Joseph Campbell

 Easter is calculated as the Sunday that follows the first moon after the vernal equinox. It is evidence of a concern centuries before Christ to coordinate the lunar and solar calendars.

What we have to recognize is that these celestial bodies represented to the ancients two different modes of eternal life, one engaged in the field of time, like throwing off death, as the moon its shadow, to be born again; the other, disengaged and eternal. The dating of Easter according to both lunar and solar calendars suggests that life, like the light that is reborn in the moon and eternal in the sun, finally is one.