Easter

From Turtledove

Easter is a Christian holiday commemorating the Resurrection of Jesus Christ. It is observed on the first Sunday after the first full moon after the vernal equinox, called the Paschal Moon, and is preceded by the six-week period of prayer and fasting known as Lent.

In 1598, disagreement between the Julian and Gregorian Calendars led Catholics and Protestants to mark Easter on different days. In England, where Catholic authorities were persecuting Protestants, the English Inquisition used this difference to uncover Protestants who had concealed their identity.