# 31.5: Some Useful Constants for Astronomy (Appendix E)

- Page ID
- 19716

Table \(\PageIndex{1}\): Physical Constants | |
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Name | Value |

speed of light (c) |
2.9979 × 10^{8} m/s |

gravitational constant (G) |
6.674 × 10^{−11} m^{3}/(kg s^{2}) |

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_{∞}) |
1.0974 × 10^{7} m^{−1} |

Stefan-Boltzmann constant (σ) | 5.670 × 10^{−8} J/(s·m^{2} deg^{4})^{1} |

Wien’s law constant (λ_{max}T) |
2.898 × 10^{−3} m K |

electron volt (energy) (eV) | 1.602 × 10^{−19} J |

energy equivalent of 1 ton TNT | 4.2 × 10^{9} J |

Table \(\PageIndex{2}\): Astronomical Constants | |
---|---|

Name | Value |

astronomical unit (AU) | 1.496 × 10^{11} m |

Light-year (ly) | 9.461 × 10^{15} m |

parsec (pc) | 3.086 × 10^{16} m = 3.262 light-years |

sidereal year (y) | 3.156 × 10^{7} s |

mass of Earth (M_{Earth}) |
5.974 × 10^{24} kg |

equatorial radius of Earth (R_{Earth}) |
6.378 × 10^{6} m |

obliquity of ecliptic | 23° 26’ |

surface gravity of Earth (g) |
9.807 m/s^{2} |

escape velocity of Earth (v_{Earth}) |
1.119 × 10^{4} m/s |

mass of Sun (M_{Sun}) |
1.989 × 10^{30} kg |

equatorial radius of Sun (R_{Sun}) |
6.960 × 10^{8} m |

luminosity of Sun (L_{Sun}) |
3.85 × 10^{26} W |

solar constant (flux of energy received at Earth) (S) | 1.368 × 10^{3} W/m^{2} |

Hubble constant (H_{0}) |
approximately 20 km/s per million light-years, or approximately 70 km/s per megaparsec |

## Footnotes

^{1}deg stands for degrees Celsius or kelvins