def test_earth_apparent_heliocentric_position():
"""Tests the apparent_heliocentric_position() method of Earth class"""
epoch = Epoch(1992, 10, 13.0)
lon, lat, r = Earth.apparent_heliocentric_position(epoch)
assert abs(round(lon.to_positive(), 6) - 19.905986) < TOL, \
"ERROR: 1st apparent_heliocentric_position() test doesn't match"
assert lat.dms_str(n_dec=3) == "-0.721''", \
"ERROR: 2nd apparent_heliocentric_position() test doesn't match"
assert abs(round(r, 8) - 0.99760852) < TOL, \
"ERROR: 3rd apparent_heliocentric_position() test doesn't match"
def apparent_geocentric_position(epoch, nutation=True):
"""This method computes the apparent geocentric position of the Sun
for a given epoch, using the VSOP87 theory.
:param epoch: Epoch to compute Sun position, as an Epoch object
:type epoch: :py:class:`Epoch`
:param nutation: Whether the nutation correction will be applied
:type epoch: bool
:returns: A tuple with the heliocentric longitude and latitude (as
:py:class:`Angle` objects), and the radius vector (as a float,
in astronomical units), in that order
:rtype: tuple
:raises: TypeError if input values are of wrong type.
>>> epoch = Epoch(1992, 10, 13.0)
>>> lon, lat, r = Sun.apparent_geocentric_position(epoch)
>>> print(lon.to_positive().dms_str(n_dec=3))
199d 54' 21.548''
>>> print(lat.dms_str(n_dec=3))
0.721''
>>> print(round(r, 8))
0.99760852
"""
# NOTE: In page 169, Meeus gives a different value for the LONGITUDE
# (199d 54' 21.818'') as the one presented above (199d 54' 21.548'').
# After many checks and tests, I came to the conclusion that the result
# above is the right one, and Meeus' result is wrong.
# On the other hand, the difference in LATITUDE may be due to the fact
# that this software uses the complete set of VSOP87C terms, instead of
# the abridged version in Meeus' book.
# First check that input values are of correct types
if not isinstance(epoch, Epoch):
raise TypeError("Invalid input type")
# Use Earth heliocentric position to compute Sun's geocentric position
lon, lat, r = Earth.apparent_heliocentric_position(epoch, nutation)
lon = lon.to_positive() + 180.0
lat = -lat
return lon, lat, r