.. _gtpsf: http://fermi.gsfc.nasa.gov/ssc/data/analysis/scitools/help/gtpsf.txt
.. _gtselect: http://fermi.gsfc.nasa.gov/ssc/data/analysis/scitools/help/gtselect.txt
.. _gtmktime: https://www.slac.stanford.edu/exp/glast/wb/prod/pages/sciTools_gtmktime/gtmktime_help.htm
.. _ctselect: http://cta.irap.omp.eu/ctools/doc/ctselect.html
.. _IAU SOFA: http://www.iausofa.org/
.. _SOFA Time Scale and Calendar Tools: http://www.iausofa.org/2015_0209_C/sofa/sofa_ts_c.pdf
.. _Time in Fermi data analysis: http://fermi.gsfc.nasa.gov/ssc/data/analysis/documentation/Cicerone/Cicerone_Data/Time_in_ScienceTools.html
.. _Times in Gammalib: http://cta.irap.omp.eu/gammalib-devel/user_manual/modules/obs.html#times-in-gammalib
.. _xTime: https://heasarc.gsfc.nasa.gov/cgi-bin/Tools/xTime/xTime.pl
.. _Astropy time: http://docs.astropy.org/en/latest/time/index.html
.. _ISO 8601: https://en.wikipedia.org/wiki/ISO_8601
.. _2015A%26A...574A..36R: http://adsabs.harvard.edu/abs/2015A%26A...574A..36R
.. _Sherpa: http://cxc.harvard.edu/sherpa/
.. _SESAME: http://cds.u-strasbg.fr/cgi-bin/Sesame
.. _HFWG Recommendation R3: https://heasarc.gsfc.nasa.gov/docs/heasarc/ofwg/docs/ofwg_recomm/r3.html
.. _OGIP HDUCLAS recommendation: https://heasarc.gsfc.nasa.gov/docs/heasarc/ofwg/docs/ofwg_recomm/hduclas.html
.. _OGIP event list: https://heasarc.gsfc.nasa.gov/docs/heasarc/ofwg/docs/events/ogip_94_003/ogip_94_003.html
.. _OGIP GTI: http://heasarc.gsfc.nasa.gov/docs/heasarc/ofwg/docs/rates/ogip_93_003/ogip_93_003.html#tth_sEc6.3
.. _OGIP effective area: https://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/memos/cal_gen_92_019/cal_gen_92_019.html
.. _OGIP energy grid: http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/memos/cal_gen_92_003/cal_gen_92_003.html#tth_sEc7
.. _OGIP radial PSF: http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/docs/memos/cal_gen_92_020/cal_gen_92_020.html
.. _restructured text (RST): http://sphinx-doc.org/rest.html
.. _Sphinx: http://sphinx-doc.org/index.html
.. _Readthedocs: https://readthedocs.org
.. _Sphinx RTD theme FAQ entry: http://docs.readthedocs.io/en/latest/faq.html#i-want-to-use-the-read-the-docs-theme-locally
.. _WCSLIB: http://www.atnf.csiro.au/people/mcalabre/WCS/
.. _FITS standard: https://fits.gsfc.nasa.gov/standard40/fits_standard40aa-le.pdf
.. _FITS WCS: http://fits.gsfc.nasa.gov/fits_wcs.html
.. _FITS time paper: http://adsabs.harvard.edu/abs/2015A%26A...574A..36R
.. _Dictionary of Commonly Used FITS Keywords: https://heasarc.gsfc.nasa.gov/docs/fcg/common_dict.html
.. _equatorial coordinate system: https://en.wikipedia.org/wiki/Equatorial_coordinate_system
.. _Wikipedia - ICRS: https://en.wikipedia.org/wiki/International_Celestial_Reference_System
.. _Galactic coordinate system: https://en.wikipedia.org/wiki/Galactic_coordinate_system
.. _epoch: https://en.wikipedia.org/wiki/Epoch_(astronomy)
.. _equinox: https://en.wikipedia.org/wiki/Equinox_(celestial_coordinates)
.. _horizontal coordinate system: https://en.wikipedia.org/wiki/Horizontal_coordinate_system
.. _zenith: https://en.wikipedia.org/wiki/Zenith
.. _1995A%26AS..113..159C: http://adsabs.harvard.edu/abs/1995A%26AS..113..159C
.. _Wikipedia - PSF: https://en.wikipedia.org/wiki/Point_spread_function
.. _2013ApJ...765...54A: http://adsabs.harvard.edu/abs/2013ApJ...765...54A
.. _2013PASP..125..719H: http://adsabs.harvard.edu/abs/2013PASP..125..719H
.. _2016JCAP...02..039M: http://adsabs.harvard.edu/abs/2016JCAP...02..039M
.. _2015PhRvD..91j2001B: http://adsabs.harvard.edu/abs/2015PhRvD..91j2001B
.. _2014PhRvD..89d2001A: http://adsabs.harvard.edu/abs/2014PhRvD..89d2001A
.. _2015PhRvL.115w1301A: http://adsabs.harvard.edu/abs/2015PhRvL.115w1301A
.. _2016PhRvD..93f2004C: http://adsabs.harvard.edu/abs/2016PhRvD..93f2004C
.. _LAT_edisp_usage: http://fermi.gsfc.nasa.gov/ssc/data/analysis/documentation/Pass8_edisp_usage.html
.. _HEALPix algorithm: http://healpix.jpl.nasa.gov/
.. _astropy.coordinates: http://astropy.readthedocs.io/en/latest/coordinates/index.html
.. _see also section for astropy.coordinates: http://astropy.readthedocs.io/en/latest/coordinates/index.html#see-also
.. _astropy.coordinates.SkyCoord: http://astropy.readthedocs.io/en/latest/api/astropy.coordinates.SkyCoord.html
.. _astropy.coordinates.AstrometricFrame: http://astropy.readthedocs.io/en/latest/api/astropy.coordinates.AstrometricFrame.html
.. _astropy.coordinates.AltAz: http://astropy.readthedocs.io/en/latest/api/astropy.coordinates.AltAz.html
.. _Astropy astrometric frames: http://astropy.readthedocs.io/en/latest/coordinates/matchsep.html#astropy-astrometric-frames
.. _PyGamma15 workshop: http://gammapy.github.io/PyGamma15/
.. _meeting in April 2016 in Meudon: https://github.com/open-gamma-ray-astro/2016-04_IACT_DL3_Meeting
.. _meeting in March 2017 in Heidelberg: https://github.com/open-gamma-ray-astro/2017-03_IACT_DL3_Meeting
.. _Gammapy: http://gammapy.org/
.. _ctools: http://cta.irap.omp.eu/ctools/
.. _gamma-cat: https://gamma-cat.readthedocs.io/
.. _Explanatory Supplement to the Astronomical Almanac: https://ui.adsabs.harvard.edu/abs/2014AAS...22324720U
