The changing phases of the Moon have for thousands of years helped
people to mark and reckon the passage of time, and many traditional
festivals are scheduled using the phases of the moon, or a combination
of the lunar and solar cycles.
Easter Sunday, for example, is the first Sunday on or after the first full moon after the spring equinox, whereas the Chinese New Year is celebrated on a new moon - almost always the second new moon after the winter solstice.