Julian calendar
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The Julian calendar is a solar calendar of 365 days in every year with an additional leap day every fourth year. The Julian calendar is still used as a religious calendar in parts of the Eastern Ortho
The Tusculum portrait of Julius Caesar
Russian icon of the Theophany (the baptism of Jesus by John the Baptist) (6 January), the highest-ranked feast which occurs on the fixed cycle of the Eastern Orthodox liturgical calendar
Marine sandglass MMM
Gregorian calendar
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The Gregorian calendar is the calendar used in most parts of the world. It went into effect in October 1582 following the papal bull Inter gravissimas issued by Pope Gregory XIII, which introduced it
Julian calendar
…Orthodox Church and in parts of Oriental Orthodoxy as well as in the Berber calendar. For a quick calculation, between 1901 and 2099 the much more common Gregorian date equals the Julian date plus 13 days (for instance Julian 1 January falls on Gregorian 14 January). The Julian calendar was proposed in 46 BC by (and…
Christopher Clavius (1538–1612), one of the main authors of the reform
Pope Gregory XIII, portrait by Lavinia Fontana, 16th century
First page of the papal bull Inter gravissimas
Detail of the pope's tomb by Camillo Rusconi (completed 1723); Antonio Lilio is genuflecting before the pope, presenting his printed calendar.