Origin of calendar dating
The Gregorian Calendar uses a much more accurate rule for calculating leap years.
To get the calendar back in sync with astronomical events like the vernal equinox or the winter solstice, a number of days were dropped.
Julius Caesar invited astronomer Sosigenes of Alexandria to advise him about the reform of the calendar, and Sosigenes decided that the only practical step was to abandon the lunar calendar altogether. Pope Eastern Orthodox churches continue to use the Julian calendar for determining fixed liturgical dates; others have used the Revised Julian calendar, which closely resembles the Gregorian calendar, since 1923 for such dates.
Sosigenes had overestimated the length of the year by 11 minutes 14 seconds, and by the mid-1500s the cumulative effect of this error had shifted the dates of the seasons by about 10 days from Caesar’s time.
This increased the year's length to 354 or 355 days.
The addition of January and February meant that some of the months' names no longer agreed with their position in the calendar (September - December).
Each day was referred to by how many days it fell before the .
For example, March 11 would be known as “Five Ides” to the Romans because it is four days before the Ides of March (March 15).
An extra month was added to the calendar in some years to make up for the lack of days in a year.The 304-day Roman calendar didn’t work for long because it didn’t align with the seasons.King Numa Pompilius reformed the calendar around 700 BCE by shortening the 30-day months to 29 days and adding the 29-day month of January (Ianuarius) and the 28-day month of February (Februarius) to the original 10 months.The delay in switching meant that different countries not only followed different calendars for a number of years but also had different rules to calculate whether a year was a leap year.This explains why the years 1700, 18 were leap years in countries still using the Julian calendar (e.g.
These 3 markers were called occurred on the 15th day of March, May, July, and October, and the 13th day of the other months.