old_contents: #constants.py
  """Declares physical constants for use in enterprise.
  Depends on numpy for base mathematical constants, and
  scipy.constants for physical constants.
  """
  
  from __future__ import (absolute_import, division,
                          print_function, unicode_literals)
  
  import numpy as np
  import scipy.constants as sc
  
  
  # mathematical constants from numpy
  # the log constants are useful for converting between log base 10 and e
  pi = np.pi
  e = np.e
  log10e = np.log10(np.e)
  ln10 = np.log(10.)
  
  # physical constancts in mks
  c = sc.speed_of_light
  G = sc.gravitational_constant
  h = sc.Planck
  
  # astronomical times in sec (and frequencies in Hz)
  yr = sc.Julian_year
  fyr = 1. / yr
  
  # astronomical distances in meters
  AU = sc.astronomical_unit
  ly = sc.light_year
  pc = sc.parsec
  kpc = pc * 1.e3
  Mpc = pc * 1.e6
  Gpc = pc * 1.e9
  
  # other useful conversions in mks
  erg = sc.erg
  
new_contents: #constants.py
  """Declares physical constants for use in enterprise.
  Depends on numpy for base mathematical constants, and
  scipy.constants for physical constants.
  """
  
  from __future__ import (absolute_import, division,
                          print_function, unicode_literals)
  
  import numpy as np
  import scipy.constants as sc
  
  
  # mathematical constants from numpy
  # the log constants are useful for converting between log base 10 and e
  pi = np.pi
  e = np.e
  log10e = np.log10(np.e)
  ln10 = np.log(10.)
  
  # physical constancts in mks
  c = sc.speed_of_light
  G = sc.gravitational_constant
  h = sc.Planck
  
  # astronomical times in sec (and frequencies in Hz)
  yr = sc.Julian_year
  day = sc.day
  fyr = 1. / yr
  
  # astronomical distances in meters
  AU = sc.astronomical_unit
  ly = sc.light_year
  pc = sc.parsec
  kpc = pc * 1.e3
  Mpc = pc * 1.e6
  Gpc = pc * 1.e9
  
  # solar mass in kg and m,s natural units
  GMsun = 1.327124400e11  # measured more precisely than Msun alone!
  Msun = GMsun / G
  Rsun = GMsun / (c**2)
  Tsun = GMsun / (c**3)
  
  # other useful conversions in mks
  erg = sc.erg
  
subject: add day and solar mass