravitation | G = 6.67428D-11 | m^3/kg/s^2 | +/- 6.7D-15 |
| |-------------------------------------------|----------------------------------------|------------------------|-------------|
|1.4|Other Constants: | | | |
| | Average value of 1-d(TCG)/d(TCB) | L_C = 1.48082686741D-08 | | +/- 2D-17 |
| |-------------------------------------------|----------------------------------------|------------------------|-------------|
|1.5|Body Constants: | | | |
| | Solar mass parameter## | GMS = 1.32712442099D20 | m^3/s^2 (TCB) | +/- 1D10 |
| | | = 1.32712440041D20 | m^3/s^2 (TDB) | +/- 1D10 |
| | Equatorial radius for Earth | a_E = a_e = 6378136.6 | m (TT) | +/- 0.1 |
| | Dynamical form-factor for the Earth | J_2 = 0.0010826359 | | +/- 1D-10 |
| | Long-term variation in J_2 | \dot{J_2} = -3.0D-09 | per cy | +/- 6D-10 |
| | Geocentric gravitational constant | GME = 3.986004418D14 | m^3/s^2 (TCB) | +/- 8D05 |
| | | = 3.986004415D14 | m^3/s^2 (TT) | +/- 8D05 |
| | | = 3.986004356D14 | m^3/s^2 (TDB) | +/- 8D05 |
| | Potential of the geoid### | W_0 = 6.26368560D07 | m^2/s^2 | +/- 0.5 |
| | Nominal mean angular vel.of Earth rotation| omega = 7.292115D-05 | rad/s (TT) | |
| | Mass Ratio: Moon to Earth | M_M / M_E = 1.23000371D-02 | | +/- 4D-10 |
| |-------------------------------------------|----------------------------------------|------------------------|-------------|
| | Ratio of the Mass of the Sun to the Mass of the Body* | | |
| | Mass Ratio: Sun to Mercury#### | M_S / M_Me = 6.0236D06 | | +/- 3D02 |
| | Mass Ratio: Sun to Venus | M_S / M_Ve = 4.08523719D05 | | +/- 8D-03 |
| | Mass Ratio: Sun to Mars | M_S / M_Ma = 3.09870359D06 | | +/- 2D-02 |
| | Mass Ratio: Sun to Jupiter | M_S / M_J = 1.047348644D03 | | +/- 1.7D-05 |
| | Mass Ratio: Sun to Saturn | M_S / M_Sa = 3.4979018D03 | | +/- 1D-04 |
| | Mass Ratio: Sun to Uranus#### | M_S / M_U = 2.290298D04 | | +/- 3D-02 |
| | Mass Ratio: Sun to Neptune | M_S / M_N = 1.941226D04 | | +/- 3D-02 |
| | Mass Ratio: Sun to (134340) Pluto#### | M_S / M_P = 1.36566D08 | | +/- 2.8D04 |
| | Mass Ratio: Sun to (136199) Eris | M_S / M_Eris = 1.191D08 | | +/- 1.4D06 |
| | | | | |
| | *All values of the masses from Mars to Eris are the sum of the masses of the celestial bodies and its satellites. |
| |-------------------------------------------|----------------------------------------|------------------------|-------------|
| | Ratio of the Mass of the Body to the Mass of the Sun | | |
| | Mass Ratio: (1) Ceres to Sun | M_Ceres /M_S = 4.72D-10 | | +/- 3D-12 |
| | Mass Ratio: (2) Pallas to Sun | M_Pallas /M_S = 1.03D-10 | | +/- 3D-12 |
| | Mass Ratio: (4) Vesta to Sun#### | M_Vesta /M_S = 1.35D-10 | | +/- 3D-12 |
| |-------------------------------------------|----------------------------------------|------------------------|-------------|
|1.6|Initial Values at J2000.0: | | | |
| | Mean obliquity of the ecliptic, epsilon_0 | epsilon_J2000.0 = 23 26 21.406 | o ' " | |
| | | = 84381.406 | " | +/- 0.001 |
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|2 |Constants from IAU WG on Cartographic Coordinates and Rotational Elements: 2015 |
| |---------------------------------------------------------------------------------------------------------------------------|
| | Equatorial radii: | | | |
| | Mercury | = 2440.53 | km | +/- 0.04 |
| | Venus | = 6051.8 | km | +/- 1.0 |
| | Earth | = 6378.1366 | km | +/- 0.0001 |
| | Mars | = 3396.19 | km | +/- 0.1 |
| | Jupiter | = 71492 | km | +/- 4 |
| | Saturn | = 60268 | km | +/- 4 |
| | Uranus | = 25559 | km | +/- 4 |
| | Neptune | = 24764 | km | +/- 15 |
| | (134340) Pluto | = 1188.3 | km | +/- 1.6 |
| | Moon (mean) | = 1737.4 | km | +/- 1 |
| | Sun##### | = 696000 | km | |
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|3 |Other Constants |
| |---------------------------------------------------------------------------------------------------------------------------|
| | Light-time for unit distance## | tau_A = au/c = 499.00478384 | s | |
