# Physical Constants, Variables, and Model Parameters

 Symbol Definition Template_Name To insert the symbol associated with a given physical variable or constant into the text of any Wiki document, type ... {{ User:Tohline/Math/Template_Name }} $~c$ Speed of light;    Authoritative Value x0063 $~G$ Newtonian gravitational constant;    Authoritative Value x0047 $~h$ Planck constant;    Authoritative Value Note: $\hbar \equiv \frac{h}{2\pi}$ x0068 $~k$ Boltzmann constant;    Authoritative Value x006B $~N_A$ Avogadro constant;    Authoritative Value $~m_e$ Electron mass;    Authoritative Value $~m_p$ Proton mass;    Authoritative Value $~m_u$ Atomic mass unit;    Authoritative Value;    NOTE: mp / mu = 1.007276 $~\Re$ Gas constant = $~k$$~N_A$ = 1.007276 $~k$/$~m_p$;    Authoritative Value x211C $~A_\mathrm{F}$ Characteristic Fermi pressure; $A_\mathrm{F} \equiv \frac{\pi m_e^4 c^5}{3h^3} = 6.00228\times 10^{22}~\mathrm{erg}~\mathrm{cm}^{-3}$ Reference (original): Chandraskehar, S. (1935) Reference (recent): See Appendix of Even & Tohline (2009) Reference (authoritative book): [C67] $~B_\mathrm{F}$ Characteristic Fermi density; $\frac{B_\mathrm{F}}{\mu_e} \equiv \frac{8\pi m_p}{3} \biggl( \frac{m_e c}{h} \biggr)^3 = 9.81011\times 10^{5}~\mathrm{g}~\mathrm{cm}^{-3}$ Reference (original): Chandraskehar, S. (1935) Reference (recent): See Appendix of Even & Tohline (2009) Reference (authoritative book): [C67] $~a_\mathrm{rad}$ Radiation constant;    Authoritative Value $a_\mathrm{rad} \equiv \frac{8\pi^5}{15}\frac{k^4}{(hc)^3} = 7.56576\times 10^{-15}~\mathrm{erg}~\mathrm{cm}^{-3}~\mathrm{K}^{-4}$ $~T_e$ Temperature associated with the rest-mass energy of the electron;    Context of Definition $T_e \equiv \frac{m_e c^2}{k} = 5.9381\times 10^{9}~\mathrm{K}$ $~e$ Charge on an electron;    Authoritative Value The cgs units (statcoulombs) are equivalent to $(\mathrm{g}~\mathrm{cm}^3~\mathrm{s}^{-2})^{1/2}$ $~\alpha_\mathrm{fs}$ Fine structure constant (dimensionless);    Authoritative Value $\alpha_\mathrm{fs} \equiv \frac{e^2}{\hbar c} = \frac{1}{137.0359997}$ $~\sigma_T$ Thompson cross-section;    Authoritative Value $\sigma_T \equiv \frac{8\pi}{3} \biggl(\frac{\alpha_\mathrm{fs} \hbar}{m_e c} \biggr)^2 = 0.6652458\times 10^{-24}~\mathrm{cm}^2$ $~n_g$ Number density of gas particles;    units of "1/volume" x004E $~\rho$ Mass density;    units of "mass/volume" x03C1 $~V$ Specific Volume = 1/$~\rho$;    units of "volume/mass" x0056 $~\Phi$ Newtonian gravitational potential;    units of "energy/mass" or "velocity-squared" x03A6 $~H$ Enthalpy;    units of "energy/mass" or "velocity-squared" x0048 $~P$ Pressure;    units of "force/area" or "energy/volume" x0050 $~\epsilon$ Specific internal energy;    units of "energy/mass" or "velocity-squared" x03B5 $~s$ Specific entropy; x0073 $~t$ Time x0074 $~T$ Temperature;    units of "Kelvin" x0054 $~\vec{v}$ Euclidean 3-space velocity vector;    units of "length/time" $~\vec{x}$ Euclidean 3-space position vector $~\gamma_\mathrm{g}$ Adiabatic Index (or Ratio of Specific Heats); dimensionless    Wikipedia Discussion $~\bar{\mu}$ Mean molecular weight; dimensionless;    defined such that $~\bar{\mu}$ = $~\rho$/($~m_u$$~n_g$ ). x03BC $~\mu_e$ Molecular weight of electrons; dimensionless; defined such that $~\mu_e$ = $~\rho$/($~m_u$ Ne), where Ne is the number density of electrons. x03BC $~n$ Polytropic Index; dimensionless    Wikipedia Discussion x006E $~K_\mathrm{n}$ Polytropic Constant; dimensions depend on choice of $~n$    Wikipedia Discussion

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