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# -*- coding: utf-8 -*-
"""
===================================================================
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 <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:
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
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:
m33 = SkyCoord(23.4621 * u.deg, 30.6599417 * u.deg)
##############################################################################
# Use `astropy.coordinates.EarthLocation` to provide the location of Bear
# Mountain and set the time to 11pm EDT on 2012 July 12:
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.
m33altaz = m33.transform_to(AltAz(obstime=time,location=bear_mountain))
print("M33's Altitude = {0.alt:.2}".format(m33altaz))
##############################################################################
# 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:
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:
m33airmasss_July13night = m33altazs_July13night.secz
##############################################################################
# Plot the airmass as a function of time:
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()
##############################################################################
# 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:
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.
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:
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:
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.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()
|
