Julian calendar facts for kids

The Tusculum portrait of Julius Caesar

The Julian calendar is a way to organize time, like the calendar we use today. It has 365 days in most years, but every four years, it adds an extra day, called a leap day. This calendar was created by Julius Caesar in 46 BC to fix problems with the old Roman calendar. It started on 1 January 45 BC.

For over 1,600 years, the Julian calendar was the main calendar used in the Roman Empire and much of the Western world. Later, in 1582, Pope Gregory XIII introduced a new calendar, called the Gregorian calendar, which is what most of the world uses now.

Today, the Julian calendar is still used by some parts of the Eastern Orthodox Church and Oriental Orthodox Churches for religious holidays. It is also used by the Amazigh people (also known as Berbers). If you want to compare dates between 1901 and 2099, a Julian date is 13 days behind a Gregorian date. For example, Julian 1 January is Gregorian 14 January.

Months of the Julian Calendar

How the Julian Calendar Started

Why a New Calendar Was Needed

Before Julius Caesar, the old Roman calendar had 355 days. Sometimes, an extra month called Mensis Intercalaris was added between February and March. This was supposed to keep the calendar in line with the seasons.

However, the people in charge of adding this extra month, called pontifices, were often politicians. They could make a year longer or shorter to help their friends or hurt their enemies in office. This caused a lot of confusion and made the calendar unreliable.

Julius Caesar wanted to fix this problem for good. He aimed to create a calendar that would always stay aligned with the sun, without anyone needing to interfere. This new calendar brought much-needed stability to dating events and seasons.

The Idea Behind the Reform

People had known for a long time that a year was about 365 and a quarter days long. But older calendars weren't always that accurate, so they slowly drifted out of sync with the seasons.

Caesar likely saw this problem firsthand in Egypt, which used a 365-day calendar that also drifted. He spent time there in 48 BC and saw how their calendar worked.

When Caesar returned to Rome in 46 BC, he gathered smart people, including the astronomer Sosigenes of Alexandria. Together, they designed a new calendar. It combined ideas from the old Roman months, the fixed length of the Egyptian calendar, and Greek astronomy's understanding of the year's length.

How the Julian Calendar Spread

Caesar's new calendar was first used in Rome. Over the next few decades, many other calendars in the Roman Empire and nearby kingdoms changed to match the Julian system. They adopted the 365-day year with a leap day every four years.

Even though these local calendars kept some of their old traditions, like different New Year's Days or month names, they now had a clear connection to the Julian calendar. This made it much easier to convert dates between different regions.

How Caesar Changed the Calendar

Making the Year Match the Seasons

To start the new Julian calendar correctly, Caesar had to fix the old calendar first. The year 46 BC was made extra long, with 445 days! This was done to catch up for all the missed adjustments in previous years.

This super-long year was called the "last year of confusion." After this big adjustment, the new Julian calendar officially began on 1 January 45 BC.

How Months Were Changed

The Julian calendar took the old Roman year of 355 days and added ten days to make it 365 days long.

• January, August (Sextilis), and December each gained two extra days.
• April, June, September, and November each gained one extra day.
• February kept its 28 days in a normal year.

This way, the months ended up with the same number of days we have today (except for February in a leap year). The way Romans counted days within a month (using Kalends, Nones, and Ides) stayed the same.

Adding the Leap Day

The old system of adding an entire extra month was stopped. Instead, a single leap day was added every four years. This extra day was placed in February.

In the Roman calendar, this leap day was called ante diem bis sextum Kalendas Martias, which means "the sixth doubled day before the Kalends of March." This is why we sometimes call a leap year a "bissextile year." For most purposes, this extra day became the day before February 25th.

Understanding the Year's Length

The Julian calendar has two kinds of years: a "normal" year with 365 days and a "leap" year with 366 days. It follows a simple pattern: three normal years, then one leap year, and this repeats forever.

This means the average length of a Julian year is 365.25 days. However, the actual solar year (the time it takes for Earth to orbit the sun) is slightly shorter, about 365.2422 days. This small difference meant that the Julian calendar slowly gained about one day every 129 years. Over many centuries, this caused the calendar to drift out of sync with the seasons.

Early Mistakes with Leap Years

Even though Caesar designed a clear system, the priests who managed the calendar made a mistake at first. Instead of adding a leap day every four years, they added one every three years. This meant too many leap days were added over time.

About 36 years later, the Roman Emperor Augustus noticed this error. To fix it, he ordered that no leap days should be added for 12 years. This corrected the calendar, and after that, the Julian calendar followed Caesar's original plan of a leap year every four years.

Month Names and Their Changes

Roman Month Names

The Julian calendar didn't immediately change month names. However, Romans later renamed two months to honor important leaders.

• The month of Quintilis was renamed Iulius (July) in 44 BC, to honor Julius Caesar, as it was his birth month.
• The month of Sextilis was renamed Augustus (August) in 8 BC, to honor Emperor Augustus. Many important events in his life happened during this month.

Other Roman emperors tried to rename months after themselves, like Caligula or Nero. But these changes usually didn't last beyond their reigns.

