Orbit¶

class sbpy.data.Orbit[source]¶

Bases: DataClass

Class for querying, manipulating, integrating, and fitting orbital elements

Methods Summary

`D_criterion`(obj[, version])	Evaluate orbit similarity D-criterion
`from_horizons`(targetids[, id_type, epochs, ...])	Load target orbital elements from JPL Horizons using `astroquery.jplhorizons.HorizonsClass.elements`
`from_mpc`(targetids[, id_type, target_type])	Load latest orbital elements from the Minor Planet Center.
`oo_propagate`(epochs[, dynmodel, ephfile])	Uses pyoorb to propagate this `Orbit` object.
`oo_transform`(orbittype[, ephfile])	Uses pyoorb to transform this orbit object to a different orbit type definition.
`tisserand`([planet, epoch])	Tisserand parameter with respect to a planet

Methods Documentation

D_criterion(obj, version='sh')[source]¶

Evaluate orbit similarity D-criterion

Three different versions of D-criterion are defined and often compared to each other, includingthe Southworth-Hawkins function [SH63], Drummond function [D81], and the hybrid version [J93]. See review by [W19].

Parameters:

objOrbit object: Object(s) against which to calculate D-criterion
version[‘sh’, ‘d’, ‘h’], optional: Select the versions of D-criterion formula. Case insensitive. ‘sh’ : Southworth-Hawkins function ‘d’ : Drummond function ‘h’ : Hybrid function See references for the details of each version.

Returns:

float or numpy.ndarray

References

[SH63]

Southwarth, R. B., & Hawkins, G. S. 1963, SCoA, 7, 261

[D81]

Drummond, J. D. 1981, Icarus 45, 545

[J93]

Jopek, T. J. 1993, Icarus 106, 603

[W19]

Williams, I. P., Jopek, T. J., Rudawska, R., Tóth, J., Kornoš, L. 2019, In: Ryabova, G. O., Asher, D. J., Compbell-Brown M. D., eds.), Cambridge, UK: Cambridge University Press, 210-234.

Examples

>>> from sbpy.data import Orbit
>>> comets = Orbit.from_horizons(['252P', 'P/2016 BA14'],
...     id_type='designation', closest_apparition=True)
...     
>>> # Southworth & Hawkins function
>>> D_SH = comets[0].D_criterion(comets[1]) 
>>> # Drummond function
>>> D_D = comets[0].D_criterion(comets[1], version='d') 
>>> # hybrid function
>>> D_H = comets[0].D_criterion(comets[1], version='h') 

classmethod from_horizons(targetids, id_type='smallbody', epochs=None, center='500@10', **kwargs)[source]¶

Load target orbital elements from JPL Horizons using astroquery.jplhorizons.HorizonsClass.elements

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 or dict, optional: Epochs of elements to be queried; requires a Time object with a single or 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 TDB; if not, they will be converted to TDB and a TimeScaleWarning will be raised. Default: None
centerstr, optional, default '500@10' (center of the Sun): Elements will be provided relative to this position.
**kwargsoptional: Arguments that will be provided to astroquery.jplhorizons.HorizonsClass.elements.

Returns:

Orbit object

Notes

For detailed explanations of the queried fields, refer to astroquery.jplhorizons.HorizonsClass.elements and the JPL Horizons documentation.
By default, elements are provided in the J2000.0 reference system and relative to the ecliptic and mean equinox of the reference epoch. Different settings can be chosen using additional keyword arguments as used by astroquery.jplhorizons.HorizonsClass.elements.

Examples

>>> from sbpy.data import Orbit
>>> from astropy.time import Time
>>> epoch = Time('2018-05-14', scale='tdb')  
>>> eph = Orbit.from_horizons('Ceres', epochs=epoch)  

classmethod from_mpc(targetids, id_type=None, target_type=None, **kwargs)[source]¶

Load latest orbital elements from the Minor Planet Center.

