Julian calendar facts for kids

The Julian calendar is a solar calendar that has 365 days in most years. Every fourth year, it adds an extra day, called a leap day, making that year 366 days long. This calendar is named after Julius Caesar, who introduced it in 45 BC. It was the main calendar used in the Roman Empire and much of the Western world for over 1,600 years.

Even today, the Julian calendar is still used for religious purposes by some parts of the Eastern Orthodox Church and Oriental Orthodoxy. It is also used by the Amazigh people, sometimes known as Berbers.

The Julian calendar has an average year length of 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 means the Julian calendar gains about one day every 129 years. This slow drift led to a new calendar being created. In 1582, Pope Gregory XIII introduced the Gregorian calendar, which is the calendar most of the world uses today.

How the Julian Calendar Works

The Julian calendar has two types of years:

• A normal year with 365 days.
• A leap year with 366 days.

Leap years happen every four years without any exceptions. This simple rule made the calendar much easier to use than the older Roman calendar.

Why a New Calendar Was Needed

The old Roman calendar was quite complicated. It had 12 months, totaling 355 days. Sometimes, an extra month called Mensis Intercalaris was added between February and March. This extra month was supposed to keep the calendar aligned with the seasons.

However, the decision to add this extra month was made by priests called pontifices. These priests were often politicians. They could make a year longer or shorter, which sometimes caused problems. For example, they might lengthen a year if their friends were in power, or shorten it if their rivals were.

Julius Caesar wanted to fix this problem. He wanted a calendar that would stay aligned with the sun without anyone needing to interfere. This new calendar made it much easier to track the seasons and important dates.

The Year of Confusion

To start the new calendar correctly, the year 46 BC had to be made extra long. It was 445 days long! This was done to catch up and realign the calendar with the seasons. People called it the "last year of confusion." The new, regular Julian calendar officially began on 1 January 45 BC.

Month Lengths

The Julian calendar set the lengths of the months to what they are mostly today. Ten days were added to the old 355-day Roman year to make it 365 days.

• January, August, and December each gained two extra days.
• April, June, September, and November each gained one extra day.
• February stayed at 28 days in normal years. In a leap year, February gained the extra day, making it 29 days long.

The way Romans counted days within a month (using Kalends, Nones, and Ides) did not change.

Leap Day Rule

The old extra month was removed. Instead, a single leap day was added in February. This leap day was called the bissextile day. It was inserted after February 23rd. So, in a leap year, February 24th was effectively doubled.

Early Leap Year Mistakes

Even though Caesar made the calendar simpler, the priests initially made a mistake. They added a leap day every three years instead of every four. This error continued for 36 years, adding too many leap days.

When the mistake was finally noticed, Augustus, the first Roman emperor, corrected it. He ordered that no leap days should be added for 12 years. After this correction, the calendar followed Caesar's original plan, with a leap year every four years.

Month Names

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

• Quintilis was renamed Iulius (July) in 44 BC to honor Julius Caesar, as it was his birth month.
• Sextilis was renamed Augustus (August) in 8 BC to honor Emperor Augustus, because many important events in his life happened in that month.

Other emperors tried to rename months after themselves, but these changes usually didn't last after they died.

Other Month Names

Over time, different cultures adopted the Julian calendar but used their own month names.

• In Charlemagne's time (around 800 AD), Old High German names were introduced, often related to farming activities. For example, "Wintarmanoth" (winter month) for January. These names were used for centuries.
• In Eastern Europe, many languages still use older, seasonal month names that are different from the Latin-derived names common in Western Europe.

How Years Were Counted

Romans usually identified years by naming the two consuls who were in office that year. This was called the "consular year." From 153 BC, consuls started their term on January 1st, matching the calendar year.

Sometimes, Romans also numbered years from the founding of the city (ab urbe condita or AUC). However, this was mainly used by historians, not for everyday dating. Different historians had slightly different dates for Rome's founding. The date 753 BC is commonly used by modern historians.

Later, in 525 AD, a monk named Dionysius Exiguus created the system we use today: Anno Domini (AD), meaning "in the year of the Lord." This system gradually spread across Europe, especially after it was adopted by the historian Bede in the 8th century.

New Year's Day

The Roman calendar always started the year on January 1st, and this continued with the Julian calendar. However, when other regions adopted the Julian calendar, they sometimes kept their traditional New Year's Day.

• The Alexandrian calendar in Egypt started on August 29th.
• In the Byzantine Empire, the year began on September 1st. This date is still used by the Eastern Orthodox Church for the start of its religious year.
• In England, the year often began on December 25th or March 25th for a long time. It wasn't until 1752 that England officially moved New Year's Day to January 1st.

Why the Gregorian Calendar Replaced It

The Gregorian calendar gradually replaced the Julian calendar as the main calendar in most countries. This change was needed because the Julian calendar was not perfectly accurate.

The Julian year, at 365.25 days, was slightly longer than the actual solar year. This meant that over centuries, the calendar slowly drifted out of sync with the seasons. By 1582, the date of the March equinox (around March 21st), which is important for calculating Easter, was about 10 days off from where it should have been.

To fix this, Pope Gregory XIII introduced the Gregorian calendar in 1582. This new calendar adjusted the leap year rule: years evenly divisible by 100 are NOT leap years, unless they are also evenly divisible by 400. This small change made the calendar much more accurate, gaining only about 0.1 day over 400 years.

During the time when both calendars were in use, people sometimes used "O.S." (Old Style) for Julian dates and "N.S." (New Style) for Gregorian dates to avoid confusion. For example, the October Revolution in Russia happened on October 25th O.S., but on November 7th N.S.

Modern Usage

Even though most of the world uses the Gregorian calendar, the Julian calendar is still important:

Eastern Orthodox Churches

Many Eastern Orthodox churches still use the Julian calendar for their religious holidays. This means they celebrate Christmas on December 25th according to the Julian calendar, which currently falls on January 7th in the Gregorian calendar. They also use the Julian calendar to calculate the date of Easter.

Other Groups

• The Ancient Assyrian Church of the East also uses the Julian calendar.
• The Armenian Patriarchate of Jerusalem uses the Julian calendar, while other parts of the Armenian Church use the Gregorian.
• The Berbers in North Africa still use the Julian calendar for their traditional Berber calendar.
• On the small island of Foula in Scotland, people still celebrate some holidays 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