.. note::
    :class: sphx-glr-download-link-note

    Click :ref:`here <sphx_glr_download_generated_examples_io_fits-tables.py>` to download the full example code
.. rst-class:: sphx-glr-example-title

.. _sphx_glr_generated_examples_io_fits-tables.py:


=====================================================================
Accessing data stored as a table in a multi-extension FITS (MEF) file
=====================================================================

FITS files can often contain large amount of multi-dimensional data and
tables. This example opens a FITS file with information
from Chandra's HETG-S instrument.

The example uses `astropy.utils.data` to download multi-extension FITS (MEF)
file, `astropy.io.fits` to investigate the header, and
`astropy.table.Table` to explore the data.

-------------------

*By: Lia Corrales, Adrian Price-Whelan, and Kelle Cruz*

*License: BSD*

-------------------



Use `astropy.utils.data` subpackage to download the FITS file used in this
example. Also import `~astropy.table.Table` from the `astropy.table` subpackage
and `astropy.io.fits`



.. code-block:: python


    from astropy.utils.data import get_pkg_data_filename
    from astropy.table import Table
    from astropy.io import fits







Download a FITS file



.. code-block:: python


    event_filename = get_pkg_data_filename('tutorials/FITS-tables/chandra_events.fits')







Display information about the contents of the FITS file.



.. code-block:: python


    fits.info(event_filename)





.. rst-class:: sphx-glr-script-out

 Out:

 .. code-block:: none

    Filename: /home/docs/.astropy/cache/download/py3/26e9900d731d08997d99ada3973f4592
    No.    Name      Ver    Type      Cards   Dimensions   Format
      0  PRIMARY       1 PrimaryHDU      30   ()      
      1  EVENTS        1 BinTableHDU    890   483964R x 19C   [1D, 1I, 1I, 1J, 1I, 1I, 1I, 1I, 1E, 1E, 1E, 1E, 1J, 1J, 1E, 1J, 1I, 1I, 32X]   
      2  GTI           3 BinTableHDU     28   1R x 2C   [1D, 1D]   
      3  GTI           2 BinTableHDU     28   1R x 2C   [1D, 1D]   
      4  GTI           1 BinTableHDU     28   1R x 2C   [1D, 1D]   
      5  GTI           0 BinTableHDU     28   1R x 2C   [1D, 1D]   
      6  GTI           6 BinTableHDU     28   1R x 2C   [1D, 1D]


Extension 1, EVENTS, is a Table that contains information about each X-ray
photon that hit Chandra's HETG-S detector.

Use `~astropy.table.Table` to read the table



.. code-block:: python


    events = Table.read(event_filename, hdu=1)







Print the column names of the Events Table.



.. code-block:: python


    print(events.columns)





.. rst-class:: sphx-glr-script-out

 Out:

 .. code-block:: none

    <TableColumns names=('time','ccd_id','node_id','expno','chipx','chipy','tdetx','tdety','detx','dety','x','y','pha','pha_ro','energy','pi','fltgrade','grade','status')>


If a column contains unit information, it will have an associated
`astropy.units` object.



.. code-block:: python


    print(events['energy'].unit)





.. rst-class:: sphx-glr-script-out

 Out:

 .. code-block:: none

    eV


Print the data stored in the Energy column.



.. code-block:: python


    print(events['energy'])




.. rst-class:: sphx-glr-script-out

 Out:

 .. code-block:: none

    energy 
        eV   
    ---------
    13874.715
    2621.1938
    12119.018
    3253.0364
    14214.382
    1952.7239
    3267.5334
    3817.0366
    2252.7295
    6154.1094
          ...
    4819.8286
    12536.866
    2599.5652
    15535.768
    6653.0815
    14362.482
    14653.954
     6652.827
     9672.882
    1875.9359
    Length = 483964 rows


**Total running time of the script:** ( 0 minutes  3.404 seconds)


.. _sphx_glr_download_generated_examples_io_fits-tables.py:


.. only :: html

 .. container:: sphx-glr-footer
    :class: sphx-glr-footer-example



  .. container:: sphx-glr-download

     :download:`Download Python source code: fits-tables.py <fits-tables.py>`



  .. container:: sphx-glr-download

     :download:`Download Jupyter notebook: fits-tables.ipynb <fits-tables.ipynb>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.readthedocs.io>`_