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A.5 Some Useful Constants for Astronomy

Physical Constants
Name Value
speed of light (c) 2.9979 × 108 m/s
gravitational constant (G) 6.674 × 10−11 m3/(kg s2)
Planck’s constant (h) 6.626 × 10−34 J-s
mass of a hydrogen atom (MH) 1.673 × 10−27 kg
mass of an electron (Me) 9.109 × 10−31 kg
Rydberg constant (R∞R∞) 1.0974 × 107 m−1
Stefan-Boltzmann constant (σ) 5.670 × 10−8 J/(s·m2 deg4)1
Wien’s law constant (λmaxT) 2.898 × 10−3 m K
electron volt (energy) (eV) 1.602 × 10−19 J
energy equivalent of 1 ton TNT 4.2 × 109 J
Astronomical Constants
Name Value
astronomical unit (AU) 1.496 × 1011 m
Light-year (ly) 9.461 × 1015 m
parsec (pc) 3.086 × 1016 m = 3.262 light-years
sidereal year (y) 3.156 × 107 s
mass of Earth (MEarth) 5.974 × 1024 kg
equatorial radius of Earth (REarth) 6.378 × 106 m
obliquity of ecliptic 23.4° 26’
surface gravity of Earth (g) 9.807 m/s2
escape velocity of Earth (vEarth) 1.119 × 104 m/s
mass of Sun (MSun) 1.989 × 1030 kg
equatorial radius of Sun (RSun) 6.960 × 108 m
luminosity of Sun (LSun) 3.85 × 1026 W
solar constant (flux of energy received at Earth) (S) 1.368 × 103 W/m2
Hubble constant (H0) approximately 20 km/s per million light-years, or approximately 70 km/s per megaparsec

Footnotes

  1. 1 deg stands for degrees Celsius or kelvins

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