def test_horizons_consistency_with_precision():
"""
A test to compare at high precision against output of JPL horizons.
Tests ephemerides, and conversions from ICRS to GCRS to TETE. We are aiming for
better than 2 milli-arcsecond precision.
We use the Moon since it is nearby, and moves fast in the sky so we are
testing for parallax, proper handling of light deflection and aberration.
"""
# JPL Horizon values for 2020_04_06 00:00 to 23:00 in 1 hour steps
# JPL Horizons has a known offset (frame bias) of 51.02 mas in RA. We correct that here
ra_apparent_horizons = [
170.167332531, 170.560688674, 170.923834838, 171.271663481, 171.620188972, 171.985340827,
172.381766539, 172.821772139, 173.314502650, 173.865422398, 174.476108551, 175.144332386,
175.864375310, 176.627519827, 177.422655853, 178.236955730, 179.056584831, 179.867427392,
180.655815385, 181.409252074, 182.117113814, 182.771311578, 183.366872837, 183.902395443
] * u.deg + 51.02376467 * u.mas
dec_apparent_horizons = [
10.269112037, 10.058820647, 9.837152044, 9.603724551, 9.358956528, 9.104012390, 8.840674927,
8.571162442, 8.297917326, 8.023394488, 7.749873882, 7.479312991, 7.213246666, 6.952732614,
6.698336823, 6.450150213, 6.207828142, 5.970645962, 5.737565957, 5.507313851, 5.278462034,
5.049521497, 4.819038911, 4.585696512
] * u.deg
with solar_system_ephemeris.set('de430'):
loc = EarthLocation.from_geodetic(-67.787260*u.deg, -22.959748*u.deg, 5186*u.m)
times = Time('2020-04-06 00:00') + np.arange(0, 24, 1)*u.hour
astropy = get_body('moon', times, loc)
apparent_frame = TETE(obstime=times, location=loc)
astropy = astropy.transform_to(apparent_frame)
usrepr = UnitSphericalRepresentation(ra_apparent_horizons, dec_apparent_horizons)
horizons = apparent_frame.realize_frame(usrepr)
assert_quantity_allclose(astropy.separation(horizons), 0*u.mas, atol=1.5*u.mas)
def earth_pos_mcmf(obstime):
"""
Get the position of the Earth in the MCMF frame.
Used for tests.
"""
solar_system_ephemeris.set('jpl')
spkurls = [url for url in get_cached_urls() if 'spk' in url]
for url in spkurls:
# Roundabout way to get the path of the cached spk file.
fpath = download_file(url, cache=True, show_progress=False)
spice.furnsh(fpath)
et = (obstime - Time("J2000")).sec
earthpos, ltt = spice.spkpos('earth', et, 'MOON_ME', 'None', 'moon')
earthpos = unit.Quantity(earthpos, 'km')
return MCMF(*earthpos, obstime=obstime)