In [2]:
%matplotlib inline
import warnings
In [3]:
from IPython.display import Image
In [4]:
from IPython.display import HTML

Steve Crawford

(one small member of the much larger astropy community)

Philosopy of Astropy

Contributors of Astropy

Astropy v0.4 and affiliate packages

How to Contribute

History and Motivation

Philosophy of Astropy

The Astropy Project is a community effort to develop a core package for Astronomy in Python and foster interoperability between Python astronomy packages.

  • Minimize duplication
  • Create a well-documented and tested core astronomy library
  • Create frameworks for producing astronomy related code
  • Build and Support Python Astronomy Community
  • Contributors to Astropy

    Astropy has organically grown from the mailing list

    Astropy has over 90 contributors from around the world

    Project Coordinators

    • Perry Greenfield

    • Thomas Robitaille

    • Erik Tollerud

    Astropy Core


    Only has Numpy as a required dependency (easy to install)

    Well tested, documented, and stable code

    Works on Linux, MacOS X, and Windows

    Python 2 and 3 compatible

    Latest stable release v0.4.2 on Sept 23

    Core data structures and transformations

  • Constants
  • Units and Quantities
  • N-dimensional datasets
  • Data Tables
  • Time and Dates
  • Astronomical Coordinate Systems
  • World Coordinate System
  • Models and Fitting

  • Connecting up: Files and I/O

  • Unified file read/write interface
  • FITS File handling
  • ASCII Tables
  • VOTable XML handling
  • Miscellaneous Input/Output

  • Astronomy computations and utilities

  • Convolution and filtering
  • Cosmological Calculations
  • Astrostatistics Tools
  • Virtual Observatory Access

  • Analysis with Units

    In [5]:
    from astropy import constants as c
    $6.67384\times 10^{-11} \; \mathrm{\frac{m^{3}}{kg\,s^{2}}}$
    In [6]:
    M = c.M_earth
    $5.9742\times 10^{+24} \; \mathrm{kg}$
    In [7]:
    from astropy import units as u
    r = c.R_earth
    v_esc = (2 * c.G * M / r)**0.5
    $11.1814 \; \mathrm{\frac{km}{s}}$
    In [8]:
    v_esc = ((2 * c.G * M / (r+559***0.5)
    $10.7214 \; \mathrm{\frac{km}{s}}$
    In [9]:
    v_esc = ((2 * c.G * 3 * u.m / (r+559***0.5)
    UnitsError                                Traceback (most recent call last)
    <ipython-input-9-871ca449b6fa> in <module>()
          1 v_esc = ((2 * c.G * 3 * u.m / (r+559***0.5)
    ----> 2
    /Users/crawford/programs/astropy/astropy/units/quantity.pyc in to(self, unit, equivalencies)
        586         unit = Unit(unit)
        587         new_val = np.asarray(
    --> 588   , self.value, equivalencies=equivalencies))
        589         return self._new_view(new_val, unit)
    /Users/crawford/programs/astropy/astropy/units/core.pyc in to(self, other, value, equivalencies)
        924             If units are inconsistent
        925         """
    --> 926         return self.get_converter(other, equivalencies=equivalencies)(value)
        928     def in_units(self, other, value=1.0, equivalencies=[]):
    /Users/crawford/programs/astropy/astropy/units/core.pyc in get_converter(self, other, equivalencies)
        860         except UnitsError:
        861             return self._apply_equivalences(
    --> 862                 self, other, self._normalize_equivalencies(equivalencies))
        863         return lambda val: scale * _condition_arg(val)
    /Users/crawford/programs/astropy/astropy/units/core.pyc in _apply_equivalences(self, unit, other, equivalencies)
        823         raise UnitsError(
        824             "{0} and {1} are not convertible".format(
    --> 825                 unit_str, other_str))
        827     def get_converter(self, other, equivalencies=[]):
    UnitsError: 'm(3/2) / (kg(1/2) s)' and 'km / s' (speed) are not convertible

    Using Coordinates

    In []:
    from astropy import units as u
    from astropy.coordinates import SkyCoord
    c1 = SkyCoord('00h42m00s', '+41d12m00s', 'icrs')
    In []:
    print("{0} {1}".format( c1.ra,c1.dec))
    In []:
    print c1.to_string('hmsdms')
    In []:
    c2 = SkyCoord(ra=11*, dec=10*, distance=11.5*u.pc, frame='icrs')

    Also available are coordinate transformation between different systems (e.g. ICRS, FK5, galactic) and matching catalags of coordinates.


