# Ephem¶

class sbpy.data.Ephem[source]

Class for querying, manipulating, and calculating ephemerides

Methods Summary

 from_horizons(targetids[, id_type, epochs, …]) Load target ephemerides from JPL Horizons using astroquery.jplhorizons.HorizonsClass.ephemerides from_miriade(targetids[, objtype, epochs, …]) Load target ephemerides from IMCCE Miriade using astroquery.imcce.MiriadeClass.get_ephemerides from_mpc(targetids[, epochs, location, …]) Load ephemerides from the Minor Planet Center. from_oo(orbit[, epochs, location, scope, …]) Uses pyoorb to derive ephemerides from an Orbit object.

Methods Documentation

classmethod from_horizons(targetids, id_type='smallbody', epochs=None, location='500', **kwargs)[source]

Load target ephemerides from JPL Horizons using astroquery.jplhorizons.HorizonsClass.ephemerides

Parameters
targetidsstr or iterable of str

Target identifier, i.e., a number, name, designation, or JPL Horizons record number, for one or more targets.

id_typestr, optional

The nature of targetids provided; possible values are 'smallbody' (asteroid or comet), 'majorbody' (planet or satellite), 'designation' (asteroid or comet designation), 'name' (asteroid or comet name), 'asteroid_name', 'comet_name', 'id' (Horizons id). Default: 'smallbody'

epochsTime object, or dictionary, optional

Epochs of elements to be queried; Time objects support single and multiple epochs; a dictionary including keywords start and stop, as well as either step or number, can be used to generate a range of epochs. start and stop have to be Time objects (see Epochs and the use of astropy.time). If step is provided, a range of epochs will be queries starting at start and ending at stop in steps of step; step has to be provided as a Quantity object with integer value and a unit of either minutes, hours, days, or years. If number is provided as an integer, the interval defined by start and stop is split into number equidistant intervals. If None is provided, current date and time are used. All epochs should be provided in UTC; if not, they will be converted to UTC and a TimeScaleWarning will be raised. Default: None

locationstr or EarthLocation, optional

Location of the observer using IAU observatory codes (see IAU observatory codes) or as EarthLocation. Default: '500' (geocentric)

**kwargsoptional

Arguments that will be provided to astroquery.jplhorizons.HorizonsClass.ephemerides.

Returns
Ephem object

The resulting object will be populated with columns as defined in ephemerides; refer to that document on information on how to modify the list of queried parameters.

Notes

Examples

>>> from sbpy.data import Ephem
>>> from astropy.time import Time
>>> epoch = Time('2018-05-14', scale='utc')
>>> eph = Ephem.from_horizons('ceres', epochs=epoch)

classmethod from_miriade(targetids, objtype='asteroid', epochs=None, location='500', **kwargs)[source]

Load target ephemerides from IMCCE Miriade using astroquery.imcce.MiriadeClass.get_ephemerides

Parameters
targetidsstr or iterable of str

Target identifier, i.e., a number, name, designation, or JPL Horizons record number, for one or more targets.

objtypestr, optional

The nature of targetids provided; possible values are 'asteroid', 'comet', 'dwarf planet', 'planet', or 'satellite'. Default: 'asteroid'

epochsTime object, or dictionary, optional

Epochs of elements to be queried; Time objects support single and multiple epochs; a dictionary including keywords start and stop, as well as either step or number, can be used to generate a range of epochs. start and stop have to be Time objects (see Epochs and the use of astropy.time). If step is provided, a range of epochs will be queried starting at start and ending at stop in steps of step; step has to be provided as a Quantity object with integer value and a unit of either seconds, minutes, hours, or days. If number is provided as an integer, the interval defined by start and stop is split into number equidistant intervals. If None is provided, current date and time are used. All epochs should be provided in UTC; if not, they will be converted to UTC and a TimeScaleWarning will be raised. Default: None

locationstr or EarthLocation, optional

Location of the observer using IAU observatory codes (see IAU observatory codes) or as EarthLocation. Default: '500' (geocentric)

**kwargsoptional

Arguments that will be provided to astroquery.imcce.MiriadeClass.get_ephemerides.

