# nature.py - Information about the universe around us.
#
# Version of 2006-02-20.
#
"""
Constants of nature, attached to units.


Here are some examples of the use of this package.



Example 1: have you ever wondered about the magnitude of
the centrifugal force due to the Earth's rotation when you're
standing on the equator?

>>> import nature
>>> r = nature.earth_equatorial_radius
>>> w = 2 * 3.1416 / nature.earth_rotation_period
>>> print w*w*r
3.39172088527 cm /sec^2



Example 2: did you know the Sun pulls on the Moon harder
than the Earth does?

>>> G = nature.gravitational_constant
>>> re = nature.moon_orbit_radius             # Moon-Earth distance
>>> rs = ( nature.earth_orbit_radius + re )   # Moon farthest from sun.
>>> ms = nature.sun_mass
>>> me = nature.earth_mass
>>> print "Earth pull:", G*me/re/re
Earth pull: 0.27021048893 cm /sec^2

>>> print "Sun pull:", G*ms/rs/rs
Sun pull: 0.585397316513 cm /sec^2            # About twice Earth's pull.



Example 3: We address the question, "If 'natural' units
are such that Plank's constant, the speed of light, and
the gravitational constant all take the value of unity,
then what is the natural unit of mass?"

>>> h = nature.plancks_constant
>>> c = nature.speed_of_light
>>> G = nature.gravitational_constant
>>> print h                       # First, we will note the units of
6.6262e-27 g cm^2 /sec            # the three basic quantities . . .

>>> print c
29979250000.0 cm /sec

>>> print G
6.6732e-08 cm^3 /g /sec^2

>>> print h/G                     # Guessing a step in the right direction
9.92956902236e-20 g^2 sec /cm     # gets us within sight of our objective.

>>> print h*c/G
2.97681032114e-09 g^2             # We see that hc/G has units of grams^2.

>>> print nature.sqrt( h*c/G )
5.4560153236e-05 g                # ... so this is the natural unit of mass.



Using the "units" module, you can convert numbers to
other units:

>>> import units
>>> r = nature.moon_radius
>>> print 2 * r / units.mile
2159.88626422                     # Moon's diameter, in miles.
"""


import units

g = units.gram
cm = units.centimeter
s = units.second
day = units.day
k = units.kelvin
coulomb = units.coulomb
erg = units.erg
sqrt = units.sqrt

avogadros_number = 6.02257e23
speed_of_light = 2.997925e10 * cm / s
electron_charge = 1.60219e-19 * coulomb
plancks_constant = 6.6262e-27 * erg * s
electron_rest_mass = 9.1096e-28 * g
fine_structure_constant = 7.297351e-3
proton_mass = 1.672614e-24 * g
neutron_mass = 1.674920e-24 * g
mu_e = 9.284851e-21     # Electron magnetic moment, erg/Gauss
gas_constant_mol = 8.31434e7 * erg / k
boltzmanns_constant = 1.380622e-16 * erg / k
stefan_boltzmann_constant = 5.66961e-5 * erg/s/cm/cm/k/k/k/k
gravitational_constant = 6.6732e-8 * erg*cm/g/g
atomic_mass_unit = 1.65979e-24 * g
earth_surface_gravity = 980 * cm/s/s # Gravity on Earth's surface, lat = 38N.

earth_mass = 5.983e27 * g
earth_polar_radius = 6.35691e8 * cm
earth_equatorial_radius = 6.378390e8 * cm
earth_radius = 6.37122e8 * cm
earth_land_area = 148.847e16 * cm * cm
earth_orbit_radius = 1.495e13 * cm
earth_orbit_period = 365.24 * day
earth_rotation_period = day * ( 1 - 1 / ( 1 + earth_orbit_period / day ) )
moon_mass = 0.01228 * earth_mass
moon_radius = 3476.e5/2 * cm
moon_orbit_radius = 3.84393e10 * cm
moon_orbit_period = 27.32 * day
sun_mass = 3.2939e5 * earth_mass
sun_radius = 1.3906e11/2 * cm