Lesson: AstroPy 提供提供許多內建常數, 用以計算

from astropy import constants as const
print(const.c) # print the information of speed of light
print("const.c.to('km/s')=", const.c.to('km/s'))  # print the speed of light with km/s unit
print("const.c.to('pc/yr')=", const.c.to('pc/yr'))  # print the speed of light with pc/yr unit
from astropy import units as u
F = (const.G * 3. * const.M_sun * 100 * u.kg) / (2.2 * u.au) ** 2 #caculate the gravity between 2 objects 
print(F.to(u.N)) 

result

  Name   = Speed of light in vacuum
  Value  = 299792458.0
  Uncertainty  = 0.0
  Unit  = m / s
  Reference = CODATA 2014
const.c.to('km/s')= 299792.458 km / s
const.c.to('pc/yr'= 0.3066013937879528 pc / yr
0.3675671602160826 N

Lesson: constant table

Name	Value	Unit	Description
G	6.67408e-11	m3 / (kg s2)	Gravitational constant
N_A	6.02214086e+23	1 / (mol)	Avogadro’s number
R	8.3144598	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	0.0028977729	m K	Wien wavelength displacement law constant
c	299792458	m / (s)	Speed of light in vacuum
e	1.60217662e-19	C	Electron charge
eps0	8.85418782e-12	F/m	Electric constant
g0	9.80665	m / s2	Standard acceleration of gravity
h	6.62607004e-34	J s	Planck constant
hbar	1.0545718e-34	J s	Reduced Planck constant
k_B	1.38064852e-23	J / (K)	Boltzmann constant
m_e	9.10938356e-31	kg	Electron mass
m_n	1.67492747e-27	kg	Neutron mass
m_p	1.6726219e-27	kg	Proton mass
mu0	1.25663706e-06	N/A2	Magnetic constant
muB	9.27400999e-24	J/T	Bohr magneton
sigma_T	6.65245872e-29	m2	Thomson scattering cross-section
sigma_sb	5.670367e-08	W / (K4 m2)	Stefan-Boltzmann constant
u	1.66053904e-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	5.97236473e+24	kg	Earth mass
M_jup	1.89818717e+27	kg	Jupiter mass
M_sun	1.98847542e+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

Lesson 3: units of cosmology

from astropy.cosmology import WMAP9 as cosmo
H0 = cosmo.H(0)
print("H0.value is ", H0.value)
print("H0.unit is ", H0.unit) 

output

H0.value 69.32
H0.unit km / (Mpc s)