callhorizons module

CALLHORIZONS - a Python interface to access JPL HORIZONS ephemerides and orbital elements.

This module provides a convenient python interface to the JPL HORIZONS system by directly accessing and parsing the HORIZONS website. Ephemerides can be obtained through get_ephemerides, orbital elements through get_elements. Function export2pyephem provides an interface to the PyEphem module.

michael.mommert (at) nau.edu, latest version: v1.0.1, 2016-07-19. This code is inspired by code created by Alex Hagen.

v1.0.3: ObsEclLon and ObsEclLat added to get_ephemerides v1.0.2: Python 3.5 compatibility implemented v1.0.1: get_ephemerides fixed v1.0: bugfixes completed, planets/satellites accessible, too v0.9: first release

class callhorizons.query(targetname, smallbody=True, cap=True)[source]

Bases: object

__dict__ = mappingproxy({'__module__': 'callhorizons', '__init__': <function query.__init__>, 'parse_comet': <function query.parse_comet>, 'parse_asteroid': <function query.parse_asteroid>, 'isorbit_record': <function query.isorbit_record>, 'iscomet': <function query.iscomet>, 'isasteroid': <function query.isasteroid>, 'set_epochrange': <function query.set_epochrange>, 'set_discreteepochs': <function query.set_discreteepochs>, 'fields': <property object>, '__len__': <function query.__len__>, 'dates': <property object>, 'query': <property object>, 'dates_jd': <property object>, '__repr__': <function query.__repr__>, '__str__': <function query.__str__>, '__getitem__': <function query.__getitem__>, 'get_ephemerides': <function query.get_ephemerides>, 'get_elements': <function query.get_elements>, 'export2pyephem': <function query.export2pyephem>, '__dict__': <attribute '__dict__' of 'query' objects>, '__weakref__': <attribute '__weakref__' of 'query' objects>, '__doc__': None})
__getitem__(key)[source]

provides access to query data

Parameters:key – str/int; epoch index or property key
Returns:query data according to key
__init__(targetname, smallbody=True, cap=True)[source]

Initialize query to Horizons

Parameters:
  • targetname – HORIZONS-readable target number, name, or designation
  • smallbody – boolean use smallbody=False if targetname is a planet or spacecraft (optional, default: True)
  • cap – boolean set to True to return the current apparition for comet targets.
Returns:

None

__len__()[source]

returns total number of epochs that have been queried

__module__ = 'callhorizons'
__repr__()[source]

returns brief query information

__str__()[source]

returns information on the current query as string

__weakref__

list of weak references to the object (if defined)

dates

returns list of epochs that have been queried (format ‘YYYY-MM-DD HH-MM-SS’)

dates_jd

returns list of epochs that have been queried (Julian Dates)

export2pyephem(center='500@10', equinox=2000.0)[source]

Call JPL HORIZONS website to obtain orbital elements based on the provided targetname, epochs, and center code and create a PyEphem (http://rhodesmill.org/pyephem/) object. This function requires PyEphem to be installed.

Parameters:
  • center – str; center body (default: 500@10 = Sun)
  • equinox – float; equinox (default: 2000.0)
Result:

list; list of PyEphem objects, one per epoch

Example:
>>> import callhorizons
>>> import numpy
>>> import ephem
>>>
>>> ceres = callhorizons.query('Ceres')
>>> ceres.set_epochrange('2016-02-23 00:00', '2016-02-24 00:00', '1h')
>>> ceres_pyephem = ceres.export2pyephem()
>>>
>>> nau = ephem.Observer() # setup observer site
>>> nau.lon = -111.653152/180.*numpy.pi
>>> nau.lat = 35.184108/180.*numpy.pi
>>> nau.elevation = 2100 # m
>>> nau.date = '2015/10/5 01:23' # UT
>>> print ('next rising: %s' % nau.next_rising(ceres_pyephem[0]))
>>> print ('next transit: %s' % nau.next_transit(ceres_pyephem[0]))
>>> print ('next setting: %s' % nau.next_setting(ceres_pyephem[0]))
fields

returns list of available properties for all epochs

get_elements(center='500@10')[source]

Call JPL HORIZONS website to obtain orbital elements based on the provided targetname, epochs, and center code. For valid center codes, please refer to http://ssd.jpl.nasa.gov/horizons.cgi

Parameters:

center – str; center body (default: 500@10 = Sun)

Result:

int; number of epochs queried

Example:
>>> ceres = callhorizons.query('Ceres')
>>> ceres.set_epochrange('2016-02-23 00:00', '2016-02-24 00:00', '1h')
>>> print (ceres.get_elements(), 'epochs queried')
The queried properties and their definitions are:
Property Definition
targetname official number, name, designation [string]
H absolute magnitude in V band (float, mag)
G photometric slope parameter (float)
datetime_jd epoch Julian Date (float)
e eccentricity (float)
p periapsis distance (float, au)
a semi-major axis (float, au)
incl inclination (float, deg)
node longitude of Asc. Node (float, deg)
argper argument of the perifocus (float, deg)
Tp time of periapsis (float, Julian Date)
meananomaly mean anomaly (float, deg)
trueanomaly true anomaly (float, deg)
period orbital period (float, Earth yr)
Q apoapsis distance (float, au)
get_ephemerides(observatory_code, airmass_lessthan=99, solar_elongation=(0, 180), skip_daylight=False)[source]