| | | 1/tau_A = 173.144632674 | au/d | |
| | | | | |
| | Mass Ratio: Earth to Moon | M_E/M_M = 1/mu = 81.300568 | | +/- 3D-06 |
| | Mass Ratio: Sun to Earth | GMS/GME = 332946.0487 | | +/- 7D-04 |
| | Mass of the Sun | M_S = S = GMS/G = 1.9884D30 | kg | +/- 2D26 |
| | Mass of the Earth | M_E = E = GME/G = 5.9722D24 | kg | +/- 6D20 |
| | Mass Ratio: Sun to Earth + Moon | (S/E)/(1 + mu) = 328900.5596 | | +/- 7D-04 |
| | | | | |
| | Earth, reciprocal of flattening IERS 2010 | 1/f = 298.25642 | | +/- 1D-05 |
| | | | | |
| | Rates of precession at J2000.0 (IAU 2006) | | | |
| | General precession in longitude | p_A = 5028.796195 | "/Julian century (TDB) | |
| | Rate of change in obliquity | d(epsilon)/dT = -46.836769 | "/Julian century (TDB) | |
| | Precession of the equator in longitude | d(psi)/dT = 5038.481507 | "/Julian century (TDB) | |
| | Precession of the equator in obliquity | d(omega)/dT = -0.025754 | "/Julian century (TDB) | |
| | | | | |
| | Constant of nutation at epoch J2000.0 | N = 9.2052331 | " | |
| | Solar parallax, pi_odot | sin^-1(a_e/au) = 8.794143 | " | |
| | Constant of aberration at epoch J2000.0 | kappa = 20.49551 | " | |
| | | | | |
| | Masses of the larger natural satellites: | | | |
| | Mass satellite/mass of the planet | | | |
| | Jupiter: Io | = 4.705D-05 | | |
| | Europa | = 2.528D-05 | | |
| | Ganymede | = 7.805D-05 | | |
| | Callisto | = 5.667D-05 | | |
| | Saturn: Titan | = 2.367D-04 | | |
| | Uranus: Ariel | = 1.49D-05 | | |
| | Umbriel | = 1.41D-05 | | |
| | Titania | = 3.94D-05 | | |
| | Oberon | = 3.32D-05 | | |
| | Neptune: Triton | = 2.089D-04 | | |
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| The IAU Working Group on Numerical Standards for Fundamental Astronomy maintains a website, see http://asa.hmnao.com, |
| which contains an agreed list of `Current Best Estimates' together with detailed information about the constants, and |
| relevant references. See footnotes below for more details. |
| |
| This almanac, in certain circumstances, may not use constants from this list. The reasons and those constants used will be |
| given at the end of Section L Notes and References. |
| |
| The units meter (m), kilogram (kg), and SI second (s) are the units of length, mass and time in the International System of |
| Units (SI). |
| |
| The astronomical unit of time is a time interval of one day (D) of 86400 seconds. An interval of 36525 days is one Julian |
| century. Some constants that involve time, either directly or indirectly need to be compatible with the underlying time |
| scales, for example TDB-compatible. To specify the time scale that the value of the constant is compatible with, (TDB), (TCB) |
| or (TT) is included after the unit. |
| |
| #The IAU 2009 System of Astronomical Constants classifies the constants into the groups shown. This may be redefined and |
| users should check the NSFA website for updates. |
| |
| ##The astronomical unit of length (au) in metres is re-defined as a conventional unit of length (resolution B2, IAU XXVIII GA |
| 2012) in agreement with the value adopted by IAU 2009 Resolution B2; it is to be used with all time scales such as TCB, TDB, |
| TCG, TT, etc. Also the heliocentric gravitational constant GMS is renamed the solar mass parameter. Further details are |
| given in Section L Notes and References. |
| |
| ###The International Association of Geodesy 2015 Resolution No. 1 adopted an updated value. |
| |
| ####In May 2015 new best estimates were agreed (see http://asa.hmnao.com). Values printed here are those of the IAU 2009 |
| System of Astronomical Constants. |
| |
| #####The value printed here is that from the report of the IAU WG on Cartographic Coordinates and Rotational Elements: 2009 |
| (2011) and is the value used throughout this almanac. Further details are given in Section L Notes and References. |
| |
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| 2018 March 8 |
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