The Gregorian calendar is the calendar that is used nearly everywhere in the world. A modification of the Julian calendar, it was first proposed by the Neapolitan doctor Aloysius Lilius, and was decreed by Pope Gregory XIII, for whom it was named, on 24 February 1582 (Note: The papal bull Inter gravissimas was signed in the year 1581 for unknown reasons, but printed on 1 March 1582. Although the use of the date 1581 is often attributed to the supposed adoption by the papacy of a reckoning by which the year began on 25 March, other contemporaneous papal bulls have years that do not agree with March years, let alo ...

Including:

• Gregorian calendar - History
• Gregorian calendar - Invention
• Gregorian calendar - Beginning of the year
• Gregorian calendar - Adoption outside of Roman Catholic nations
• Gregorian calendar - Proleptic Gregorian calendar
• Gregorian calendar - Confusion with British vs. American usage
• Gregorian calendar - Difference between Gregorian and Julian calendar dates
• Gregorian calendar - Months of the year
• Gregorian calendar - Accuracy
• Gregorian calendar - Calendar seasonal error
• Gregorian calendar - Numerical facts
• Gregorian calendar - Number of leap years starting on a given day of the week
• Gregorian calendar - Days of the week
• Gregorian calendar - Reference

Read more here: » Gregorian calendar: Encyclopedia - Gregorian calendar

Gregorian calendar - Invention. The motivation of the Catholic Church in adjusting the calendar was to have Easter celebrated at the time that they thought had been agreed to at the First Council of Nicaea in 325. Although a canon of the council implies that all churches used the same Easter, they did not. The Church of Alexandria celebrated Easter on the Sunday after the 14th day of the Moon that falls on or after the vernal equinox, which they placed on 21 March. However, the Church of Rome still regarded 25 Ma ...

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Gregorian calendar, Gregorian calendar - History, Gregorian calendar - Invention, Gregorian calendar - Beginning of the year, Gregorian calendar - Adoption outside of Roman Catholic nations, Gregorian calendar - Proleptic Gregorian calendar, Gregorian calendar - Confusion with British vs. American usage, Gregorian calendar - Difference between Gregorian and Julian calendar dates, Gregorian calendar - Months of the year, Gregorian calendar - Accuracy, Gregorian calendar - Calendar seasonal error, Gregorian calendar - Numerical facts, Gregorian calendar - Number of leap years starting on a given day of the week, Gregorian calendar - Days of the week, Gregorian calendar - Reference

Read more here: » Gregorian calendar: Encyclopedia II - Gregorian calendar - History

Because there are 97 leap years in every 400 in the Gregorian Calendar, there should, in each "cycle", be either 13 or 14 leap years starting on each day of the week. However, the effects of the "common" centennial years (1700, 1800, 1900, 2100, 2200 etc.) cause major alterations. This is because the absence of an extra day in such years causes the following leap year (1704, 1804, 1904, 2104 etc.) to start on the same day of the week as the leap year twelve years before (1692, 1792, 1892, 2092 etc.). Similarly, the leap year ei ...

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Gregorian calendar, Gregorian calendar - History, Gregorian calendar - Invention, Gregorian calendar - Beginning of the year, Gregorian calendar - Adoption outside of Roman Catholic nations, Gregorian calendar - Proleptic Gregorian calendar, Gregorian calendar - Confusion with British vs. American usage, Gregorian calendar - Difference between Gregorian and Julian calendar dates, Gregorian calendar - Months of the year, Gregorian calendar - Accuracy, Gregorian calendar - Calendar seasonal error, Gregorian calendar - Numerical facts, Gregorian calendar - Number of leap years starting on a given day of the week, Gregorian calendar - Days of the week, Gregorian calendar - Reference

Read more here: » Gregorian calendar: Encyclopedia II - Gregorian calendar - Number of leap years starting on a given day of the week

January 1 of any year whose number is a multiple of 400 is a Saturday. From this you can work out the day of the week of any date. See also: Days of the week Calculating the day of the week ...

