# Physical Constants


Name Symbol Value Unit
Number $$\pi$$ $$\pi$$ 3.14159265358979323846
Number e e 2.71828182845904523536
Euler’s constant   0.577215664901532860606
Elementary charge $$e$$ $$1.60217733\cdot10^{-19}$$

C

Gravitational constant $$G,\kappa$$ $$6.67259\cdot10^{-11}$$ m$$^3$$kg$$^{-1}$$s$$^{-2}$$
Fine-structure constant $$\alpha=e^2/2hc\varepsilon_0$$ $$\approx1/137$$
Speed of light in vacuum $$c$$ $$2.99792458\cdot10^8$$ m/s (def)
Permittivity of the vacuum $$\varepsilon_0$$ $$8.854187\cdot10^{-12}$$ F/m
Permeability of the vacuum $$\mu_0$$ $$4\pi\cdot10^{-7}$$ H/m
$$(4\pi\varepsilon_0)^{-1}$$   $$8.9876\cdot10^9$$ Nm$$^2$$C$$^{-2}$$
Planck’s constant $$h$$ $$6.6260755\cdot10^{-34}$$

Js

Dirac’s constant $$\hbar=h/2\pi$$ $$1.0545727\cdot10^{-34}$$ Js
Bohr magneton $$\mu_{\rm B}=e\hbar/2m_{\rm e}$$ $$9.2741\cdot10^{-24}$$ Am$$^2$$
Bohr radius $$a_0$$ $$0.52918$$ Å
Rydberg’s constant $$Ry$$ 13.595 eV
Electron Compton wavelength $$\lambda_{\rm Ce}=h/m_{\rm e}c$$ $$2.2463\cdot10^{-12}$$ m
Proton Compton wavelength $$\lambda_{\rm Cp}=h/m_{\rm p}c$$ $$1.3214\cdot10^{-15}$$ m
Reduced mass of the H-atom $$\mu_{\rm H}$$ $$9.1045755\cdot10^{-31}$$ kg
Stefan-Boltzmann’s constant $$\sigma$$ $$5.67032\cdot10^{-8}$$

Wm$$^{-2}$$K$$^{-4}$$

Wien’s constant $$k_{\rm W}$$ $$2.8978\cdot10^{-3}$$ mK
Molar gasconstant $$R$$ 8.31441 J$$\cdot$$mol$$^{-1}\cdot$$K$$^{-1}$$
Avogadro’s constant $$N_{\rm A}$$ $$6.0221367\cdot10^{23}$$ mol$$^{-1}$$
Boltzmann’s constant $$k=R/N_{\rm A}$$ $$1.380658\cdot10^{-23}$$ J/K
Electron mass $$m_{\rm e}$$ $$9.1093897\cdot10^{-31}$$

kg

Proton mass $$m_{\rm p}$$ $$1.6726231\cdot10^{-27}$$ kg
Neutron mass $$m_{\rm n}$$ $$1.674954\cdot10^{-27}$$ kg
Elementary mass unit $$m_{\rm u}=\frac{1}{12}m(^{12}_{~6}$$C) $$1.6605656\cdot10^{-27}$$ kg
Nuclear magneton $$\mu_{\rm N}$$ $$5.0508\cdot10^{-27}$$ J/T
Diameter of the Sun $$D_\odot$$ $$1392\cdot10^6$$

m

Mass of the Sun $$M_\odot$$ $$1.989\cdot10^{30}$$ kg
Rotational period of the Sun $$T_\odot$$ 25.38 days
Radius of Earth $$R_{\rm A}$$ $$6.378\cdot10^6$$ m
Mass of Earth $$M_{\rm A}$$ $$5.976\cdot10^{24}$$ kg
Rotational period of Earth $$T_{\rm A}$$ 23.96 hours
Earth orbital period Tropical year 365.24219879 days
Astronomical unit AU $$1.4959787066\cdot10^{11}$$ m
Light year lj $$9.4605\cdot10^{15}$$ m
Parsec pc $$3.0857\cdot10^{16}$$ m
Hubble constant $$H$$ $$\approx(75\pm25)$$ km$$\cdot$$s$$^{-1}\cdot$$Mpc$$^{-1}$$
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This page titled Physical Constants is shared under a CC BY license and was authored, remixed, and/or curated by Johan Wevers.