def new_year(cls, gregorian_year):
"""Return fixed date of Observational (classical)
Nisan 1 occurring in Gregorian year, 'gregorian_year'."""
jan1 = GregorianDate.new_year(gregorian_year)
equinox = Solar.solar_longitude_after(Astro.SPRING, jan1)
sset = JAFFA.universal_from_standard(JAFFA.sunset(ifloor(equinox)))
return cls.phasis_on_or_after(ifloor(equinox) - (14 if (equinox < sset) else 13), JAFFA)
def solar_longitude_on_or_after(cls, lam, fixed_date):
"""Return moment (Beijing time) of the first date on or after
fixed date, 'fixed_date', (Beijing time) when the solar longitude
will be 'lam' degrees."""
tee = Solar.solar_longitude_after(lam, cls.location(fixed_date).universal_from_standard(fixed_date))
return cls.location(tee).standard_from_universal(tee)
