Calendar Origins

The answers to many questions about calendars

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Modern Calendar Origins:

Calendar Origins - Where did calendars begin?

Day Name Origins - Where did the Names of Days come from?

Calendar Name Origins - Where did the Names of Months come from?

Months of the Year Origin - Why 12 months in a year?

Why 28 days in February?

Who set the Year 0, AD, BC?

Calendars it Derived From:

Egyptian Calendar

Roman Calendar

Julian Calendar


Egyptian Calendar - Why 12 months in a year?

Ultimately, all calendars began with people recording time by using natural cycles: days, lunar cycles (months), and solar cycles (years).

The year is 365 days 5 hours 48 minutes 46 seconds long or 365.242199 days.

The time between full moons is 29.53 days.

The Ancient Egyptians are credited with the first calendar of 12 months, each consisting of 30 days, comprising a year. They added 5 days at the end of the year to syncronize somewhat with the solar year.

By making all their months an even 30 days, they abandoned trying to sync with lunar cycles and concentrated instead on aligning with the solar year.

The Egyptians recognized that this calendar didn't quite align with a actual year. They called the 1461 Egyptian years it took to re-align with the 1460 solar years a Sothis Period.

Eventually, the Greek rulers of Egypt under Ptolemy added the concept of a leap year, adding a day every 4 years. The Romans reinforced this concept when they later ruled Egypt.

 

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