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 ${\mathrm{c}\mathrm{m}}^3/g/s^2$ (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 $\mathrm{k}\mathrm{p}\mathrm{c}{\mathrm{k}\mathrm{m}}^2/M_{\odot }/s^2$. This constant is computed from the cgs version but given with more significant digits to preserve consistency with the $\mathrm{M}\mathrm{p}\mathrm{c}$ and $M_{\odot }$ units.

utils.constants.RHO_CRIT_0_KPC3 = 277.536627245708#

The critical density of the universe at z = 0 in units of $M_{\odot }{h}^2/{\mathrm{k}\mathrm{p}\mathrm{c}}^3$.

utils.constants.RHO_CRIT_0_MPC3 = 277536627245.708#

The critical density of the universe at z = 0 in units of $M_{\odot }{h}^2/{\mathrm{M}\mathrm{p}\mathrm{c}}^3$.

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.