"The Holidays" are considered to be at the end of the (solar) year, but around the beginning of the year there are a series of holidays which are based upon the phases of the moon. These are determined according to various lunar calendars, which are sometimes called luni-solar calendars, because they are periodically adjusted by adding months to keep them somewhat synchronized with the solar seasons.
The first such holiday is Chinese New Year. It is also celebrated in other Asian countries, and is known as Tet in Viet Nam. Here in San Francisco, there is a large Chinese community (and a somewhat smaller Vietnamese one) so this is an important holiday here. The annual Chinese New Year parade here is famous, but few know that it does not happen on the New Year. The celebration actually lasts for more than two weeks, and the parade is held at the end, or actually on the nearest Saturday. The New Year itself usually begins on the second new moon after winter solstice, which this year is February 14 (MJD 55242), coincidentally on Valentine's Day . The Spring Festival is officially celebrated here on the following full moon on February 28 (55256), which is a Sunday, with the parade on the preceding Saturday. In China, the celebration ends with the Lantern Festival, which is March 1 (55257) this year. This coming year is the Year of the Tiger in Chinese astrology, as was my birth year.
Right after the Chinese New Year is the Catholic holiday, Ash Wednesday. It often falls near the Chinese New Year new moon, or the next new moon a month later. It's usually right after a new moon, but can also be a day or so before. This year it is on February 17 (55244). This marks the beginning of Lent. Growing up in the Catholic Church, I had to go to mass and get ashes on my forehead on Ash Wednesday. The day before is celebrated as Mardi Gras, also known as Carnaval or Shrove Tuesday, which is traditionally the last day to feast before the Lenten fast.
Lent ends on Easter Sunday, which is April 4 (55290) this year. It is the Sunday following the first full moon after March 21, which the Church considers to be the first day of spring in the Gregorian calendar, even when it isn't. This year the full moon is on Tuesday, March 30 (55285) so Easter is the following Sunday. Growing up, this meant that we got to color eggs and eat candy, when we got back from church.
Few in this country know that there are sometimes two Easters, Eastern and Western. This year they coincide, but in the Eastern Orthodox church (and other eastern churches) Easter can sometimes follow in the next Sunday, or after the next full moon, four or five weeks later, because they still use the Julian calendar to compute holidays. I have Greek relations by marriage who celebrate the Orthodox holidays.
I also have Jewish relations by marriage, who celebrate holidays on the Jewish lunar calendar. Originally, Easter was based upon the Jewish holiday of Pesach, or Passover. This holiday lasts seven or eight days, beginning on the full moon that falls on the 14th day of the month of Nisan. Since Jewish days start at sunset, this year that is the evening of Monday, March 29 (55284). Easter often occurs during Passover, as it does this year, but since Christians now use their own calculations, Passover is sometimes a month after Easter. I usually celebrate this with my in-laws. Other Jewish holidays also are connected to the phases of the moon; for instance, the Jewish new year, Rosh Hashanah, is on a new moon near the equinox in September.
Muslims also use a lunar calendar, but theirs is purely lunar, so it drifts every year in relation to the solar calendar. They have holidays on new moons, including the new year (Al-Hajra) and the beginning and end of Ramadan, but these can happen on any date in the Gregorian calendar. The current Muslim year began around December 18 (55548) and Ramadan begins around August 11 (55419). The exact dates depend upon actual observations of the new moon, and can vary from place to place.
So even though we have a solar calendar, for me, at least, the phases of the moon are significant on my social calendar.
21st of Sh'vat, 5770 כ״א בְּשְׁבָט תש״ע