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Gregorian calendar, Gregorian calendar - History, Gregorian calendar - Invention, Gregorian calendar - Beginning of the year, Gregorian calendar - Adoption outside of Roman Catholic nations, Gregorian calendar - Proleptic Gregorian calendar, Gregorian calendar - Confusion with British vs. American usage, Gregorian calendar - Difference between Gregorian and Julian calendar dates, Gregorian calendar - Months of the year, Gregorian calendar - Accuracy, Gregorian calendar - Calendar seasonal error, Gregorian calendar - Numerical facts, Gregorian calendar - Number of leap years starting on a given day of the week, Gregorian calendar - Days of the week, Gregorian calendar - Reference

Read more here: » Gregorian calendar: Encyclopedia II - Gregorian calendar - Days of the week

When leap years and common years are taken into account, there are a total of 14 possible Gregorian calendars. When different dates of Easter are also taken into account, there are a total of 70 possible Gregorian calendars. An average year is 365.2425 days = 52.1775 weeks = 8,765.82 hours = 525,949.2 minutes = 31,556,952 seconds. A common year is 365 days = 8,760 hours = 525,600 minutes = 31,536,000 seconds. A leap year is 366 days = 8,784 hours = 527,040 minutes = 31,622,400 seconds. (Some years may also contain one or two leap seconds which can be positive or negative.) See als ...

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Gregorian calendar, Gregorian calendar - History, Gregorian calendar - Invention, Gregorian calendar - Beginning of the year, Gregorian calendar - Adoption outside of Roman Catholic nations, Gregorian calendar - Proleptic Gregorian calendar, Gregorian calendar - Confusion with British vs. American usage, Gregorian calendar - Difference between Gregorian and Julian calendar dates, Gregorian calendar - Months of the year, Gregorian calendar - Accuracy, Gregorian calendar - Calendar seasonal error, Gregorian calendar - Numerical facts, Gregorian calendar - Number of leap years starting on a given day of the week, Gregorian calendar - Days of the week, Gregorian calendar - Reference

Read more here: » Gregorian calendar: Encyclopedia II - Gregorian calendar - Numerical facts

The Gregorian calendar improves the approximation made by the Julian calendar by skipping 3 Julian leap days in every 400 years, giving an average year of 365.2425 mean solar days long, which has an error of about 1 day per 3300 years with respect to the mean tropical year of 365.2422 days but less than half this error with respect to the vernal equinox year of 365.2424 days. Both are substantially more accurate than the 1 day in 128 years error of ...

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Gregorian calendar, Gregorian calendar - History, Gregorian calendar - Invention, Gregorian calendar - Beginning of the year, Gregorian calendar - Adoption outside of Roman Catholic nations, Gregorian calendar - Proleptic Gregorian calendar, Gregorian calendar - Confusion with British vs. American usage, Gregorian calendar - Difference between Gregorian and Julian calendar dates, Gregorian calendar - Months of the year, Gregorian calendar - Accuracy, Gregorian calendar - Calendar seasonal error, Gregorian calendar - Numerical facts, Gregorian calendar - Number of leap years starting on a given day of the week, Gregorian calendar - Days of the week, Gregorian calendar - Reference

Read more here: » Gregorian calendar: Encyclopedia II - Gregorian calendar - Accuracy

The Gregorian calendar can, for certain purposes, be extended backwards to dates preceding its official introduction, producing the proleptic Gregorian Calendar. However, this proleptic calendar should be used with great caution. For ordinary purposes, the dates of events occurring prior to 15 October 1582 are generally shown as they appeared in the Julian calendar, and not converted into their Gregorian equivalents. However, events occurring in countries where the Gregorian calendar was introduced later than 4 October 1 ...

