old_contents: # coding: utf-8
  
  from __future__ import division, print_function
  
  __author__ = "adrn <adrn@astro.columbia.edu>"
  
  # Standard library
  import os, sys
  import logging
  
  # Third-party
  import astropy.units as u
  
  # Create logger
  logger = logging.getLogger(__name__)
  
  # default unit system
  usys = dict()
  usys['length'] = u.kpc
  usys['speed'] = u.km/u.s
  usys['time'] = u.Myr
  usys['angular speed'] = u.mas/u.yr
  usys['angle'] = u.degree
  usys['mass'] = u.M_sun
  usys['dimensionless'] = u.dimensionless_unscaled
new_contents: # coding: utf-8
  
  from __future__ import division, print_function
  
  __author__ = "adrn <adrn@astro.columbia.edu>"
  
  # Standard library
  import os, sys
  import logging
  
  # Third-party
  import astropy.units as u
  
  # Create logger
  logger = logging.getLogger(__name__)
  
  # default unit system
  usys = dict()
  usys['length'] = u.kpc
  usys['speed'] = u.km/u.s
  usys['time'] = u.Myr
  usys['angular speed'] = u.mas/u.yr
  usys['angle'] = u.degree
  usys['mass'] = u.M_sun
  usys['dimensionless'] = u.dimensionless_unscaled
  
  # define galactic unit system
  galactic = (u.kpc, u.Myr, u.Msun, u.radian)
subject: add galactic usys