History of Calendar and What is the Gregorian Calendar?

History of Calendar and What is the Gregorian Calendar?

When people first began to sow wheat and reap the harvest, they had observed that sowing falls each year at the same time. Then they tried to calculate how many days elapse between two successive sows.
This was the first attempt to determine how long one year is!
The ancient Egyptians were the first to accurately measure the length of the year. They knew that the best time for sowing is immediately after the Nile pours out of its bed, which happened every year. Their priests have noted that between two such consecutive floods new moon appeared twelve times. So they counted twelve “months” and now they were able to calculate when the River Nile will pour out of its bed.
However, still this was not enough accurate.
Then the Egyptian priests noticed that every year, around the time of the flood, one bright star appears in the sky just before sunrise. They counted the days until it happened again, and they found that 365 days had passed.  This was 6,000 years ago, and before that, nobody knew that a year has 365 days!
Egyptians divided the year into 12 months, each month in 30 days and 5 days remained to the end of the year. So they invented the first calendar.
Later, the calendar was not based on the moon anymore (lunar calendar), but on the number of days (365 and 1/4) required for the Earth to revolve around the sun (solar calendar). This one quarter of the day (1/4) was creating an increasing confusion.

Finally in the time of Julius Caesar, this was put in order.

Julius Caesar determined that 46 BC would last five days , in order to “catch up”, and the next years since then will have 365 days, except every fourth – which would be a leap and will have 366 days, and will thus benefit from parts remaining from the three remaining years .
However, in time it turned out that Easter and other holidays do not fall into that time of the year to which they belong. To many “redundant” days piled up and therefore, in 1582 the Pope Gregory XIII ruled that the year 1582 would be shortened for ten days.
But for the calendar to be accurate in future, Pope Gregory XIII decided to skip the leap year every last year of the century, except if the year is divisible by 400.
There for 1700, 1800 and 1900 were not leap years, but year 2000 was!

This system is called the Gregorian (new) calendar, and is now used throughout the world, although some denominations still use their calendars for religious purposes.

Inscription on the grave of Gregory XIII, St. Peter’s Basilica, Gregorian Calendar
Source: Wikipedia

Origin of Days of the Week

The week is “artificial” division of time. One “day” is determined by the rotation of the Earth around its axis, and the year is the time needed for the Earth to revolve around the sun. However, the week was actually invented.
Before the creation of the week, the only division of time was on months. This division was based on the phases of the moon.
The days didn’t have names.
However, when people began to build bigger cities, they wanted to have special days for trade.
Such “Days of Commerce” were sometimes every tenth day, sometimes every seventh or one in five. Babylonians, for example, had every seventh day for trading. On this day they did not work, unless they gathered for trade or religious ceremonies. The Jews followed their example, and they kept the seventh day kept exclusively for religious purposes.
This created the “week”. Week is simply represented as the time period between the days of the trade. Thereafter, it was just to give names to individual days. Jews simply enumerated the days of the week , counting from the Sabbath, or Saturday. Wednesday for example, was the fourth day after the Sabbath.
In the old days, many people also had a week, but it not always had seven days. The Greeks, for example, began with a ten-day week. Later they adopted the seven – day week, which was in force in the Egyptian city of Alexandria. The Romans had the first week of eight days and it was not until the fourth century, when the seven-day week was introduced.