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Calendars and Dates

In 46 B.C., Julius Caesar decreed a calendar with 365 days divided into 12 months to be used in Rome. The calendar introduced a leap day every four years to account for those extra quarter days it takes to circle the sun. And it would have been a good calendar if a year real were 365.25 days long, but a year is 365.24 days long. So the Julian calendar added too many leap years. By the 14th century, the spring equinox had slipped 10 days to March 11 instead of March 21. That threw off the date of Easter, which falls on the Sunday after the first full moon after the spring equinox.

In 1582, Pope Gregory XIII convened a panel to fix the calendar. Because the Julian calendar was so far ahead  of the season, 10 days were chopped out of October, so October 4, 1582, was followed by October 15, 1582. To prevent the calendar from getting ahead of itself again, the scientists proposed to hobble some of the leaps. Now leap years occur in years divisible by 4, except for years ending in 00. If a century is divisible by 400, it is a leap year. So 2000 was a leap year, but 2100 will not be a leap year. The Gregorian calendar also established January 1 as the start of the year. The change was quickly implemented by Catholic countries, but rejected in Protestant regions. It was gradually accepted by most of Europe between 1699 and 1701.

England, Ireland and the American colonies didn't start using the Gregorian calendar until 1752. By that time, the Julian calendar had slipped another day, so 11 days had to be cut out of September 1752 to compensate. Confusion is sometimes encountered when attempting to calculate a pre-1752 birth date based on a post-1752 age at death.

  • Birthdate Calculator.  Site that calculates a birth date from a death date and age at death in years, months, and days.
  • Birthdate Calculator. Calculates birth date from death date and age of death in year-month-day format. All dates according to the Gregorian calendar, with New Year on Jan. 1. Olive Tree Genealogy.
  • Birth Date Calculator  Calculates birth date from tombstone, death certificate or obituary and age at death. Gives results in a year-month-day format.
  • Birth Date Calculator. Calculate birth dates from the death date and age at the time of death. ProGenealogists.
  • Bukke, Inger et. al. The Comprehensive Feast Day Calendar. Bountiful, Utah: Thomsen's Genealogical Center, 1983.
  • Calculate Birthdate from Death Data. Calculates birth date from death date and age of death in year-month-day format. All dates according to the Gregorian calendar, with New Year on Jan. 1.
  • Calculating Birth Year Based on Census Information. Charts that convert ages in the federal censuses, 1790-1920, into approximate birth years.
  • Calculation of the Ecclesiastical Calendar. Marcos J. Montes. Use this to find the dates for feast date references.
  • Calendar From George G. Morgan. An excellent perpetual calendar resource, with 10,000 year calendar website. Here you can select a century, a year, and a month, and click to display a calendar.
  • Calendar Zone
  • Calendars - An interesting history of how calendars came to be and how we tried to organize our lives in accordance with the movement of the sun, moon and stars.
  • Calendars and Their History.  L.E. Doggett.
  • Dates of Easter Sunday and Perpetual Calendar, 1550-2049 for Great Britain and the Colonies. Brian Pears.
  • Day of the Week Calculator. From Ancestor Search.
  • Duncan, David Ewing. Calendar: Humanity's Epic Struggle to Determine a True and Accurate Year. New York: Avon, 1998.
  • European Calendar and Feast Days
  • Morse, Stephen P. "The Jewish Calendar Explained: An Expert Tells a Tale." Association of Professional Genealogists Quarterly 22, 3 (September 2007): 125-134.
  • Old Style and New Style Dates and the Changes to the Gregorian Calendar. Mike Spathaky. A summary for genealogists.
  • Regnal Chronologies. Bruce R. Gordon. Information about the study of royal chronologies, king lists, and governances, and the organization of such.
  • Richards, E.G. Mapping Time: The Calendar and Its History. Oxford, England: Oxford University Press, 1999.
  • Rosetta Calendar. Scott Lee. A calendar conversion service. Show the same date in Gregorian, Julian, and Hebrew date format.
  • Smith, Gary M. and Diana Crisman Smith. "Dates and Calendars." NGS NewsMagazine 33, 1 (January/February/March 2007): 41-43.
  • Smith, Kenneth L. Genealogical Dates: A User Friendly Guide. Camden, Maine: Picton Press, 1994.
  • The 10,000 Year Calendar.
  • Time and Date. It allows you to put in any year and select from a list of countries, as well as Gregorian and Julian calendar options. You can also customize the calendars with holidays and observances, even the phases of the moon.
  • Ultimate Calendar Web Page
  • Western-Chinese Calendar Converter. Includes links to other sites with information on the Chinese solar calendar and converters for Western to Chinese calendars.