Constants#

The astropy.constants module contains measured physical constants, for example the gravitational constant:

from astropy import constants as c

print(c.G)

---------------------------------------------------------------------------
ModuleNotFoundError                       Traceback (most recent call last)
Cell In[1], line 1
----> 1 from astropy import constants as c
      3 print(c.G)

ModuleNotFoundError: No module named 'astropy'

These constants can be treated as quantities.

See the documentation for the list of constants available:

Name

Value

Unit

Description

G

6.6743e-11

m3 / (kg s2)

Gravitational constant

N_A

6.02214076e+23

1 / (mol)

Avogadro’s number

R

8.31446262

J / (K mol)

Gas constant

Ryd

10973731.6

1 / (m)

Rydberg constant

a0

5.29177211e-11

m

Bohr radius

alpha

0.00729735257

Fine-structure constant

atm

101325

Pa

Standard atmosphere

b_wien

0.00289777196

m K

Wien wavelength displacement law constant

c

299792458

m / (s)

Speed of light in vacuum

e

1.60217663e-19

C

Electron charge

eps0

8.85418781e-12

F/m

Vacuum electric permittivity

g0

9.80665

m / s2

Standard acceleration of gravity

h

6.62607015e-34

J s

Planck constant

hbar

1.05457182e-34

J s

Reduced Planck constant

k_B

1.380649e-23

J / (K)

Boltzmann constant

m_e

9.1093837e-31

kg

Electron mass

m_n

1.6749275e-27

kg

Neutron mass

m_p

1.67262192e-27

kg

Proton mass

mu0

1.25663706e-06

N/A2

Vacuum magnetic permeability

muB

9.27401008e-24

J/T

Bohr magneton

sigma_T

6.65245873e-29

m2

Thomson scattering cross-section

sigma_sb

5.67037442e-08

W / (K4 m2)

Stefan-Boltzmann constant

u

1.66053907e-27

kg

Atomic mass

GM_earth

3.986004e+14

m3 / (s2)

Nominal Earth mass parameter

GM_jup

1.2668653e+17

m3 / (s2)

Nominal Jupiter mass parameter

GM_sun

1.3271244e+20

m3 / (s2)

Nominal solar mass parameter

L_bol0

3.0128e+28

W

Luminosity for absolute bolometric magnitude 0

L_sun

3.828e+26

W

Nominal solar luminosity

M_earth

5.97216787e+24

kg

Earth mass

M_jup

1.8981246e+27

kg

Jupiter mass

M_sun

1.98840987e+30

kg

Solar mass

R_earth

6378100

m

Nominal Earth equatorial radius

R_jup

71492000

m

Nominal Jupiter equatorial radius

R_sun

695700000

m

Nominal solar radius

au

1.49597871e+11

m

Astronomical Unit

kpc

3.08567758e+19

m

Kiloparsec

pc

3.08567758e+16

m

Parsec