I always get a bunch of calendars from my credit union, my insurance guy, the NEA, and several other people. I usually end up purchasing a few filled with beautiful pictures. My mother commented the other day that she has not yet gotten the calendar from her bank. It might be because she just moved.
Early societies didn't have the same type of calendar we use today. They used observations of the stars throughout the year to predict upcoming events.
The Babylonians created a simple lunar calendar but it did not match up with the actual length of the real year. Each lunar month is only 29.5 days so at the end of the lunar year, its only accounted for 354 days. The calendar is about 11 days short so every year, the months shift in relation to the natural year and matches up every 32 years.
The Egyptians also used a lunar calendar but they were aware that the year was actually 365 days so they made months 30 days long and added 5 extra days at the end of the year to get it to balance out. This calendar still ended up short by one day, every four years. They did not make any adjustments and their calendar slowly moved backwards returning to its original point every 1460 years.
The use of lunar calendars continued till the first century when Rome began making changes. By the time Julius Caesar came into power, the calendar was at least three months off of the seasons. So the leading astronomer of the time recommended they add 90 days to the year and begin the new calendar on January 1, 45 BC. They based the new calendar on 365 day 6 hour long solar year. This was approx. 12 minutes off so it took 130 years to become one day off.
At about the same time Julius Caesar developed his calendar, the Mayans created their own calendar made up of 18 months with 20 days in each month but they had to add 5 days at the end of the year to even it out. People believed these extra 5 days were unlucky.
The next major calendar began in 1582 when they added 10 days to the calendar going from October 5th to October 15th immediately. Pope Gregory's astronomers came up with the idea that if the number of year is divisible by 4, then it had an extra day and the year became known as leap year. 2018 is not a leap year but 2020 is. Not every country jumped on with the new calendar. It took Great Britain till 1752 to adopt the new one but by then, they were 11 days off of those who used the Gregorian Calendar. Russia never changed over until the revolution in 1918 which made for confusing dates and such.
I hope you enjoyed the brief history of calendars. I hope you learned something because I did. Have a great day.