How The Calendar Began?
When people began to plant seeds and harvest crops, they noticed that the sowing time came at regular intervals every year. They tried to count days that elapsed between one planting and the next. This was a maiden attempt by man to arrive at how long a year was.
With a certain degree of exactness, the ancient Egyptian measured a year. For them, the best time to plant was after the Nile River overflowed each year. The priests noticed that between each overflowing the moon rose 12 times. They counted 12 months or 1 month and figured out when the wide world rise again.
It was not adequately exact. The priests in Egypt noticed about the time of the floods a bright star would rise before the sun, rose. They counted the days that passed before this happened again and found that it added up to 365 days. This was 6000 years ago and earlier than that nobody knew that there were 365 days in a year. The Egyptians divided the year into 12- months of 30 days each, with 5 extra days at the end of the year. Thus they invented the first calendar.
Eventually, the calendar was not based on this moon (lunar calendar), but on the number of days (365/1 /4) it takes the earth to go around the sun (solar calendar). The extra one-quarter began to cause confusion. Finally, Julius Caesar decided to straighten it all. He decided 445 days in the year 46 BC and every year from then onwards was to have 365 days, except every fourth year. The fourth-year would be a leap year of 366 days and thus use up the fraction.
With the time rolling by it was discovered that Easter and other holy days were not coming where they belonged in the season. Too many extra days piled up. It was in the year 1582 that Pope Gregory XIII decided to do something about it and ordered to drop ten days from the year. It was done to keep the Calendar accurate for all times to come. He also ordered that the leap year be skipped over in the last year of every century unless that year could be divided by 400. Thus 1700, 1800, 1900 were not leaped years but the year 2000 will be a leap year.
This system is called Gregorian Calendar and is now used all over the world for everyday purposes though various religions still use their own Calendar for religious purposes.