Constants

Useful physical and astronomical constants.

utils.constants.C = 29979245800.0

The speed of light in cm/s (PDG 2018).

utils.constants.M_PROTON = 1.672621898e-24

The mass of a proton in gram (PDG 2018).

utils.constants.KB = 1.38064852e-16

The Boltzmann constant in erg/K (PDG 2018).

utils.constants.SIGMA_SB = 5.670367e-05

The Stefan-Boltzmann constant in erg/cm^2/s/K^4 (PDG 2018).

utils.constants.G_CGS = 6.67408e-08

The gravitational constant G in \({\rm cm}^3 / g / s^2\) (PDG 2018).

utils.constants.EV = 1.6021766208e-12

The energy 1 eV in erg (PDG 2018).

utils.constants.H = 6.62607004e-27

The planck constant in erg s (PDG 2018).

utils.constants.RYDBERG = 13.605693009

The Rydberg constant in eV (PDG 2018).

utils.constants.AU = 14959787070000.0

Astronomical unit (au) in centimeters (PDG 2018).

utils.constants.PC = 3.08567758149e+18

A parsec in centimeters (PDG 2018).

utils.constants.KPC = 3.08567758149e+21

A kiloparsec in centimeters (PDG 2018).

utils.constants.MPC = 3.08567758149e+24

A megaparsec in centimeters (PDG 2018).

utils.constants.YEAR = 31556925.2

A year in seconds (PDG 2018).

utils.constants.GYR = 3.15569252e+16

A gigayear in seconds (PDG 2018).

utils.constants.MSUN = 1.9884754153381438e+33

A solar mass, \(M_{\odot}\), in grams (IAU 2015).

utils.constants.G = 4.300917270038e-06

The gravitational constant G in \({\rm kpc} \ {\rm km}^2 / M_{\odot} / s^2\). This constant is computed from the cgs version but given with more significant digits to preserve consistency with the \({\rm Mpc}\) and \(M_{\odot}\) units.

utils.constants.RHO_CRIT_0_KPC3 = 277.536627245708

The critical density of the universe at z = 0 in units of \(M_{\odot} h^2 / {\rm kpc}^3\).

utils.constants.RHO_CRIT_0_MPC3 = 277536627245.708

The critical density of the universe at z = 0 in units of \(M_{\odot} h^2 / {\rm Mpc}^3\).

utils.constants.DELTA_COLLAPSE = 1.68647

The linear overdensity threshold for halo collapse according to the spherical top-hat collapse model (Gunn & Gott 1972). This number corresponds to \(3/5 (3\pi/2)^{2/3}\) and is modified very slightly in a non-EdS universe.