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Gregorian calendar, Gregorian calendar - History, Gregorian calendar - Invention, Gregorian calendar - Beginning of the year, Gregorian calendar - Adoption outside of Roman Catholic nations, Gregorian calendar - Proleptic Gregorian calendar, Gregorian calendar - Confusion with British vs. American usage, Gregorian calendar - Difference between Gregorian and Julian calendar dates, Gregorian calendar - Months of the year, Gregorian calendar - Accuracy, Gregorian calendar - Calendar seasonal error, Gregorian calendar - Numerical facts, Gregorian calendar - Number of leap years starting on a given day of the week, Gregorian calendar - Days of the week, Gregorian calendar - Reference

Read more here: » Gregorian calendar: Encyclopedia II - Gregorian calendar - Proleptic Gregorian calendar

Dates of events in Britain prior to 1752 are usually now shown in their original Old Style form, whereas dates of events in (then British) America prior to 1752 are usually now shown in the New Style form. For example, Shakespeare died on 23 April (OS), and it is rare to see this converted to 3 May (NS). But while George Washington was born on 11 February (OS), his birthday is now celebrated on 22 February (N ...

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Gregorian calendar, Gregorian calendar - History, Gregorian calendar - Invention, Gregorian calendar - Beginning of the year, Gregorian calendar - Adoption outside of Roman Catholic nations, Gregorian calendar - Proleptic Gregorian calendar, Gregorian calendar - Confusion with British vs. American usage, Gregorian calendar - Difference between Gregorian and Julian calendar dates, Gregorian calendar - Months of the year, Gregorian calendar - Accuracy, Gregorian calendar - Calendar seasonal error, Gregorian calendar - Numerical facts, Gregorian calendar - Number of leap years starting on a given day of the week, Gregorian calendar - Days of the week, Gregorian calendar - Reference

Read more here: » Gregorian calendar: Encyclopedia II - Gregorian calendar - Confusion with British vs. American usage

The Gregorian calendar's year is divided into 12 months: English speakers sometimes remember the number of days in each month by the use of the traditional mnemonic verse: Thirty days hath September / April, June and November / All the rest have thirty-one / Excepting February alone / Which has but twenty-eight, in fine / Till leap year gives it twenty-nine. Alternate endings are: Which has eight and a score / Until leap year gives it one day more, or Which hath twenty-eight days clear / And twenty-nine in each leap year. or When ...

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Gregorian calendar, Gregorian calendar - History, Gregorian calendar - Invention, Gregorian calendar - Beginning of the year, Gregorian calendar - Adoption outside of Roman Catholic nations, Gregorian calendar - Proleptic Gregorian calendar, Gregorian calendar - Confusion with British vs. American usage, Gregorian calendar - Difference between Gregorian and Julian calendar dates, Gregorian calendar - Months of the year, Gregorian calendar - Accuracy, Gregorian calendar - Calendar seasonal error, Gregorian calendar - Numerical facts, Gregorian calendar - Number of leap years starting on a given day of the week, Gregorian calendar - Days of the week, Gregorian calendar - Reference

Read more here: » Gregorian calendar: Encyclopedia II - Gregorian calendar - Months of the year

This image shows the difference between the Gregorian calendar and the seasons. The Y axis is "days error" and the X axis is Gregorian calendar years. Each point represents a single date on a given year. The error shifts by about 1/4 day per year. Years that are multiples of 100 but not 400 are NOT leap years. This causes a correction on years 1700, 1800, 1900, 2100, 2200, and 2300. For instance, these corrections cause 23 December 1903 to be the latest December solstice, and 20 December 2096 to be the earliest solst ...

See also:

Gregorian calendar, Gregorian calendar - History, Gregorian calendar - Invention, Gregorian calendar - Beginning of the year, Gregorian calendar - Adoption outside of Roman Catholic nations, Gregorian calendar - Proleptic Gregorian calendar, Gregorian calendar - Confusion with British vs. American usage, Gregorian calendar - Difference between Gregorian and Julian calendar dates, Gregorian calendar - Months of the year, Gregorian calendar - Accuracy, Gregorian calendar - Calendar seasonal error, Gregorian calendar - Numerical facts, Gregorian calendar - Number of leap years starting on a given day of the week, Gregorian calendar - Days of the week, Gregorian calendar - Reference

Read more here: » Gregorian calendar: Encyclopedia II - Gregorian calendar - Calendar seasonal error