In October 1582, Pope Gregory XIII introduced the Gregorian calendar as a correction of the Julian calendar, because the latter has too many leap years that cause it to drift out of alignment with the solar year. This has liturgical significance since calculation of the date of Easter assumes that spring Equinox in the Northern Hemisphere occurs on 21 March. To correct the accumulated error, he ordained the date be advanced by ten days. Most Roman Catholic countries adopted the new calendar immediately and Protestant countries followed suit over the following 200 years. In particular, the British Empire (including the American colonies) did so from 1752 with the Calendar (New Style) Act 1750, by which time the divergence had grown to eleven days. This meant that Christmas Day on 25 December ('New Style) was eleven days earlier than it would have been but for the Act, making "Old Christmas" December ('Old Style') happen on 5 January (NS). In February 1800, the Julian calendar had another leap year but the Gregorian did not, moving Old Christmas to 6 January (NS), which coincided with the Feast of the Epiphany.