pythonpyephem

look up planet or moon by name in pyephem?

I'm writing a little pyephem program where the user passes in the name of a planet or moon, and then the program does some calculations about it. I couldn't find how to look up a planet or moon by name, like you can with stars (ephem.star('Arcturus')), so my program currently has a lookup table for planet and moon names. Can pyephem do this? If not, would it be worth adding?

Solution

  • An interesting question! There does exist an internal method that the underlying _libastro uses to tell ephem itself what objects are supported:

    import ephem
from pprint import pprint
pprint(ephem._libastro.builtin_planets())

    Which prints:

    [(0, 'Planet', 'Mercury'),
 (1, 'Planet', 'Venus'),
 (2, 'Planet', 'Mars'),
 (3, 'Planet', 'Jupiter'),
 (4, 'Planet', 'Saturn'),
 (5, 'Planet', 'Uranus'),
 (6, 'Planet', 'Neptune'),
 (7, 'Planet', 'Pluto'),
 (8, 'Planet', 'Sun'),
 (9, 'Planet', 'Moon'),
 (10, 'PlanetMoon', 'Phobos'),
 (11, 'PlanetMoon', 'Deimos'),
 (12, 'PlanetMoon', 'Io'),
 (13, 'PlanetMoon', 'Europa'),
 (14, 'PlanetMoon', 'Ganymede'),
 (15, 'PlanetMoon', 'Callisto'),
 (16, 'PlanetMoon', 'Mimas'),
 (17, 'PlanetMoon', 'Enceladus'),
 (18, 'PlanetMoon', 'Tethys'),
 (19, 'PlanetMoon', 'Dione'),
 (20, 'PlanetMoon', 'Rhea'),
 (21, 'PlanetMoon', 'Titan'),
 (22, 'PlanetMoon', 'Hyperion'),
 (23, 'PlanetMoon', 'Iapetus'),
 (24, 'PlanetMoon', 'Ariel'),
 (25, 'PlanetMoon', 'Umbriel'),
 (26, 'PlanetMoon', 'Titania'),
 (27, 'PlanetMoon', 'Oberon'),
 (28, 'PlanetMoon', 'Miranda')]

    You only need the last of these three items, so you could build a list of names like:

    >>> pprint([name for _0, _1, name in ephem._libastro.builtin_planets()])

    which returns:

    ['Mercury',
 'Venus',
 'Mars',
 'Jupiter',
 'Saturn',
 'Uranus',
 'Neptune',
 'Pluto',
 'Sun',
 'Moon',
 'Phobos',
 'Deimos',
 'Io',
 'Europa',
 'Ganymede',
 'Callisto',
 'Mimas',
 'Enceladus',
 'Tethys',
 'Dione',
 'Rhea',
 'Titan',
 'Hyperion',
 'Iapetus',
 'Ariel',
 'Umbriel',
 'Titania',
 'Oberon',
 'Miranda']

    You could then grab any of these objects, given its name, with a simple getattr(ephem, name) call.