sentences: a different moon phase occurs approximately once per week
docs: half_moon is phase_of_moon. phase_of_moon is time_period. week has seven_days phase_of_moon is phase. moon has phases full_moon is phase_of_moon. moon's_orbital_period_around_earth is 28_days. blue_moon is long_time. new_moon is phase_of_moon. 1_week has 7_days