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The History of CalendarsWhat is a calendar? It is a way of measuring time. The main purpose of a calendar is to keep track of past and future time — to show how many days until a certain event takes place, as well as how many days have passed since a certain event occurred.
The earliest calendars were greatly influenced by the climates of the people who made them. We know this because, in colder climates, the concept of a year was determined by the seasons, specifically when winter ended. But in warmer climates, where the seasons are less dramatic, the moon became a way of measuring time.
Lunar calendars make up most of the oldest calendars, and base time on one moon to the next. A solar-year calendar was based on a 19-year period, with seven of those years having 13 months and the rest having 12 months. The period contained a total of 235 months. Lunar calendars were used by the ancient Chinese, Babylonians, Greeks, Jews, and Arabs.
The ancient Egyptians used a calendar with 12 months of 30 days, for a total of 360 days per year. To bring their calendar more in line with the solar year, in about 4,000 B.C., they added five extra days at the end of every year. The Egyptians figured that the solar year was 365 1/4 days, but instead of having a leap year every four years, they allowed the 1/4 days to accumulate. As the years passed, the months fell out of sync with the seasons, and the calendar year no longer coincided with the solar year.
Because of superstition about even numbers, the Roman Calendar had 29 or 31 days, except for 28-day February. Because their calendar added up to only 355 days, the Romans added an extra month of 22 or 23 days called Mercedonius, which was included every second year. While this was a good try, the Roman calendar was eventually so far off that Julius Caesar made the calendar year 445 days long, with a solar year of 365 days and six hours. To take care of the additional six hours, every fourth year was made into a 366-day year. Caesar can also be credited with beginning the calendar year in January.
While the Roman calendar was pretty good, it was 11 1/2 minutes too long, which did add up as the centuries passed. By the 15th century, the Roman calendar was about a week behind the solar calendar. In 1545, Pope Paul III was authorized to reform the calendar again. Thirty-seven years later, after much study and deliberation, Pope Gregory issued a Papal Bull to introduce the Gregorian calendar. This time, every fourth year was made a leap year, unless it was a century year that was not divisible by 400. While the Gregorian calendar used today is fairly accurate, it is still about 26 seconds longer than the Earth's orbital period.
Two Red Pins Mark Days on a Calendar
Online CalendarsClick on the calendar thumbnails below to display printable calendars for 2007, 2008, 2009, and 2010.
Visit the following online calendar websites to view and print calendars for the years 2007 A.D., 2008 A.D., 2009 A.D., 2010 A.D., 2011 A.D., 2012 A.D., 2013 A.D., 2014 A.D., and 2015 A.D., respectively, and to learn about each year's ten public holidays, as established by United States federal law.
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Printable Calendars - Calendar Guide