"""
Ephemeris calculations using SunPy coordinate frames
"""
import numpy as np
from packaging import version
import astropy.units as u
from astropy.constants import c as speed_of_light
from astropy.coordinates import (
ICRS,
HeliocentricEclipticIAU76,
SkyCoord,
get_body_barycentric,
get_body_barycentric_posvel,
)
from astropy.coordinates.representation import (
CartesianDifferential,
CartesianRepresentation,
SphericalRepresentation,
)
from astropy.time import Time
from sunpy import log
from sunpy.time import parse_time
from sunpy.time.time import _variables_for_parse_time_docstring
from sunpy.util.decorators import add_common_docstring
from .frames import HeliographicStonyhurst
__author__ = "Albert Y. Shih"
__email__ = "ayshih@gmail.com"
__all__ = ['get_body_heliographic_stonyhurst', 'get_earth',
'get_horizons_coord']
[docs]
@add_common_docstring(**_variables_for_parse_time_docstring())
def get_body_heliographic_stonyhurst(body, time='now', observer=None, *, include_velocity=False,
quiet=False):
"""
Return a `~sunpy.coordinates.frames.HeliographicStonyhurst` frame for the location of a
solar-system body at a specified time. The location can be corrected for light travel time
to an observer.
Parameters
----------
body : `str`
The solar-system body for which to calculate positions
time : {parse_time_types}
Time to use in a parse_time-compatible format
observer : `~astropy.coordinates.SkyCoord`
If None, the returned coordinate is the instantaneous or "true" location.
If not None, the returned coordinate is the astrometric location (i.e., accounts for light
travel time to the specified observer)
include_velocity : `bool`, optional
If True, include the body's velocity in the output coordinate. Defaults to False.
quiet : `bool`, optional
If True, the function will not emit logger output for light-travel-time corrections.
Defaults to False.
Returns
-------
out : `~sunpy.coordinates.frames.HeliographicStonyhurst`
Location of the solar-system body in the `~sunpy.coordinates.HeliographicStonyhurst` frame
Notes
-----
There is no correction for aberration due to observer motion. For a body close to the Sun in
angular direction relative to the observer, the correction can be negligible because the
apparent location of the body will shift in tandem with the Sun.
For planets other than Earth, Astropy's built-in ephemeris is not as accurate as JPL
ephemerides, so one can use `astropy.coordinates.solar_system_ephemeris` to switch
to a JPL ephemeris. See :ref:`astropy-coordinates-solarsystem` for more information, and see
:ref:`sphx_glr_generated_gallery_units_and_coordinates_venus_transit.py` for an example.
Examples
--------
>>> from sunpy.coordinates.ephemeris import get_body_heliographic_stonyhurst
Obtain the location of Venus
>>> get_body_heliographic_stonyhurst('venus', '2012-06-06 04:07:29')
<HeliographicStonyhurst Coordinate (obstime=2012-06-06T04:07:29.000, rsun=695700.0 km): (lon, lat, radius) in (deg, deg, AU)
(0.07349535, 0.05223575, 0.72605496)>
Obtain the location of Venus as seen from Earth when adjusted for light travel time
>>> earth = get_body_heliographic_stonyhurst('earth', '2012-06-06 04:07:29')
>>> get_body_heliographic_stonyhurst('venus', '2012-06-06 04:07:29', observer=earth)
INFO: Apparent body location accounts for 144.07 seconds of light travel time [sunpy.coordinates.ephemeris]
<HeliographicStonyhurst Coordinate (obstime=2012-06-06T04:07:29.000, rsun=695700.0 km): (lon, lat, radius) in (deg, deg, AU)
(0.07084926, 0.0520573, 0.72605477)>
Obtain the location and velocity of Mars
>>> mars = get_body_heliographic_stonyhurst('mars', '2001-02-03', include_velocity=True)
>>> mars
<HeliographicStonyhurst Coordinate (obstime=2001-02-03T00:00:00.000, rsun=695700.0 km): (lon, lat, radius) in (deg, deg, AU)
(63.03105777, -5.20656151, 1.6251161)
(d_lon, d_lat, d_radius) in (arcsec / s, arcsec / s, km / s)
(-0.02323686, 0.00073376, -1.4798387)>
"""
obstime = parse_time(time)
