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General, commonly used functions for other projects.

Project description

Quickly calculate cosmological parameters.

  • Provides both command-line and API interfaces.
  • Uses the machinery from the astropy.cosmology package.

The user provides an input parameter (e.g. redshift or luminosity-distance) and recieves the entire set of cosmological measures corresponding to the epoch thus specified.

The below gif shows three examples: inputting a redshift, a luminosity distance (-dl 400Mpc), and an age of the universe (-ta 3.2Gyr).


Using pip:

pip install cosmopy

From source:

git clone
pip install cosmopy


cosmopy can be used via the command-line cosmo command, or via python API by importing the module directly.

  • Command Line:

    $ cosmo --help
     usage: cosmo [-h] [-z Z] [-a A] [-dc DC] [-dl DL] [-tl TL] [-ta TA] [-v]
     cosmopy: cosmological calculator.
     optional arguments:
       -h, --help      show this help message and exit
       -z Z            target redshift z
       -a A            target scale factor a
       -dc DC, -cd DC  target coming distance D_C
       -dl DL, -ld DL  target luminosity distance D_L
       -tl TL, -lt TL  target look-back time T_L
       -ta TA, -at TA  target universe age T_A
       -v, --version   print version information.

    For example, entering an input redshift of 0.2:

    $ cosmo -z 0.2
           z = 0.2000                                : Redshift
           a = 0.8333                                : Scale-factor
         D_c = 815.3960 Mpc      ~ 2.5160e+27 cm     : Comoving Distance
         D_L = 978.4752 Mpc      ~ 3.0193e+27 cm     : Luminosity Distance
         D_A = 679.4967 Mpc      ~ 2.0967e+27 cm     : Angular Diameter Distance
      Arcsec = 3294.2928 pc      ~ 1.0165e+22 cm     : Arcsecond Scale
        T_lb = 2.4277 Gyr        ~ 7.6613e+16 s      : Lookback Time
         T_a = 11.3235 Gyr       ~ 3.5734e+17 s      : Age of the Universe
          DM = 39.9527                               : Distance Modulus

    or an input luminosity-distance of 400 Mpc:

    $ cosmo -dl 400Mpc
           z = 0.0880                                : Redshift
           a = 0.9192                                : Scale-factor
         D_c = 367.6631 Mpc      ~ 1.1345e+27 cm     : Comoving Distance
         D_L = 400.0000 Mpc      ~ 1.2343e+27 cm     : Luminosity Distance
         D_A = 337.9403 Mpc      ~ 1.0428e+27 cm     : Angular Diameter Distance
      Arcsec = 1638.3809 pc      ~ 5.0555e+21 cm     : Arcsecond Scale
        T_lb = 1.1496 Gyr        ~ 3.6280e+16 s      : Lookback Time
         T_a = 12.6016 Gyr       ~ 3.9768e+17 s      : Age of the Universe
          DM = 38.0103                               : Distance Modulus
  • Python API

    The module can be imported as cosmopy, from which the primary access point is the api function which accepts two arguments: a key (a target cosmological parameter) and a value of that parameter (optionally including units). The function returns a dictionary with the computed values as key: value pairs (both strings). For example:

    $ python -c "import cosmopy; print(cosmopy.api('dl', '1.2 Gpc'))"
     {'z': '0.2396', 'dl': '1200.0000 Mpc', 'tl': '2.8359 Gyr', 'dc': '968.0336 Mpc', 'ta': '10.9153 Gyr', 'da': '780.9075 Mpc', 'dm': '40.3959', 'arc': '3785.9464 pc', 'a': '0.8067'}

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