On the lunar calendar, the first day of every month is the new moon, and the fifteenth day of every month is the day of the full moon.
(the first day of every month; is; the new moon; L:On the lunar calendar) (the fifteenth day of every month; is; the day of the full moon)
the first day of every month the fifteenth day of every month
is is
the new moon L:On the lunar calendar
the day of the full moon