Most of the world's Christians mark time on the solar Gregorian calendar, a late medieval correction of the much-older Julian calendar. Julius Caesar had initiated the calendar named after him in 46
b.c.e., but it was based on some miscalculations. In 1582, Pope Gregory XIII shortened the Julian year by ten days and added a day to February every fourth or "leap" year. Some Eastern Christian churches still use the Julian calendar, so that their major feasts fall just less than two weeks later than those of the Western churches. Until the Gregorian reform, Christians considered March 25 the beginning of the year, since that was judged to be the day on which Gabriel announced to Mary that she would give birth to Jesus. March 25, which had in ancient times been mistakenly calculated as the spring equinox, the first day of spring, remains the Feast of the Annunciation.
For centuries Christians continued to observe the timing of traditional Jewish feasts, which were movable within limits of specific agricultural seasons (such as planting and harvest times). Using the Jewish seven-day week, Christians gradually added fixed feasts, such as those of saints and martyrs. The custom of designating Sunday as a day of religious observance began during the first generation after Jesus' death and Emperor Constantine decreed it a day of rest in 321. Wednesdays and Fridays had anciently been days of fasting, a practice now surviving largely on the first day of Lent, Good Friday, and other Fridays during Lent. For most Christians the year consists of three liturgical seasons, Advent and Christmastide, Lent and an Eastertide that ends with Pentecost Sunday, and "Ordinary" time until the first Sunday of the following Advent. Some Christians in Egypt and Ethiopia still use the solar Coptic calendar, based on the ancient Egyptian reckoning. Recent recalculations suggest that Jesus was actually born closer to 4 b.c.e. than to the year 1.
From The Handy Religion Answer Book, Second Edition by Jack Renard, Ph.D., (c) 2012 Visible Ink Press(R). Your Guide to the World's Major Faiths
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