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minor planet checking

Project description

pympc

perform checks for the presence of minor bodies at astronomical locations for a given epoch.

installation

pip install pympc

or download source and:

python setup.py install

examples

define where we want the orbit catalogue to be downloaded to (see next section)

$ export MPCORB_JSON_PATH = /my/file/path/mpcorb_extended.json

import the package and (optionally) grab the catalogue - this must be done at least once prior to doing any searches and can be run to overwrite the catalogue with the latest version from the Minor Planet Center

>>> import pympc
>>> pympc.update_catalogue()

Note by default it will also download the Near Earth Asteroid catalogue and use orbits from that catalogue where overlap exists with the main MPCORB catalogue, since they are more regularly updated and subject to larger perturbations. This can be switched off with pympc.update_catalogue(include_nea=False)

example 1

define our search location, epoch and radius and run the check

>>> import astropy.units as u
>>> from astropy.time import Time
>>> ra = 230.028 * u.deg
>>> dec = -11.774 * u.deg
>>> epoch = Time("2019-01-01T00:00")
>>> search_radius = 0.5 * u.arcmin
>>> max_mag = 20
>>> pympc.minor_planet_check(ra, dec, epoch, search_radius, max_mag)
example 2

here we use float arguments, and the program assumes the units (see pympc.minor_planet_check() docstring)

>>> ra = 230.028  # assumed degrees
>>> dec = -11.774  # assumed degrees
>>> epoch = 58484.  # assumed MJD
>>> search_radius = 30  # assumed arcseconds
>>> max_mag = 20
>>> pympc.minor_planet_check(ra, dec, epoch, search_radius, max_mag)

setting the orbit catalogue location

the location to download the MPCORB catalogue is set via the environment variable MPCORB_JSON_PATH (e.g. export MPCORB_JSON_PATH = /my/file/path/mpcorb.json). If this is not found the catalogue will download to the default location of /tmp/mpcorb_extended.json.

speed and multiprocessing

the check should take of order a second or two, depending on multiprocessing capabilities.

the private function which actually performs the calculation is _minor_planet_check() (note leading underscore). this can be called to avoid the overhead associated with converting input arguments to minor_planet_check(), if you can provide them directly as required (see _minor_planet_check() docstring).

by default the program will calculate positions of bodies in the catalogue multiprocessed. to switch this off set chunk_size = 0, i.e.:

>>> pympc.minor_planet_check(ra, dec, epoch, search_radius, chunk_size=0)

limitations

the orbits are propagated by xephem, and that package does not account for perturbations of the orbits. thus the accuracy of the position is dependant on the time difference between the epoch of the orbit elements and the epoch at which the search is being performed. epoch differences of around a month or less should be fine for typical positional accuracies of ground-based observations (~arcsecond), but time differences of several months can accrue to inaccuracies of around ~arcminute for certain bodies.

currently the epoch of the orbit elements is visible in the xephem db strings returned by minor_planet_check() as a decimal year format (e.g. ..,2019.317808,..). some diagnostic information and warning when using large time differences is to be implemented.

the filtering of matches based on magnitude via max_mag is limited by the accuracy of the magnitude information in the database so some buffer should be applied to the desired magnitude cutoff to allow for this.

acknowledgments

this package makes use of data and/or services provided by the International Astronomical Union's Minor Planet Center.

orbit elements are also sourced from Lowell Observatory, which is funded by the Lowell Observatory Endowment and NASA PDART grant NNX16AG52G.

based from a package developed by Chris Klein and Duncan Galloway.

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