minor planet checking
Perform checks for the presence of minor bodies at astronomical locations for a given epoch.
pip install pympc
or download/clone source and:
python setup.py install
First we need to import the package and grab the orbit element catalogue. This must be done at least once prior to any searches and can be run to overwrite the catalogues with the latest versions. The default call signature is shown.
import pympc xephem_cat =pympc.update_catalogue() print(xephem_cat) # e.g. /tmp/mpcorb_xephem.csv
The catalogue downloaded will be the
from the Minor Planet Center.
The Near Earth Asteroid and Comets catalogues will be downloaded and used to update the
mpcorb entries based on
the values of the
include_comets arguments (both default to
It will create a csv file for each catalogue downloaded in the
xephem database format and return
the filepath to this file. By default the file will be saved in the user's temporary directory - this can
be changed by setting the
Having downloaded the catalogue (see Setup), we can now search for minor bodies at a given location.
Within an interpretor session, define a search location, epoch and radius and run the search.
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 = 5 * u.arcmin observatory = 950 # observatory code for La Palma pympc.minor_planet_check(ra, dec, epoch, search_radius, observatory=observatory)
Results are returned as an astropy table.
The above example uses explicit quantities, but if passed simple float arguments, and the program will assume the
units (see comments below and
pympc.minor_planet_check() docstring for unit assumptions).
ra = 230.028 # assumed degrees dec = -11.774 # assumed degrees epoch = 58484. # assumed MJD search_radius = 30 # assumed arcseconds observatory = 950 # observatory code for La Palma pympc.minor_planet_check(ra, dec, epoch, search_radius, observatory=observatory)
By default, the search will use a default filepath for the catalogue. if the file has been moved - or a
cat_dir was passed to
pympc.update_catalogue() - then the filepath can be specified.
pympc.minor_planet_check(ra, dec, epoch, search_radius, xephem_filepath='/path/to/mpcorb_xphem.csv', observatory=observatory)
Defining an observer
By default, if the
observatory argument is not passed, the program will return geocentric coordinates. However, for
relatively nearby objects like minor bodies, there can be signicant parallax introduced by the location of an observer
on the Earth's surface. For this reason it is crucial to pass either an
observatory code or a tuple containing the observatory
information. See the documentation for
pympc.minor_planet_check() for more details.
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 directly, to avoid the overhead associated with converting input arguments in
if you provide them directly as required (see
_minor_planet_check() docstring). Note that in this case a list of
tuples is returned, rather than an astropy table.
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)
Console script searching
Installation of the package will create a
minor_planet_check script, which can be accessed
from the command line. The options follow the same as the interactive searching, and results
are displayed as a table. For help on the command line use:
It is not currently possible to pass a custom set of observatory coordinates to the script - an existing observatory code must be passed.
The orbits are propagated following xephem (via the pyephem package), and this does not account for perturbations of the orbits. Thus, the accuracy of the position is dependent on the time difference between the epoch of the orbit elements and the epoch at which the search is being performed. Epoch differences between orbital elements calculation and observation of around a month or two are fine for typical positional accuracies of less than a few arcsecond for the vast majority of minor bodies. Note, however, that a small number of bodies (those undergoing strong perturbations and close to Earth) maybe quite inaccurate (arcminutes). A fuller analysis is given in notebooks/positional_accuracy.ipynb.
xephem package can only provide geocentric astrometric positions.
pympc will calculate the topocentric
correction as a post-processing to the initial position. The simple geometric correction applied is more than sufficient
for the overwhelming majority of minor bodies, but for some near earth objects the correction can be large and the
relatively simple treatment by
pympc may not be sufficient. Additionally, in order to find matches in geocentric
positions prior to applying the topocentric correction, a buffer is added to the search radius - this should capture
the vast majority of cases where the geocentric position is outside the seach radius but the topocentric position is
within it - although no guarantees. To work around this you can artifically inflate your search radius and filter
The filtering of matches based on magnitude via
max_mag argument to
minor_planet_check() 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
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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