Oct 31, 2013

Have fun tracking Comet ISON with PyEphem

I'm not an astronomer, but since I was 10 I've had enough curiosity to let me look at night skies and practice the base notions of amateur astronomy. 2013 is a lucky year for comet observations, C/2011 L4 (PANSTARRS), C/2012 F6 (Lemmon) for example and currently transiting C/2012 S1 (ISON).

PyEphem "provides scientific-grade astronomical computations for the Python programming language" and it uses Xephem routines.

Not all sky bodies can be natively computed by PyEphem. A comet must be loaded from external catalog definitions of orbital parameters. PyEphem documentation provides links to various catalogs.

gianluca:~$ mkvirtualenv astropy --no-site-packages
New python executable in astropy/bin/python
Installing setuptools............done.
Installing pip...............done.
gianluca:~$ workon astropy
(astropy)gianluca:~$ pip install ephem
Downloading/unpacking pyephem
  Downloading pyephem-3.7.5.1.tar.gz (703kB): 703kB downloaded
  Running setup.py egg_info for package pyephem

Installing collected packages: pyephem
  Running setup.py install for pyephem
    building 'ephem._libastro' extension
    gcc -pthread -fno-strict-aliasing -DNDEBUG -g -fwrapv -O2 -Wall -Wstrict-prototypes -fPIC -Ilibastro-3.7.5 -I/usr/include/python2.7 -c extensions/_libastro.c -o build/temp.linux-x86_64-2.7/extensions/_libastro.o
...
...
...
Successfully installed pyephem
Cleaning up...
(astropy)gianluca:~$

After installing virtualenv and virtualenvwrapper I created a virtualenv called astropy and installed PyEphem therein, a simple script shows how fun(and powerful) is to use the PyEphem library.

import ephem

# load Comet ISON object from catalog http://www.minorplanetcenter.net/iau/Ephemerides/Comets/Soft03Cmt.txt
ison = ephem.readdb("C/2012 S1 (ISON),h,11/28.7747/2013,62.3990,295.6529,345.5644,1.000002,0.012444,2000,7.5,3.2")
date = '2013/10/31'

# compute on date
ison.compute(date)

# define an observer
Rome = ephem.city('Rome')
rome_watcher = ephem.Observer()
rome_watcher.lat = Rome.lat
rome_watcher.lon = Rome.lon
rome_watcher.date = date

# print some useful data computed on the loaded body
print("Tracking object: %s on date: %s from: %s" % (ison.name, date, Rome.name))
print "%s is in constellation: %s with magnitude %s" % (ison.name, ephem.constellation(ison)[1], ison.mag)
print("Rome next rising: %s" % rome_watcher.next_rising(ison))
print("Rome next setting: %s" % rome_watcher.next_setting(ison))
print("Earth distance: %s AUs" % ison.earth_distance)
print("Sun distance: %s AUs" % ison.sun_distance)

Output:

(astropy)gianluca:~$ python tracking_comet_ison.py 
Tracking object: C/2012 S1 (ISON) on date: 2013/10/31 from: Rome
C/2012 S1 (ISON) is in constellation: Leo with magnitude 8.07
Rome next rising: 2013/10/31 01:12:31
Rome next setting: 2013/10/31 14:07:39
Earth distance: 1.24149298668 AUs
Sun distance: 1.00681865215 AUs

Clear skies to all :) and have fun!

Moon at -62:38:12.8, 15:31:15.0 observing from Rome, IT

Have fun tracking Comet ISON with PyEphem

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