Detail: more  less Quantity Symbol Value and units astronomical unit AU 1.496E+13 cm atomic mass unit, m(12C)/12 u 1.661E-24 gm Avogadro's number NA 6.022E+23 mole-1 Boltzmann's constant k 1.381E-16 erg K-1 day day 8.640E+04 s day, sidereal   8.616E+04 s electron mass me 9.109E-28 gm elementary charge qe 4.803E-10 esu fine-structure constant α 7.297E-03 1/α 1.370E+02 hydrogen atomic mass (in populations) mH 1.008 u hydrogen molecular mass (in populations) mH2 2.016 u light year ly 9.461E+17 cm neutron mass mn 1.675E-24 gm 1.009E+00 u Newton's constant of gravitation G 6.674E-08 cm3 gm-1 s-2 parsec pc 1.377E-02 cm Planck's constant h 6.626E-27 erg s   ħ = h/2π 1.055E-27 erg s proton mass mp 1.673E-24 gm 1.007E+00 u solar irradiance at Earth fÅ 1.361E+06 erg s-1 cm-2 solar luminosity Le 3.828E+33 erg s-1 solar mass Me 1.988E+33 gm solar mass parameter GMe 1.327E+26 dyne cm2 solar photospheric radius Re 6.957E+10 cm solar photospheric temperature Tee 5.771E+03 K speed of light in vacuum c 2.998E+10 cm s-1 standard acceleration of gravity g 9.807E+02 cm s-2 standard atmospheric pressure atm 1.013E+06 dyne cm-2 Stefan-Boltzmann constant σ 5.670E-05 erg s-1 cm-2 K-4 vacuum electric permittivity ε0 no such thing in cgs vacuum magnetic permeability μ0 no such thing in cgs year, sidereal   3.156E+07 s year, tropical yr 3.156E+07 s