Other Historical Month Names

A long time after the Roman Empire, Charlemagne, a powerful ruler in Europe, gave new names to the months. These names were based on farming activities and the seasons in Old High German. For example, January was "winter month" (Wintarmanoth), and July was "hay month" (Heuuimanoth). These names were used for hundreds of years.

In Eastern Europe, many countries kept older, seasonal names for their months, even into the 19th century. Some of these traditional names are still used today in languages like Polish, Ukrainian, and Croatian.

How Years Were Counted

Counting Years in Ancient Rome

In ancient Rome, people usually identified a year by naming the two consuls who were in charge during that year. This was like saying "the year of Consul A and Consul B." From 153 BC onwards, these consuls started their term on 1 January, matching the calendar year.

Romans also sometimes counted years from the founding of their city, known as ab urbe condita (AUC). Historians used this method to track time between events. The most common starting point for AUC was 753 BC.

The Anno Domini System

Later, a new system for numbering years was created in 525 AD by Dionysius Exiguus. This system, called Anno Domini (AD), counts years from the supposed birth of Jesus Christ. It slowly became popular across Europe, especially after the historian Bede used it in the 8th century. This is the system we mostly use today (often called CE for Common Era).

Other Ways to Count Years

Different regions and groups also had their own ways of numbering years. For example, Christians in Alexandria used the "Era of Martyrs," starting from the reign of Emperor Diocletian. In the Byzantine Empire, they used an Anno Mundi system, which counted years from the creation of the world according to the Bible.

The Berbers in North Africa, who still use a form of the Julian calendar, have adopted an era starting in 950 BC. This marks the time when the Libyan pharaoh Sheshonq I came to power in Egypt.

When the New Year Began

The Roman calendar, and later the Julian calendar, always started the year on 1 January. However, in different places and at different times, people using the Julian calendar celebrated New Year's Day on other dates.

• In Egypt, the Alexandrian calendar started on 29 August.
• Some Roman provinces started their year on 23 September, which was Emperor Augustus's birthday.
• The Byzantine Empire started its year on 1 September. This date is still used by the Eastern Orthodox Church for the start of its religious year.
• In early England, the year often began on 25 December (around the winter solstice) or 25 March (the equinox). England officially moved its New Year's Day to 1 January in 1752.

Because of these different starting dates, sometimes people would write dates like "1661/62" to show if they meant the year starting in March (1661) or January (1662).

When Countries Adopted January 1st as New Year's Day

The Julian Calendar is Replaced

Why the Gregorian Calendar Was Created

By 1582, the Julian calendar had drifted significantly. Because the Julian year was a little longer than the actual solar year, the calendar gained about one day every 128 years. This meant that the date of the March equinox, which is important for calculating Easter, was ten days off from where it should have been.

To fix this, Pope Gregory XIII introduced the Gregorian calendar in 1582. This new calendar made small changes to the leap year rule to make it much more accurate. It gained only about 0.1 day over 400 years, making it much closer to the true length of the solar year.

Switching to the New Calendar

Most Catholic countries quickly adopted the Gregorian calendar in 1582. Protestant countries and many Eastern Orthodox countries switched much later. Greece, for example, was one of the last to adopt it for civil use in 1923.

When countries switched calendars, it caused some confusion. To make things clear, people sometimes used "dual dating" in documents, showing the date in both the old Julian calendar (called "Old Style" or O.S.) and the new Gregorian calendar (called "New Style" or N.S.).

For example, the famous October Revolution in Russia happened on 25 October according to the Julian calendar (O.S.). But by the Gregorian calendar (N.S.), it was 7 November 1917.

Calendars Similar to Julian Today

The Ethiopian calendar is based on a calendar similar to the Julian one, called the Alexandrian calendar. Ethiopia still uses it as its official civil calendar.

Who Still Uses the Julian Calendar Today?

Eastern Orthodox Churches

Many Eastern Orthodox countries adopted the Gregorian calendar for everyday life. However, most of their churches still use the Julian calendar for religious holidays.

This means that holidays like Christmas are celebrated on different dates than in Western churches. For example, Christmas on 25 December in the Julian calendar falls on 7 January in the Gregorian calendar (this will be true until the year 2100).

All Orthodox churches, except for the Finnish Orthodox Church, continue to calculate the date of Easter using the Julian calendar. This means Easter is celebrated on the same day by most Orthodox Christians around the world.

Other Groups Using the Julian Calendar

• Syriac Christianity: The Ancient Assyrian Church of the East celebrates Christmas on 7 January (Gregorian), which is 25 December in the Julian calendar.
• Oriental Orthodox: The Armenian Patriarchate of Jerusalem still uses the Julian calendar, while other parts of the Armenian Church use the Gregorian calendar.
• Berbers: The Amazigh people (Berbers) in North Africa use a form of the Julian calendar for their traditional Berber calendar.
• Foula, Scotland: On the small island of Foula in Shetland, Scotland, people still celebrate some festivals according to the Julian calendar.

See also

In Spanish: Calendario juliano para niños

• Byzantine calendar
• Conversion between Julian and Gregorian calendars
• Julian day
• Julian year (astronomy)
• List of adoption dates of the Gregorian calendar per country
• Mixed-style date
• Old New Year
• Proleptic Gregorian calendar
• Proleptic Julian calendar
• Revised Julian calendar
• Roman timekeeping
• Week