if observer is None:
# If there is no observer, there is not adjustment for light travel time
emitted_time = obstime
else:
observer_icrs = SkyCoord(observer).icrs.cartesian
# This implementation is modeled after Astropy's `_get_apparent_body_position`
light_travel_time = 0.*u.s
emitted_time = obstime
delta_light_travel_time = 1.*u.s # placeholder value
while np.any(np.fabs(delta_light_travel_time) > 1.0e-8*u.s):
body_icrs = get_body_barycentric(body, emitted_time)
distance = (body_icrs - observer_icrs).norm()
delta_light_travel_time = light_travel_time - distance / speed_of_light
light_travel_time = distance / speed_of_light
emitted_time = obstime - light_travel_time
if not quiet:
if light_travel_time.isscalar:
ltt_string = f"{light_travel_time.to_value('s'):.2f}"
else:
ltt_string = f"{light_travel_time.to_value('s')}"
log.info(f"Apparent body location accounts for {ltt_string} "
"seconds of light travel time")
if include_velocity:
pos, vel = get_body_barycentric_posvel(body, emitted_time)
body_icrs = pos.with_differentials(vel.represent_as(CartesianDifferential))
else:
body_icrs = get_body_barycentric(body, emitted_time)
body_hgs = ICRS(body_icrs).transform_to(HeliographicStonyhurst(obstime=obstime))
return body_hgs
[docs]
@add_common_docstring(**_variables_for_parse_time_docstring())
def get_earth(time='now', *, include_velocity=False):
"""
Return a `~astropy.coordinates.SkyCoord` for the location of the Earth at a specified time in
the `~sunpy.coordinates.frames.HeliographicStonyhurst` frame. The longitude will be zero by
definition.
Parameters
----------
time : {parse_time_types}
Time to use in a parse_time-compatible format
include_velocity : `bool`, optional
If True, include the Earth's velocity in the output coordinate. Defaults to False.
Returns
-------
out : `~astropy.coordinates.SkyCoord`
Location of the Earth in the `~sunpy.coordinates.frames.HeliographicStonyhurst` frame
Notes
-----
The Earth's velocity in the output coordinate will invariably be negligible in the longitude
direction because the `~sunpy.coordinates.frames.HeliographicStonyhurst` frame rotates in time
such that the plane of zero longitude (the XZ-plane) tracks Earth.
Examples
--------
>>> from sunpy.coordinates.ephemeris import get_earth
>>> get_earth('2001-02-03 04:05:06')
<SkyCoord (HeliographicStonyhurst: obstime=2001-02-03T04:05:06.000, rsun=695700.0 km): (lon, lat, radius) in (deg, deg, AU)
(0., -6.18656962, 0.98567647)>
>>> get_earth('2001-02-03 04:05:06', include_velocity=True)
<SkyCoord (HeliographicStonyhurst: obstime=2001-02-03T04:05:06.000, rsun=695700.0 km): (lon, lat, radius) in (deg, deg, AU)
(0., -6.18656962, 0.98567647)
(d_lon, d_lat, d_radius) in (arcsec / s, arcsec / s, km / s)
(6.42643739e-11, -0.00279484, 0.24968506)>
>>> get_earth('2001-02-03 04:05:06', include_velocity=True).transform_to('heliocentricinertial')
<SkyCoord (HeliocentricInertial: obstime=2001-02-03T04:05:06.000): (lon, lat, distance) in (deg, deg, AU)
(58.41594489, -6.18656962, 0.98567647)
(d_lon, d_lat, d_distance) in (arcsec / s, arcsec / s, km / s)
(0.0424104, -0.00279484, 0.2496851)>
"""
earth = get_body_heliographic_stonyhurst('earth', time=time, include_velocity=include_velocity)
# Explicitly set the longitude to 0
earth_repr = SphericalRepresentation(0*u.deg, earth.lat, earth.radius)
# Modify the representation in the frame while preserving all differentials (e.g., velocity)
earth = earth.realize_frame(earth_repr.with_differentials(earth.spherical.differentials))
return SkyCoord(earth)
[docs]
@add_common_docstring(**_variables_for_parse_time_docstring())
def get_horizons_coord(body, time='now', id_type=None, *, include_velocity=False):
"""
Queries JPL HORIZONS and returns a `~astropy.coordinates.SkyCoord` for the location of a
solar-system body at a specified time. This location is the instantaneous or "true" location,
and is not corrected for light travel time or observer motion.
