callhorizons module

CALLHORIZONS - a Python 2.7 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: v0.9, 2016-02-27. This code is inspired by code created by Alex Hagen.

class callhorizons.query(targetname)

__getitem__(key)

provides access to query data

Parameters:

key : str/int

epoch index or property key

Returns:

query data according to key

__init__(targetname)

Initialize query to Horizons

Parameters:

targetname : str

HORIZONS-readable target number, name, or designation

__len__()

returns total number of epochs that have been queried

__module__ = 'callhorizons'

__repr__()

returns brief query information

__str__()

returns information on the current query as string

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)

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)

Examples

>>> 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')

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)

Examples

>>> 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)

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)

Examples

>>> 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)
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)

set_discreteepochs(discreteepochs)

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

Parameters:

discreteepochs : list

list of floats or strings, maximum length: 15

Returns:

None

Examples

>>> import callhorizons
>>> ceres = callhorizons.query('Ceres')
>>> ceres.set_discreteepochs([2457446.177083, 2457446.182343])

If more than 15 epochs are provided, the list will be cropped to 15 epochs.

set_epochrange(start_epoch, stop_epoch, step_size)

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

Examples

>>> 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.