Some Useful Constants for Astronomy, Front matter | Astronomy 2e

Learning objectives

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 (M_H)	1.673 × 10⁻²⁷ kg
mass of an electron (M_e)	9.109 × 10⁻³¹ kg
Rydberg constant ( $R_{\infty}$ )	1.0974 × 10⁷ m⁻¹
Stefan-Boltzmann constant (σ)	5.670 × 10⁻⁸ J/(s·m² deg⁴)deg stands for degrees Celsius or kelvins
Wien’s law constant (λ_maxT)	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 (M_Earth)	5.974 × 10²⁴ kg
equatorial radius of Earth (R_Earth)	6.378 × 10⁶ m
obliquity of ecliptic	23° 26’
surface gravity of Earth (g)	9.807 m/s²
escape velocity of Earth (v_Earth)	1.119 × 10⁴ m/s
mass of Sun (M_Sun)	1.989 × 10³⁰ kg
equatorial radius of Sun (R_Sun)	6.960 × 10⁸ m
luminosity of Sun (L_Sun)	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

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