On this day in 1582, Pope Gregory XIII issued a papal bull, Inter Gravissimas, in which he introduced the new Gregorian Calendar—a modification and improvement of the previous Julian Calendar (which had been in use for 1600 years). The new calendar was to go into effect in October and it would "spring forward" by ten days. At the time of the switch, people would go to bed on the night of 4 October 1582 and awaken the next morning, 15 October 1582. This leap forward would correct for centuries of "calendar drift" due to an inaccuracy in the Julian Calendar.
The Julian Calendar, when it was introduced on 1 January 45 BC, was an improvement on the existing Roman Calendar (a lunar calendar). The Julian Calendar was a solar calendar—and it (somewhat accurately) calculated the Sun's transit around the Sun (one year) at 365.25 days. The Julian Calendar understood the necessity of one Leap Day every four years. The problem with the Julian Calendar is that a true Earth Year is 365.2425 days long (slightly shorter than the Julian's 365.25 days). So the Gregorian Calendar removed certain Leap Days, specifically "the centuries" which are not evenly-divisible by 400. Thus, the years 1600, 2000 and 2400 are Leap Years while 1700, 1800 and 1900 are not.
Why do we need such accuracy? Well, the length of a planet's year is the precise amount of time it takes the planet to orbit the Sun. When the calendar is too long (or too short)—even by fractions of a day—key dates drift, in time, into different seasons. For the Church, the traditional observation of Easter was always the Sunday after the first full moon, after the Spring Equinox (usually 21 March). When the calendar year became increasingly inaccurate, it would be possible for Easter to no longer be in the Spring.
After the Pope's decree, Catholic countries quickly fell-in-line. Some Protestant and Orthodox countries, however, took a long time to accept the new calendar. Even today—although most countries use the Gregorian Calendar for secular purposes—some Orthodox churches still follow the Julian calendar to fix the dates of their high holidays.
The Italian sand-cast pewter sandglass, shown above, measures about half-an-hour. Cast into the ends—top and bottom—is a perpetual Roman Calendar, a touch of ancient Italian science. Click on the photo above to learn more about it.
Though our Greenwich Village store is now permanently closed, LEO Design is still alive and well! Please visit our on-line store where we continue to sell Handsome Gifts (www.LEOdesignNYC.com).
To arrange a visit our Pittsburgh showroom (by private appointment only), please call 917-446-4248.