Call JPL HORIZONS website to obtain ephemerides based on the provided targetname, epochs, and observatory_code. For a list of valid observatory codes, refer to http://minorplanetcenter.net/iau/lists/ObsCodesF.html

Parameters:
  • observatory_code – str/int; observer’s location code according to Minor Planet Center
  • airmass_lessthan – float; maximum airmass (optional, default: 99)
  • solar_elongation – tuple; permissible solar elongation range (optional, deg)
  • skip_daylight – boolean; crop daylight epoch during query (optional)
Result:

int; number of epochs queried

Example:
>>> ceres = callhorizons.query('Ceres')
>>> ceres.set_epochrange('2016-02-23 00:00', '2016-02-24 00:00', '1h')
>>> print (ceres.get_ephemerides(568), 'epochs queried')
The queried properties and their definitions are:
Property Definition
targetname official number, name, designation [string]
H absolute magnitude in V band (float, mag)
G photometric slope parameter (float)
datetime epoch date and time (str, YYYY-MM-DD HH:MM:SS)
datetime_jd epoch Julian Date (float)
solar_presence information on Sun’s presence (str)
lunar_presence information on Moon’s presence (str)
RA target RA (float, J2000.0)
DEC target DEC (float, J2000.0)
RA_rate target rate RA (float, arcsec/s)
DEC_rate target RA (float, arcsec/s, includes cos(DEC))
AZ Azimuth meas East(90) of North(0) (float, deg)
EL Elevation (float, deg)
airmass target optical airmass (float)
magextinct V-mag extinction due airmass (float, mag)
V V magnitude (comets: total mag) (float, mag)
illumination fraction of illuminated disk (float)
EclLon heliocentr. ecl. long. (float, deg, J2000.0)
EclLat heliocentr. ecl. lat. (float, deg, J2000.0)
ObsEclLon obscentr. ecl. long. (float, deg, J2000.0)
ObsEclLat obscentr. ecl. lat. (float, deg, J2000.0)
r heliocentric distance (float, au)
r_rate heliocentric radial rate (float, km/s)
delta distance from the observer (float, au)
delta_rate obs-centric radial rate (float, km/s)
lighttime one-way light time (float, s)
elong solar elongation (float, deg)
elongFlag app. position relative to Sun (str)
alpha solar phase angle (float, deg)
sunTargetPA PA of Sun->target vector (float, deg, EoN)
velocityPA PA of velocity vector (float, deg, EoN)
GlxLon galactic longitude (float, deg)
GlxLat galactic latitude (float, deg)
RA_3sigma 3sigma pos. unc. in RA (float, arcsec)
DEC_3sigma 3sigma pos. unc. in DEC (float, arcsec)
isasteroid()[source]

True if targetname appears to be an asteroid.

iscomet()[source]

True if targetname appears to be a comet.

isorbit_record()[source]

True if targetname appears to be a comet orbit record number.

NAIF record numbers are 6 digits, begin with a ‘9’ and can change at any time.

parse_asteroid()[source]

Parse targetname as if it were a asteroid.

Returns:string or None; The designation of the asteroid or None if targetname does not appear to be an asteroid name.
Example:the following table shows the result of the parsing:
targetname des
1 1
(2 Pallas) 2
(2001) Einstein 2001
2001 AT1 2001 AT1
(1714) Sy 1714
1714 SY 1714 SY
2014 MU69 2014 MU69
2017 AA 2017 AA
parse_comet()[source]

Parse targetname as if it were a comet.

Returns:string or None; The designation of the comet or None if targetname does not appear to be a comet name. Note that comets starting with ‘X/’ are allowed, but this designation indicates a comet without an orbit, so query() should fail.
Example:the following table shows the result of the parsing:
targetname des
1P/Halley 1P
3D/Biela 3D
9P/Tempel 1 9P
73P/Schwassmann Wachmann 3 C 73P (note the missing “C”)
73P-C/Schwassmann Wachmann 3 C 73P-C
73P-BB 73P-BB
322P 322P
X/1106 C1 X/1106 C1
P/1994 N2 (McNaught-Hartley) P/1994 N2
P/2001 YX127 (LINEAR) P/2001 YX127
C/-146 P1 C/-146 P1
C/2001 A2-A (LINEAR) C/2001 A2-A
C/2013 US10 C/2013 US10
C/2015 V2 (Johnson) C/2015 V2
query

returns URL that has been used in calling HORIZONS

set_discreteepochs(discreteepochs)[source]

Set a list of discrete epochs, epochs have to be given as Julian Dates

Parameters:

discreteepochs – array_like list or 1D array of floats or strings

Returns:

None

Example:
>>> import callhorizons
>>> ceres = callhorizons.query('Ceres')
>>> ceres.set_discreteepochs([2457446.177083, 2457446.182343])
set_epochrange(start_epoch, stop_epoch, step_size)[source]

Set a range of epochs, all times are UT

Parameters:
  • start_epoch – str; start epoch of the format ‘YYYY-MM-DD [HH-MM-SS]’
  • stop_epoch – str; final epoch of the format ‘YYYY-MM-DD [HH-MM-SS]’
  • step_size – str; epoch step size, e.g., ‘1d’ for 1 day, ‘10m’ for 10 minutes...
Returns:

None

Example:
>>> import callhorizons
>>> ceres = callhorizons.query('Ceres')
>>> ceres.set_epochrange('2016-02-26', '2016-10-25', '1d')

Note that dates are mandatory; if no time is given, midnight is assumed.