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Julian to Gregorian Calendar

Making Up for Lost Time

A Correlation of the Mayan and European ... Volume Fieldiana, Anthropology, v. 17, no.1 (by Thompson, John Eric Sidney, Sir)
Perpetual Calendar and General Reference... (by Goodykoontz, Jasper)
Our Calendar. The Julian Calendar and It... (by Packer, George Nichols)
Japanese Chronological Tables, Showing t... (by Bramsen, William)
Note on the Ancient Mexican Calendar Sys... (by Nutall, Zelia)
A Jewish Calendar for Fifty Years : Cont... (by Lyons, Jacques Judah)

In 46 BC, Julius Caesar proposed reforms to the Roman calendar, which took effect the beginning of 45 BC, and became the predominant calendar throughout the Roman world, Europe, and European settlements including the Americas.

While the Julian calendar is a solar calendar--meaning that its years are based on the time it takes for the Earth to make one revolution around the sun and return to the same exact spot--it was calculated at 365.25 days, creating one extra day every 128 years. In an attempt to account for this imperfection, the Julian calendar interjected a 366-day year every four years and called it a leap year.

Still yet, solar years (also called tropical years) run slightly shorter than the Julian calendar. The years proved that Julius Caesar's strict 4-year leap year calculation too imprecise. By the 16th century, the calendar year was more than slightly off. George Nichols Packer wrote in Our Calendar, "The error, which was 11 minutes and 10.38 seconds every year, was hardly perceptible for a short period, but still amounted to three days every 400 years." Under direction of Pope Gregory XIII, Italian astronomer Aloysus Lilius came up with the Gregorian calendar, fixing the leap year error. Packer wrote:

"[...] by making every centurial year, or the year that completes the century, a common year, if not exactly divisible by 400; so that only every fourth centurial year is leap-year; thus, 1,700, 1,800, and 1,900 are common years, but 2,000, the fourth centurial year, is leap year, and so on." (Our Calendar, p. 36)

In fact, Pope Gregory XIII only commanded the change because the Julian Calendar shifted Easter too many days away from the vernal equinox. The Roman Catholic Church set Easter’s date as the first Sunday after the first full moon after the spring equinox.

By the 20th century, most countries around the world switched to the Gregorian calendar. Throughout history, there have been many calendars, each serving different purposes. One of Mesoamerican Mayan calendar, called the Long Count calendar which plots a 5,126 year cycle, was used to chronologically date historical events, starting with the creation of the world of humankind on August 11, 3114 BC. In use for over one thousand years, the lunar Assyrian calendar named each year after a ruler, with calendar documents describing military exploits.

For further reading on calendars, check out The Perpetual Calendar by Jasper Goodykoontz, Japanese Chronological Tables by William Bramsen, and A Jewish Calendar for Fifty Years by Jacques Judah Lyons.

By Thad Higa