Juliánnaptárat

The Juliánnaptár, or Julian calendar, is a solar calendar that was introduced by Julius Caesar in 46 BCE. It was a reform of the Roman calendar and was in wide use in the Roman Empire and its successor states for over 1,600 years. The Julian calendar is named after Julius Caesar, who commissioned the reform. The calendar was designed by the Alexandrian astronomer Sosigenes and was established by decree by the Roman emperor Julius Caesar in 46 BC.

The Julian calendar has a year of 365 days, with an extra day added every four years to form a leap year. This system results in an average year length of 365.25 days, which is very close to the actual solar year of approximately 365.2422 days. However, this slight inaccuracy meant that the Julian calendar gradually drifted out of sync with the seasons. By the 16th century, the vernal equinox was occurring around March 11th, instead of March 21st as it had in the 4th century.

This drift led to the development and adoption of the Gregorian calendar in 1582 by Pope Gregory XIII. The Gregorian calendar corrected the accumulated error and introduced a more precise rule for leap years, reducing the average year length to 365.2425 days. While the Gregorian calendar is now the most widely used calendar internationally, the Julian calendar continued to be used by various Orthodox Churches for liturgical purposes and in some countries until the 20th century. Some Orthodox churches still use it today for calculating feast days.