Medieval festivals that divided the Celtic year were called Quarter Days, each occurring on a solstice or an equinox. In addition, each quarter was halved by four Cross-Quarter Days creating eight annual segments. With the adoption of the twelve month Roman calendar and the establishment of the Church, the Celtic festivals were renamed for feasts of the Church’s liturgical year. The renamed Quarter Days were Lady Day (formerly Ostara, March 25th), Midsummer Day (formerly Litha, June 24th), Michaelmas (formerly Mabon, September 29th), and Yule (December 21st). A mnemonic for remembering when the first three quarter days fell was March has five letters, and Lady Day is March 25th. June has four letters and September nine, with Midsummer Day and Michaelmas falling on the 24th and 29th, respectively. The cross-quarter days were Candlemas (formerly Imbolic, February 2), May Day (formerly Beltane, May 1), Lammas (formerly Lughnasadh, August 1), and All Hallows (formerly Samhain, November 1). Lady Day occurs on the vernal equinox. It is so named because on this day Christ’s incarnation was announced to Mary. Until 1752, it was England’s New Year. It was often the day for hiring farm laborers for the upcoming growing season.
~ Dr. Gil Haas, St. Augustine of Canterbury Episcopal Church