Friday, July 31, 2020

Python 3.8.5 : PyEphem astronomy library for Python - part 001.

About this python package, you can find it from the official website.
PyEphem provides an ephem Python package for performing high-precision astronomy computations. The underlying numeric routines are coded in C and are the same ones that drive the popular XEphem astronomy application, whose author, Elwood Charles Downey, generously gave permission for their use in PyEphem. The name ephem is short for the word ephemeris, which is the traditional term for a table giving the position of a planet, asteroid, or comet for a series of dates.
Because I like astronomy and lately a lot has happened in this field, I thought I would come up with some simple tutorials for those who are interested.
This tutorial is tested on a Linux distribution called Fedora 32 with Python version 3.8.5.
I installed this python packet with the pip3 tool.
[mythcat@desk ~]$ sudo pip3 install ephem --user
WARNING: Running pip install with root privileges is generally not a good idea. 
Try `pip3 install --user` instead.
Collecting ephem
...
Installing collected packages: ephem
Successfully installed ephem-3.7.7.1
You know that NASA has launched the Mars Perseverance rover, so let's play with this topic a bit.
Let's see current azimuth and elevation for planet Mars.
For this is need the position of the observer and then is compute the position of the planet Mars.
I used the position of the Greenwich for the observer, but you can create your oun observer and use it.
[mythcat@desk ~]$ python3
Python 3.8.5 (default, Jul 20 2020, 00:00:00) 
[GCC 10.1.1 20200507 (Red Hat 10.1.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import ephem
>>> import math
>>> convert = math.pi / 180.
>>> mars = ephem.Mars()
>>> greenwich = ephem.Observer()
>>> greenwich.lat = "51.477928"
>>> greenwich.lon = "-0.001545"
>>> mars.compute(greenwich)
>>> az_deg, alt_deg = mars.az*convert, mars.alt*convert
>>> print(f"Mars' current azimuth and elevation: {az_deg:.2f} {alt_deg:.2f}")
Mars' current azimuth and elevation: 0.11 -0.01
Let's see another example with Mars to take ascension and declination for the epoch specified:
...
>>> import datetime
>>> now = datetime.datetime.now()
>>> print(now)
2020-07-31 19:11:42.312027
>>> mars.compute(now)
>>> print(mars.ra)
1:12:43.64
>>> print(mars.dec)
3:33:22.6
You can get the magnitude, size (diameter in arcseconds) and size (radius as an angle):
>>> print(mars.mag)
-1.11
>>> print(mars.size)
14.555475234985352
>>> print(mars.radius)
0:00:07.3
You can easily see which constellation Mars is on.
>>> ephem.constellation(mars)
('Psc', 'Pisces')

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