Parameters:

targetidsstr or iterable of str: Target identifier, resolvable by the Minor Planet Ephemeris Service. If multiple targetids are provided in a list, the same format (number, name, or designation) must be used.
id_typestr, optional: 'name', 'number', 'designation', or None to indicate type of identifiers provided in targetids. If None, automatic identification is attempted using names. Default: None
target_typestr, optional: 'asteroid', 'comet', or None to indicate target type. If None, automatic identification is attempted using names. Default: None
**kwargsoptional: Additional keyword arguments are passed to query_object

Returns:

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

Examples

>>> from sbpy.data import Orbit
>>> orb = Orbit.from_mpc('Ceres') 
>>> orb  
<QTable length=1>
 absmag    Q      arc      w     ...     a        Tj   moid_uranus moid_venus
  mag      AU      d      deg    ...     AU                 AU         AU
float64 float64 float64 float64  ...  float64  float64   float64    float64
------- ------- ------- -------- ... --------- ------- ----------- ----------
   3.34    2.98 79653.0 73.59764 ... 2.7691652     3.3     15.6642    1.84632

oo_propagate(epochs, dynmodel='N', ephfile='de430')[source]¶

Uses pyoorb to propagate this Orbit object. 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 object
absolute magnitude ('H') in mag
photometric phase slope ('G')

Parameters:

epochsTime object: Epoch to which the orbit will be propagated to. Must be a Time object holding a single epoch or multiple epochs (see Epochs and the use of astropy.time). The resulting Orbit object will have the same time scale as epochs.
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:

Orbit object

Examples

Propagate the orbit of Ceres 100 days into the future:

>>> from sbpy.data import Orbit
>>> from astropy.time import Time
>>> epoch = Time(Time.now().jd + 100, format='jd')
>>> ceres = Orbit.from_horizons('Ceres')      
>>> future_ceres = ceres.oo_propagate(epoch)  
>>> print(future_ceres)  
<QTable length=1>
   id           a                  e          ...    H       G    timescale
                AU                            ...   mag
  str7       float64            float64       ... float64 float64    str3
------- ----------------- ------------------- ... ------- ------- ---------
1 Ceres 2.769331727251861 0.07605371361208543 ...    3.34    0.12       UTC

oo_transform(orbittype, ephfile='de430')[source]¶

Uses pyoorb to transform this orbit object to a different orbit type definition. 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 object
absolute magnitude ('H') in mag
photometric phase slope ('G')

Parameters:

orbittypestr: Orbit definition to be transformed to; available orbit definitions are KEP (Keplerian elements), CART (cartesian elements), COM (cometary elements).
ephfilestr, optional: Planet and Lunar ephemeris file version as provided by JPL to be used in the propagation. Default: 'de430'

Returns:

Orbit object

Examples

Obtain the current state vector (cartesian definition, CART) for asteroid Ceres.

>>> from sbpy.data import Orbit
>>> ceres = Orbit.from_horizons('Ceres')  
>>> statevec = ceres.oo_transform('CART') 
>>> print(statevec)  
<QTable length=1>
   id           x                   y          ...    H       G    timescale
                AU                  AU         ...   mag
  str7       float64             float64       ... float64 float64    str2
------- ------------------ ------------------- ... ------- ------- ---------
1 Ceres -1.967176101061908 -1.7891189971612211 ...    3.34    0.12        TT

tisserand(planet='599', epoch=None)[source]¶

Tisserand parameter with respect to a planet

Parameters:

planetstr, Orbit object, or sequence of str, optional: Planet(s) against which the Tisserand parameter is calculated. If str, then the orbital elements of the planet will be automaticallyl pulled from JPL Horizons. If self and/or planet contains more than one object, then numpy broadcasting rules apply. Default is Jupiter.
epochTime, optional: The epoch of planet orbit if pulled from JPL Horizons. This parameter will be passed to from_horizons. If the planet orbit is passed directly, then this parameter has no effect.

Returns:

u.Quantity: The Tisserand parameter(s)

References

Levison, H. F., Duncan, M. J. 1997, Icarus 127, 13

Examples

>>> from sbpy.data import Orbit
>>> comets = Orbit.from_horizons(['252P', 'P/2016 BA14'],
...     id_type='designation', closest_apparition=True)
...     
>>> T_J = comets.tisserand() 
>>>
>>> halley = Orbit.from_horizons('1P', id_type='designation',
...     closest_apparition=True) 
>>> T = halley.tisserand(['599', '699', '799', '899']) 

Navigation

Orbit¶