.. _sphx_glr_auto_examples_coordinates_plot_obs-planning.py:


===================================================================
Determining and plotting the altitude/azimuth of a celestial object
===================================================================

This example demonstrates coordinate transformations and the creation of
visibility curves to assist with observing run planning.

In this example, we make a `~astropy.coordinates.SkyCoord` instance for M33.
The altitude-azimuth coordinates are then found using
`astropy.coordinates.EarthLocation` and `astropy.time.Time` objects.

This example is meant to demonstrate the capabilities of the
`astropy.coordinates` package. For more convienent and/or complex observation
planning, consider the `astroplan <https://astroplan.readthedocs.org/>`_
package.

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

*By: Erik Tollerud, Kelle Cruz*

*License: BSD*

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


Let’s suppose you are planning to visit picturesque Bear Mountain State Park
in New York, USA. You’re bringing your telescope with you (of course), and
someone told you M33 is a great target to observe there. You happen to know
you’re free at 11:00 pm local time, and you want to know if it will be up.
Astropy can answer that.

Make print work the same in all versions of Python, set up numpy,
matplotlib, and use a nicer set of plot parameters:


.. code-block:: python


    from __future__ import print_function
    import numpy as np
    import matplotlib.pyplot as plt
    from astropy.visualization import astropy_mpl_style
    plt.style.use(astropy_mpl_style)








Import the packages necessary for finding coordinates and making
coordinate transformations


.. code-block:: python


    import astropy.units as u
    from astropy.time import Time
    from astropy.coordinates import SkyCoord, EarthLocation, AltAz







`astropy.coordinates.SkyCoord.from_name` uses Simbad to resolve object
names and retrieve coordinates.

Get the coordinates of M33:


.. code-block:: python


    m33 = SkyCoord.from_name('M33')







Use `astropy.coordinates.EarthLocation` to provide the location of Bear
Mountain and set the time to 11pm EDT on 2012 July 12:


.. code-block:: python


    bear_mountain = EarthLocation(lat=41.3*u.deg, lon=-74*u.deg, height=390*u.m)
    utcoffset = -4*u.hour  # Eastern Daylight Time
    time = Time('2012-7-12 23:00:00') - utcoffset







`astropy.coordinates.EarthLocation.get_site_names` and
`~astropy.coordinates.EarthLocation.get_site_names` can be used to get
locations of major observatories.

Use `astropy.coordinates` to find the Alt, Az coordinates of M33 at as
observed from Bear Mountain at 11pm on 2012 July 12.


.. code-block:: python


    m33altaz = m33.transform_to(AltAz(obstime=time,location=bear_mountain))
    print("M33's Altitude = {0.alt:.2}".format(m33altaz))





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

 Out::

      M33's Altitude = 0.13 deg


This is helpful since it turns out M33 is barely above the horizon at this
time. It's more informative to find M33's airmass over the course of
the night.

Find the alt,az coordinates of M33 at 100 times evenly spaced between 10pm
and 7am EDT:


.. code-block:: python


    midnight = Time('2012-7-13 00:00:00') - utcoffset
    delta_midnight = np.linspace(-2, 10, 100)*u.hour
    frame_July13night = AltAz(obstime=midnight+delta_midnight,
                              location=bear_mountain)
    m33altazs_July13night = m33.transform_to(frame_July13night)







convert alt, az to airmass with `~astropy.coordinates.AltAz.secz` attribute:


.. code-block:: python


    m33airmasss_July13night = m33altazs_July13night.secz







Plot the airmass as a function of time:


.. code-block:: python


    plt.plot(delta_midnight, m33airmasss_July13night)
    plt.xlim(-2, 10)
    plt.ylim(1, 4)
    plt.xlabel('Hours from EDT Midnight')
    plt.ylabel('Airmass [Sec(z)]')
    plt.show()




.. image:: /auto_examples/coordinates/images/sphx_glr_plot_obs-planning_001.png
    :align: center




Use  `~astropy.coordinates.get_sun` to find the location of the Sun at 1000
evenly spaced times between noon on July 12 and noon on July 13:


.. code-block:: python


    from astropy.coordinates import get_sun
    delta_midnight = np.linspace(-12, 12, 1000)*u.hour
    times_July12_to_13 = midnight + delta_midnight
    frame_July12_to_13 = AltAz(obstime=times_July12_to_13, location=bear_mountain)
    sunaltazs_July12_to_13 = get_sun(times_July12_to_13).transform_to(frame_July12_to_13)







Find the alt,az coordinates of M33 at those same times:


.. code-block:: python


    m33altazs_July12_to_13 = m33.transform_to(frame_July12_to_13)







Make a beatiful figure illustrating nighttime and the altitudes of M33 and
the Sun over that time:


.. code-block:: python


    plt.plot(delta_midnight, sunaltazs_July12_to_13.alt, color='r', label='Sun')
    plt.scatter(delta_midnight, m33altazs_July12_to_13.alt,
                c=m33altazs_July12_to_13.az, label='M33', lw=0, s=8,
                cmap='viridis')
    plt.fill_between(delta_midnight.to('hr').value, 0, 90,
                     sunaltazs_July12_to_13.alt < -0*u.deg, color='0.5', zorder=0)
    plt.fill_between(delta_midnight.to('hr').value, 0, 90,
                     sunaltazs_July12_to_13.alt < -18*u.deg, color='k', zorder=0)
    plt.colorbar().set_label('Azimuth [deg]')
    plt.legend(loc='upper left')
    plt.xlim(-12, 12)
    plt.xticks(np.arange(13)*2 -12)
    plt.ylim(0, 90)
    plt.xlabel('Hours from EDT Midnight')
    plt.ylabel('Altitude [deg]')
    plt.show()



.. image:: /auto_examples/coordinates/images/sphx_glr_plot_obs-planning_002.png
    :align: center




**Total running time of the script:**
(0 minutes 3.476 seconds)



.. container:: sphx-glr-download

    **Download Python source code:** :download:`plot_obs-planning.py <plot_obs-planning.py>`


.. container:: sphx-glr-download

    **Download IPython notebook:** :download:`plot_obs-planning.ipynb <plot_obs-planning.ipynb>`