Returns
Ephem object

The resulting object will be populated with columns as defined in get_ephemerides; refer to that document on information on how to modify the list of queried parameters.

Notes

Examples

>>> from sbpy.data import Ephem
>>> from astropy.time import Time
>>> epoch = Time('2018-05-14', scale='utc')
>>> eph = Ephem.from_horizons('ceres', epochs=epoch)

classmethod from_mpc(targetids, epochs=None, location='500', ra_format=None, dec_format=None, **kwargs)[source]

Load ephemerides from the Minor Planet Center.

Parameters
targetidsstr or iterable of str

Target identifier, resolvable by the Minor Planet Ephemeris Service [MPES], e.g., 2P, C/1995 O1, P/Encke, (1), 3200, Ceres, and packed designations, for one or more targets.

epochsTime object, or dictionary, optional

Request ephemerides at these epochs. May be a single epoch or multiple epochs as Time (see Epochs and the use of astropy.time)or a dictionary describing a linearly-spaced array of epochs. All epochs should be provided in UTC; if not, they will be converted to UTC and a TimeScaleWarning will be raised. If None (default), the current date and time will be used.

For the dictionary format, the keys start (start epoch), step (step size), stop (end epoch), and/or number (number of epochs total) are used. Only one of stop and number may be specified at a time. step, stop, and number are optional. The values of of start and stop must be Time objects. number should be an integer value; step should be a Quantity with an integer value and units of seconds, minutes, hours, or days.

All epochs should be provided in UTC; if not, they will be converted to UTC and a TimeScaleWarning will be raised.

locationvarious, optional

Location of the observer as an IAU observatory code [OBSCODES] (string), a 3-element array of Earth longitude, latitude, altitude, or an EarthLocation. Longitude and latitude should be parseable by Angle, and altitude should be parsable by Quantity (with units of length). If None, then the geocenter (code 500) is used.

ra_formatdict, optional

Format the RA column with to_string using these keyword arguments, e.g., {'sep': ':', 'unit': 'hourangle', 'precision': 1}.

dec_formatdict, optional

Format the Dec column with to_string using these keyword arguments, e.g., {'sep': ':', 'precision': 0}.

**kwargs

Additional keyword arguments are passed to get_ephemerides: eph_type, proper_motion, proper_motion_unit, suppress_daytime, suppress_set, perturbed, unc_links, cache.

Returns
Ephem object

The resulting object will be populated with columns as defined in get_ephemerides; refer to that document on information on how to modify the list of queried parameters.

Notes

• All properties are provided in the J2000.0 reference system.

• See astroquery.mpc.MPC.get_ephemerides and the Minor Planet Ephemeris Service user’s guide [MPES] for details, including acceptable target names.

References

MPES(1,2)

Wiliams, G. The Minor Planet Ephemeris Service. https://minorplanetcenter.net/iau/info/MPES.pdf

OBSCODES

IAU Minor Planet Center. List of observatory codes. https://minorplanetcenter.net/iau/lists/ObsCodesF.html

Examples

Query a single set of ephemerides of Ceres as observed from Maunakea: >>> from sbpy.data import Ephem >>> from astropy.time import Time >>> epoch = Time(‘2018-05-14’, scale=’utc’) >>> eph = Ephem.from_mpc(‘ceres’, epoch, 568) # doctest: +REMOTE_DATA

Query a range of ephemerides of comet 2P/Encke as observed from Maunakea: >>> epochs = {‘start’: Time(‘2019-01-01’), … ‘step’: 1*u.d, ‘number’: 365} >>> eph = Ephem.from_mpc(‘2P’, epochs, 568) # doctest: +REMOTE_DATA

classmethod from_oo(orbit, epochs=None, location='500', scope='full', dynmodel='N', ephfile='de430')[source]

Uses pyoorb to derive ephemerides from an Orbit object. For a list of output parameters, please read the pyoorb documentation.

