.. _sphx_glr_generated_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 convenient and/or complex observation
planning, consider the `astroplan `_
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.
Import numpy and matplotlib. For the latter, use a nicer set of plot
parameters and set up support for plotting/converting quantities.
.. code-block:: python
import numpy as np
import matplotlib.pyplot as plt
from astropy.visualization import astropy_mpl_style, quantity_support
plt.style.use(astropy_mpl_style)
quantity_support()
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:: /generated/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)
Do the same with `~astropy.coordinates.get_moon` to find when the moon is
up. Be aware that this will need to download a 10MB file from the internet
to get a precise location of the moon.
.. code-block:: python
from astropy.coordinates import get_moon
moon_July12_to_13 = get_moon(times_July12_to_13)
moonaltazs_July12_to_13 = moon_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 beautiful 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.plot(delta_midnight, moonaltazs_July12_to_13.alt, color=[0.75]*3, ls='--', label='Moon')
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, 0*u.deg, 90*u.deg,
sunaltazs_July12_to_13.alt < -0*u.deg, color='0.5', zorder=0)
plt.fill_between(delta_midnight, 0*u.deg, 90*u.deg,
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*u.hour, 12*u.hour)
plt.xticks((np.arange(13)*2-12)*u.hour)
plt.ylim(0*u.deg, 90*u.deg)
plt.xlabel('Hours from EDT Midnight')
plt.ylabel('Altitude [deg]')
plt.show()
.. image:: /generated/examples/coordinates/images/sphx_glr_plot_obs-planning_002.png
:align: center
**Total running time of the script:** ( 0 minutes 4.479 seconds)
.. container:: sphx-glr-footer
.. container:: sphx-glr-download
:download:`Download Python source code: plot_obs-planning.py `
.. container:: sphx-glr-download
:download:`Download Jupyter notebook: plot_obs-planning.ipynb `
.. rst-class:: sphx-glr-signature
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