.. note::
This function requires the Astroquery package to be installed and
requires an Internet connection.
Parameters
----------
body : `str`
The solar-system body for which to calculate positions. One can also use the search form
linked below to find valid names or ID numbers.
id_type : `None`, `str`
See the astroquery documentation for information on id_types: `astroquery.jplhorizons`.
If the installed astroquery version is less than 0.4.4, defaults to ``'majorbody'``.
time : {parse_time_types}, `dict`
Time to use in a parse_time-compatible format.
Alternatively, this can be a dictionary defining a range of times and
dates; the range dictionary has to be of the form
{{'start': start_time, 'stop': stop_time, 'step':'n[y|d|m|s]'}}.
``start_time`` and ``stop_time`` must be in a parse_time-compatible format,
and are interpreted as UTC time. ``step`` must be a string with either a
number and interval length (e.g. for every 10 seconds, ``'10s'``), or a
plain number for a number of evenly spaced intervals. For more information
see the docstring of `astroquery.jplhorizons.HorizonsClass`.
include_velocity : `bool`, optional
If True, include the body's velocity in the output coordinate. Defaults to False.
Returns
-------
`~astropy.coordinates.SkyCoord`
Location of the solar-system body
Notes
-----
Be aware that there can be discrepancies between the coordinates returned by JPL HORIZONS,
the coordinates reported in mission data files, and the coordinates returned by
`~sunpy.coordinates.get_body_heliographic_stonyhurst`.
References
----------
* `JPL HORIZONS <https://ssd.jpl.nasa.gov/?horizons>`_
* `JPL HORIZONS form to search bodies <https://ssd.jpl.nasa.gov/horizons.cgi?s_target=1#top>`_
* `Astroquery <https://astroquery.readthedocs.io/en/latest/>`_
Examples
--------
>>> from sunpy.coordinates.ephemeris import get_horizons_coord
Query the location of Venus
>>> get_horizons_coord('Venus barycenter', '2001-02-03 04:05:06') # doctest: +REMOTE_DATA
INFO: Obtained JPL HORIZONS location for Venus Barycenter (2) [sunpy.coordinates.ephemeris]
<SkyCoord (HeliographicStonyhurst: obstime=2001-02-03T04:05:06.000, rsun=695700.0 km): (lon, lat, radius) in (deg, deg, AU)
(-33.93155836, -1.64998443, 0.71915147)>
Query the location of the SDO spacecraft
>>> get_horizons_coord('SDO', '2011-11-11 11:11:11') # doctest: +REMOTE_DATA
INFO: Obtained JPL HORIZONS location for Solar Dynamics Observatory (spac [sunpy.coordinates.ephemeris]
<SkyCoord (HeliographicStonyhurst: obstime=2011-11-11T11:11:11.000, rsun=695700.0 km): (lon, lat, radius) in (deg, deg, AU)
(0.01019118, 3.29640728, 0.99011042)>
Query the location of the SOHO spacecraft via its ID number (-21)
>>> get_horizons_coord(-21, '2004-05-06 11:22:33') # doctest: +REMOTE_DATA
INFO: Obtained JPL HORIZONS location for SOHO (spacecraft) (-21) [sunpy.coordinates.ephemeris]
<SkyCoord (HeliographicStonyhurst: obstime=2004-05-06T11:22:33.000, rsun=695700.0 km): (lon, lat, radius) in (deg, deg, AU)
(0.25234902, -3.55863633, 0.99923086)>
Query the location and velocity of the asteroid Juno
>>> get_horizons_coord('Juno', '1995-07-18 07:17', 'smallbody', include_velocity=True) # doctest: +REMOTE_DATA