    Astropy also has a modelling fitting package. Let's see how it works. Let's create a Gaussian shape and add some noise to it.

    In []:
    import numpy as np
    x = np.linspace(-5., 5., 200)
    y = 3 * np.exp(-0.5 * (x - 1.3)**2 / 0.8**2)
    y += np.random.normal(0., 0.2, x.shape)

    Now let's fit the model using the astropy modeling class

    In []:
    from astropy.modeling import models, fitting
    g_init = models.Gaussian1D(amplitude=1., mean=0, stddev=1.)
    fit_g = fitting.LevMarLSQFitter()
    g = fit_g(g_init, x, y)
    In []:
    import pylab as plt
    plt.plot(x, y, 'ko')
    plt.plot(x, g(x), 'r-', lw=2, label='Gaussian')

    A range of different models already exist for 1-D and 2-D fitting. The API for the modeling class is still being refined but it should be stable in the next major release.

    In addition to what has been shown so far, a number of core data structures and transformations have been included here to help build and coordinate other packages. These include:
    • Quantity: An object with a value and unit
    • Table: functionality for storing and manipulating heterogeneous tables of data
    • NDData: A general astronomical data object including data, meta, uncertainty, wcs
    • Time: functionality for manipulating astronomical relevant times and dates
    • WCS: World Coordinate Systems

    Accessing Data

  • Tools for accessing the virtual observatory

  • In []:
    from astropy.vo.client import conesearch
  • Tools for reading/writing FITS files (formerly pyfits)

  • In []:
    from import fits
  • Tools for reading in ascii tables including CDS, IPAC, HTML, Latex, Sextractor

  • In []:
    from import ascii
    table ="", 
    In []:
    print table

    Cosmology in Astropy

    In []:
    from astropy.cosmology import WMAP9 as cosmo
    In []:

    A number of cosmological models are already available and the user can define their own cosmological models including dark energy and neutrino properties

    In []:
    from astropy.cosmology import WMAP7 
    from astropy.cosmology import WMAP9 as cosmo
    from astropy.cosmology import Planck13 
    z = np.linspace(0,10,200)
    plt.plot(z, WMAP7.luminosity_distance(z)-cosmo.luminosity_distance(z), 'b-', label='WMAP7')
    plt.plot(z, cosmo.luminosity_distance(z)-cosmo.luminosity_distance(z), '-', color='black', label='WMAP9')
    plt.plot(z, Planck13.luminosity_distance(z)-cosmo.luminosity_distance(z), 'g-', label='Planck13')
    plt.ylabel('$\Delta D_L [%s]$' % cosmo.luminosity_distance(0).unit)

    Useful statistics for Astronomy

    In []:
    from astropy import stats
    for x in stats.funcs.__all__: print x

    Astropy Framework

    Development of testing, documentation, and installation infrastructre to make it easier to build and deploy your own code

    Package Template

    Astropy Affiliated Packages

    Astropy Affiliated Packages

    These packages are at different stages of development and there are a number of other packages in early development which are not mentioned here. Some of the packages will be integrated into the core astropy package.


    In []:
    import aplpy
    gc = aplpy.FITSFigure('2MASS_k.fits')


    In []:
    from astroquery.simbad import Simbad
    result_table = Simbad.query_object("m1")

    Services available to query include Vizier, Simbad, NED, SDSS, GAMA, archives, catalogs, and many more online resources


    In []:
    import ccdproc
    ccd ='a8280418.fits', unit=u.adu)
    In []:
    ccd = ccdproc.subtract_overscan(ccd, fits_section=ccd.header['biassec'], 
                                    median=True, model=models.Polynomial1D(5))
    ccd = ccdproc.trim_image(ccd, fits_section=ccd.header['trimsec'])
    ccd = ccdproc.create_deviation(ccd, readnoise=ccd.header['rdnoise']*u.electron, 
    ccd.write('out.fits', clobber=True)
    In []:
    from astropy import log
    In []:
    fc = aplpy.FITSFigure(

    How to get involved

    Download and install astropy


    Provide feedback (submit issues, ask questions)

    Use the astropy template and astropy classes for your packages

    Look for 'easy' issues and submit a pull request

    Contribute code either to astropy or an affiliated package

    Astropy Resources

    Twitter: @astropy
    General Mailing List:
    Mailing list for developers:

    This talk made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration, 2013).

    Special thank you to Thomas Robitaille, Adrian Price-Whelan, Mathew Craig, and the Astropy Community for material for this talk.