Parameters
orbitOrbit object

Can contain any number of orbits, ephemerides will be calculated for each orbit. Required fields are:

• target identifier ('targetname')

• semi-major axis ('a', for Keplerian orbit) or perihelion distance ('q', for cometary orbit), typically in au or or x-component of state vector ('x', for cartesian orbit), typically in au

• eccentricity ('e', for Keplerian or cometary orbit) or y-component of state vector ('y', for cartesian orbit) in au

• inclination ('i', for Keplerian or cometary orbit) in degrees or z-component of state vector ('z', for cartesian orbit) in au

• longitude of the ascending node ('Omega', for Keplerian or cometary orbit) in degrees or x-component of velocity vector ('vx', for cartesian orbit), au/day

• argument of the periapsis ('w', for Keplerian or cometary orbit) in degrees or y-component of velocity vector ('vy', for cartesian orbit) in au/day

• mean anomaly ('M', for Keplerian orbits) in degrees or perihelion epoch ('Tp', for cometary orbits) as astropy Time object or z-component of velocity vector ('vz', for cartesian orbit) in au/day

• epoch ('epoch') as Time

• absolute magnitude ('H') in mag

• photometric phase slope ('G')

epochsTime object, optional

Epochs of elements to be queried; must be a Time object holding a single or multiple epochs (see Epochs and the use of astropy.time). If None is provided, current date and time are used. The same time scale that is used in epochs will be applied to the results. Default: None

locationstr, optional, default '500' (geocentric)

Location of the observer.

scopestr

Scope of data to be determined: 'full' obtains all available properties, 'basic' obtains only a limited amount of data. Default: 'full'

dynmodelstr, optional

The dynamical model to be used in the propagation: 'N' for n-body simulation or '2' for a 2-body simulation. Default: 'N'

ephfilestr, optional

Planet and Lunar ephemeris file version as provided by JPL to be used in the propagation. Default: 'de430'

Returns
Ephem object

Examples

Compute ephemerides for Ceres as seen from the Discovery Channel Telescope for the next 10 days at 1hr intervals:

>>> import numpy as np
>>> from sbpy.data import Orbit, Ephem
>>> from astropy.time import Time
>>> epochs = Time(Time.now().jd + np.arange(0, 10, 1/24), format='jd')
>>> ceres = Orbit.from_horizons('1')
>>> eph = Ephem.from_oo(ceres, epochs, 'G37')
>>> eph
<QTable length=240>
targetname       epoch        ...           obsz               trueanom
d          ...            AU                  deg
str7         float64       ...         float64              float64
---------- ------------------ ... ----------------------- -----------------
1 Ceres  2458519.316966272 ...  3.2083678848104924e-06  68.0863831954328
1 Ceres 2458519.3586329385 ...  2.7022422510736277e-07 68.09589266358881
1 Ceres 2458519.4002996054 ...  -3.111046209036683e-06 68.10540191585879
1 Ceres  2458519.441966272 ...  -6.700369254264427e-06 68.11491095202307
1 Ceres 2458519.4836329385 ... -1.0248419404668141e-05 68.12441977218093
1 Ceres 2458519.5252996054 ... -1.3508703580356052e-05 68.13392837643161
...                ... ...                     ...               ...
1 Ceres  2458529.066966272 ...  1.2522500440509399e-05 70.30569661787204
1 Ceres 2458529.1086329385 ...  1.4101698473351076e-05 70.31515536712485
1 Ceres 2458529.1502996054 ...  1.4771304981564537e-05  70.3246138990413
1 Ceres  2458529.191966272 ...   1.448582020449618e-05 70.33407221340468
1 Ceres 2458529.2336329385 ...   1.326517587380005e-05 70.34353031031534
1 Ceres 2458529.2752996054 ...  1.1193369555934085e-05 70.35298818987367