INFO: Obtained JPL HORIZONS location for 3 Juno (A804 RA) [sunpy.coordinates.ephemeris]
<SkyCoord (HeliographicStonyhurst: obstime=1995-07-18T07:17:00.000, rsun=695700.0 km): (lon, lat, radius) in (deg, deg, AU)
(-25.16107532, 14.59098438, 3.17667664)
(d_lon, d_lat, d_radius) in (arcsec / s, arcsec / s, km / s)
(-0.03306548, 0.00052415, -2.66709222)>
Query the location of Solar Orbiter at a set of 12 regularly sampled times
>>> get_horizons_coord('Solar Orbiter',
... time={{'start': '2020-12-01',
... 'stop': '2020-12-02',
... 'step': '12'}}) # doctest: +REMOTE_DATA
INFO: Obtained JPL HORIZONS location for Solar Orbiter (spacecraft) (-144 [sunpy.coordinates.ephemeris]
...
"""
# Import here so that astroquery is not a module-level dependency
import astroquery
from astroquery.jplhorizons import Horizons
if id_type is None and version.parse(astroquery.__version__) < version.parse('0.4.4'):
# For older versions of astroquery retain default behaviour of this function
# if id_type isn't manually specified.
id_type = 'majorbody'
if isinstance(time, dict):
if set(time.keys()) != set(['start', 'stop', 'step']):
raise ValueError('time dictionary must have the keys ["start", "stop", "step"]')
epochs = time
jpl_fmt = '%Y-%m-%d %H:%M:%S.%f'
epochs['start'] = parse_time(epochs['start']).tdb.strftime(jpl_fmt)
epochs['stop'] = parse_time(epochs['stop']).tdb.strftime(jpl_fmt)
else:
obstime = parse_time(time)
array_time = np.reshape(obstime, (-1,)) # Convert to an array, even if scalar
epochs = array_time.tdb.jd.tolist() # Time must be provided in JD TDB
query = Horizons(id=body, id_type=id_type,
location='500@10', # Heliocentric (mean ecliptic)
epochs=epochs)
try:
result = query.vectors()
except Exception as e: # Catch and re-raise all exceptions, and also provide query URL if generated
if query.uri is not None:
log.error(f"See the raw output from the JPL HORIZONS query at {query.uri}")
raise e
finally:
query._session.close()
log.info(f"Obtained JPL HORIZONS location for {result[0]['targetname']}")
log.debug(f"See the raw output from the JPL HORIZONS query at {query.uri}")
if isinstance(time, dict):
obstime_tdb = parse_time(result['datetime_jd'], format='jd', scale='tdb')
obstime = Time(obstime_tdb, format='isot', scale='utc')
else:
# JPL HORIZONS results are sorted by observation time, so this sorting needs to be undone.
# Calling argsort() on an array returns the sequence of indices of the unsorted list to put the
# list in order. Calling argsort() again on the output of argsort() reverses the mapping:
# the output is the sequence of indices of the sorted list to put that list back in the
# original unsorted order.
unsorted_indices = obstime.argsort().argsort()
result = result[unsorted_indices]
vector = CartesianRepresentation(result['x'], result['y'], result['z'])
if include_velocity:
velocity = CartesianDifferential(result['vx'], result['vy'], result['vz'])
vector = vector.with_differentials(velocity)
coord = SkyCoord(vector, frame=HeliocentricEclipticIAU76, obstime=obstime)
return coord.transform_to(HeliographicStonyhurst).reshape(obstime.shape)
