A year is not an arbitrary period of time, it is an astronomic reality insofar as it represents the time it takes for the earth to orbit around the sun. A good calendar therefore, needs to match this period of time. It takes 365.242 days for the earth to complete the trip. Instead of adding .242 of a day (5 hours 48 minutes and 30 seconds) to a 365-day year the leap-year system was devised. Every four years an extra day was added to the 365 days in the regular calendar thereby creating 366-day years. This system is relatively accurate, but .242 is not exactly the .250 of a day that it needs to be for the leap-day to work perfectly. Over the centuries the .008 of a day (11 minutes 30 seconds) began to accumulate.

The Gregorian calendar is named after Pope Gregory XIII, who drastically altered the Julian calendar for October 1852.

The continuing accumulation caused by the inaccuracies of the Julian calendar came to an end in 1582. Pope Gregory XIII stated that 10 days in October were to be removed from the calendar. Specifically, he struck the 5th through 14th from the month which created a very bizarre October 1582. You can imagine what people's schedule's looked like during that month:

Pope Gregory XIII declared that 10 days were to be removed from the calendar in October 1582.

October 1582 Sun Mon Tue Wed Thur Fri Sat 1 2 3 4 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31

Pope Gregory XIII, whom the modern calendar is named after (Gregorian), also established a system to prevent the accumulation from developing all over again. Every four years divisible by four would continue to be a leap year, but years divisible by 100 would not, unless they are also divisible by 400. The year 2000 was one of these special years that comes once every four centuries. 2000 is divisible by 100 but also divisible by 400 and therefore it is designated as a leap year.

The new Gregorian Calendar is far superior to the inaccurate Julian Calendar that it replaced, but it still not perfect. There are still minuscule accumulations of time and in thousands of years, another correction may have to be enacted.

Perhaps the most interesting event of 1582 (aside from the calendar change), is that William Shakespeare (at age 18) got married to Anne Hathaway in Stratford-upon-Avon.