def _obliquity_rotation_value(equinox):
"""
Function to calculate obliquity of the earth.
This uses obl06 of erfa.
"""
jd1, jd2 = get_jd12(equinox, "tt")
obl = erfa.obl06(jd1, jd2) * u.radian
return obl.to(u.deg)
def _obliquity_rotation_value(equinox):
"""
Function to calculate obliquity of the earth.
This uses obl06 of erfa.
"""
jd1, jd2 = get_jd12(equinox, "tt")
obl = erfa.obl06(jd1, jd2) * u.radian
return obl.to(u.deg)
def _true_ecliptic_rotation_matrix(equinox):
# This code calls pnm06a from ERFA, which retrieves the precession
# matrix (including frame bias) according to the IAU 2006 model, and
# including the nutation. This family of systems is less popular
# (see https://github.com/astropy/astropy/pull/6508).
jd1, jd2 = get_jd12(equinox, 'tt')
rnpb = erfa.pnm06a(jd1, jd2)
obl = erfa.obl06(jd1, jd2)*u.radian
return matrix_product(rotation_matrix(obl, 'x'), rnpb)
def _mean_ecliptic_rotation_matrix(equinox):
# This code calls pmat06 from ERFA, which retrieves the precession
# matrix (including frame bias) according to the IAU 2006 model, but
# leaves out the nutation. This matches what ERFA does in the ecm06
# function and also brings the results closer to what other libraries
# give (see https://github.com/astropy/astropy/pull/6508).
jd1, jd2 = get_jd12(equinox, 'tt')
rbp = erfa.pmat06(jd1, jd2)
obl = erfa.obl06(jd1, jd2)*u.radian
return matrix_product(rotation_matrix(obl, 'x'), rbp)
def _ecliptic_rotation_matrix(equinox):
# This code calls pmat06 from ERFA, which retrieves the precession
# matrix (including frame bias) according to the IAU 2006 model, but
# leaves out the nutation. This matches what ERFA does in the ecm06
# function and also brings the results closer to what other libraries
# give (see https://github.com/astropy/astropy/pull/6508). However,
# notice that this makes the name "TrueEcliptic" misleading, and might
# be changed in the future (discussion in the same pull request)
jd1, jd2 = get_jd12(equinox, 'tt')
rbp = erfa.pmat06(jd1, jd2)
obl = erfa.obl06(jd1, jd2)*u.radian
return matrix_product(rotation_matrix(obl, 'x'), rbp)
def _ecliptic_rotation_matrix(equinox):
# This code calls pmat06 from ERFA, which retrieves the precession
# matrix (including frame bias) according to the IAU 2006 model, but
# leaves out the nutation. This matches what ERFA does in the ecm06
# function and also brings the results closer to what other libraries
# give (see https://github.com/astropy/astropy/pull/6508). However,
# notice that this makes the name "TrueEcliptic" misleading, and might
# be changed in the future (discussion in the same pull request)
jd1, jd2 = get_jd12(equinox, 'tt')
rbp = erfa.pmat06(jd1, jd2)
obl = erfa.obl06(jd1, jd2) * u.radian
return matrix_product(rotation_matrix(obl, 'x'), rbp)
def mean_obliquity_of_ecliptic(t='now'):
"""
Returns the mean obliquity of the ecliptic, using the IAU 2006 definition. No correction for
nutation is included.
Parameters
----------
t : {parse_time_types}
Time to use in a parse-time-compatible format
"""
time = parse_time(t)
jd1, jd2 = get_jd12(time, 'tt')
obl = erfa.obl06(jd1, jd2) * u.radian
return Angle(obl, u.arcsec)
def mean_obliquity_of_ecliptic(t='now'):
"""
Returns the mean obliquity of the ecliptic, using the IAU 2006 definition. No correction for
nutation is included.
Parameters
----------
t : {parse_time_types}
A time (usually the start time) specified as a parse_time-compatible
time string, number, or a datetime object.
"""
time = parse_time(t)
jd1, jd2 = get_jd12(time, 'tt')
obl = erfa.obl06(jd1, jd2)*u.radian
return Angle(obl, u.arcsec)
def true_obliquity_of_ecliptic(t='now'):
"""
Returns the true obliquity of the ecliptic, using the IAU 2006 definition. Correction for
nutation is included.
Parameters
----------
t : {parse_time_types}
Time to use in a parse-time-compatible format
Notes
-----
The nutation model is IAU 2000A nutation with adjustments to match IAU 2006 precession.
"""
time = parse_time(t)
jd1, jd2 = get_jd12(time, 'tt')
obl = erfa.obl06(jd1, jd2) * u.radian
_, nut_obl = erfa.nut06a(jd1, jd2) * u.radian
obl += nut_obl
return Angle(obl, u.arcsec)
def true_obliquity_of_ecliptic(t='now'):
"""
Returns the true obliquity of the ecliptic, using the IAU 2006 definition. Correction for
nutation is included.
Parameters
----------
t : {parse_time_types}
A time (usually the start time) specified as a parse_time-compatible
time string, number, or a datetime object.
Notes
-----
The nutation model is IAU 2000A nutation with adjustments to match IAU 2006 precession.
"""
time = parse_time(t)
jd1, jd2 = get_jd12(time, 'tt')
obl = erfa.obl06(jd1, jd2)*u.radian
_, nut_obl = erfa.nut06a(jd1, jd2)*u.radian
obl += nut_obl
return Angle(obl, u.arcsec)
def _rotation_matrix_obliquity(time):
"""
Return the rotation matrix from Earth equatorial to ecliptic coordinates
"""
return rotation_matrix(obl06(*get_jd12(time, 'tt')) * u.radian, 'x')
