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 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 _rotation_matrix_obliquity(time): """ Return the rotation matrix from Earth equatorial to ecliptic coordinates """ return rotation_matrix(erfa.obl06(*get_jd12(time, 'tt'))*u.radian, 'x')