The Druids knew that "uneven times" were more prone to produce conscious alteration (Otherworld access) than the "balanced times" of spring and Autumn Equinoxes, paired with their divisors.
Mid-Summer's Day: the day of greatest lunar/nightly imbalance.
Mid-Winter's Day: the day of greatest solar/day-time imbalance.
Beltane: The cross-quarter night which marks the beginning of Summer/The Light Half of the Year.
Samhain: the cross-quarter night which marks the beginning of the Winter/The Dark Half of the Year.
