each of the moon 's phases occurs once per month
half_moon is phase_of_moon. solar_month is month. month_of_january has 31_days phase_of_moon is time_period. phase_of_moon is phase. moon has phases full_moon is phase_of_moon. moon's_orbital_period_around_earth is 28_days. new_moon is phase_of_moon. lunar_month is month.