Gregorian and the Julian Calendar Systems

Gregorian and the Julian Calendar Systems

There are very few things in life that we know for sure will happen. One of those things is that every year, the calendar starts over with January 1 and has 365 days…with the exception of an added day every four years.

Do you know the history of the calendar system that we use? Did you know that there is a difference in the calendar we use today versus the calendar used just a few centuries ago?

Julian Calendar

The Julian Calendar was established in 45 BC under Roman dictator, Julius Caesar. It was developed to create consistency in the calendar year and the changing of each season.

One major change was adjusting the year to start on January 1. Previously, the calendar year had started in March.

Prior to the Julian calendar, years had less days and often implemented leap year days which were becoming inconsistent and caused an imbalance of the calendar month compared to present season.

Gregorian Calendar

The Gregorian Calendar is what we use today.

This was established in 1582 and adopted by Pope Gregory XIII. The Gregorian calendar is a refined version of the Julian Calendar to be more approximate with the equinoxes and solstices. Without the corrections made in this calendar, it was realized that in the Julian Calendar the calendar would 10 days behind the spring equinox in 1582.

This calendar system became the international standard but took a few centuries for countries around the world to adopt. It was first adopted in Spain, Portugal, Italy and France in 1582. Great Britain and the American colonies adopted it in 1752. The last country to adopt the new calendar was Turkey in 1926.

Leap Year Explained

When the calendars were configured, actual days do not come out to an even 365.

  • Julian – 365.25 days
  • Gregorian – 365.2425 days

Leap year is the term given for the time added to the calendar to make up for time lost to keep consistency with the months and the seasons based on the earth’s rotation with the sun.

To make up for the lost time in each calendar, an extra day is added to the calendar every four years.

If this extra day isn’t added, we’d lose 6 hours a year to our calendar. (6 hours a year x 4 = 24 hours). Over time, the seasons would become off. For example, we could be celebrating the 4th of July during the winter season.

Fun Fact: The next leap year will be February 29, 2020.

How Does this Affect Genealogy Research?

Because the Gregorian system was established in 1582 but took a couple of centuries for most countries to adopt, dual dating (or sometimes referred to as double dating) was used on documents to give the date according to both systems during the changeover or where applicable.

If you are looking at records from a country that hadn’t yet adopted the Gregorian system or was in the process of changing, you might see dual dating on documents. This can be confusing if it’s not obvious that this is what they were doing or if you are unfamiliar with dual dating.

You could also see old documents that don’t have accurate dates or dates that have been adjusted over time. For example, this article from the National Archives explains a change to George Washington’s birthday. George Washington’s original birthday was on February 11, 1731. With Great Britain adopting the new calendar system, his birthday was adjusted to February 22, 1732.

The history of these calendars is quite interesting and this blog article only scratches the surface on everything involved with these two calendar systems.

If you have come across a document that might have dual dating and you weren’t sure what was, you may want to check out this reference on how to handle that date so you can accurately record that in your family tree.