Skip to ContentGo to accessibility pageKeyboard shortcuts menu
OpenStax Logo
Astronomy 2e

E | Some Useful Constants for Astronomy

Astronomy 2eE | 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 (RR) 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
Table E1
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° 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
Table E2

Footnotes

  • 1deg stands for degrees Celsius or kelvins
Citation/Attribution

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Attribution information
  • If you are redistributing all or part of this book in a print format, then you must include on every physical page the following attribution:
    Access for free at https://openstax.org/books/astronomy-2e/pages/1-introduction
  • If you are redistributing all or part of this book in a digital format, then you must include on every digital page view the following attribution:
    Access for free at https://openstax.org/books/astronomy-2e/pages/1-introduction
Citation information

© Jul 8, 2024 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.