const.py

# physical constants

H_PLANCK = 6.6261e-27   # Planck constant
C_LIGHT = 2.99792e10  # speed of light
M_PROTON = 1.673e-24  # proton mass
ME = 9.1094e-28         # electron's rest mass
ME_over_MP = ME/M_PROTON
CHARGE_e = 4.80321e-10  # electron charge
A_RAD = 7.5646e-15      # radiation density constant
K_B = 1.3807e-16        # Boltzmann constant
SIGMA_SB = 5.6705e-5    # Stefan-Boltzmann constant
G_NEWTON = 6.674e-8     # Newton's constant

KAPPA_T = 0.34       # opacity from Thomson scattering
KAPPA_BF = 4.3e25   # bound-free opacity = KAPPA_BF*rho*T^(-3.5)
SIGMA_T = 6.65246e-25   # Thomson cross section

H_HUBBLE = 7.0e9/3.09e27   # Hubble's constant, in s^-1
OMEGA_M = 0.27      # cosmological mass fraction of matter
OMEGA_LAMBDA = 0.73     # cosmological constant

M_SUN = 1.98847e33      # solar mass
R_SUN = 6.96e10         # solar radius
kpc2cm = 3.0856776e21
pc2cm = 3.0856776e18
eV2erg = 1.60218e-12
erg2eV = 1./eV2erg
day2sec = 86400.
yr2sec = 365*day2sec
au2cm = 1.49597871e13
rad2arcsec = 206264.80624709

ME_C2 = 8.187e-7       # electron's rest mass energy