The Measuring of Time: A History of the Calendar

Marcelo Serafim
5 days ago
6 min read

For millennia, humanity has looked to the heavens to organize life on Earth. The earliest calendars were likely lunar, based on the cycles of the moon's phases. While the moon provided an easy visual tracker for the passage of time, a purely lunar year (roughly 354 days) falls out of sync with the solar year (approximately 365.24 days) and the seasons. This discrepancy posed significant challenges for early agricultural societies that relied on predicting seasonal changes for planting and harvesting. To solve this, ancient civilizations like the Egyptians began prioritizing the solar cycle, noting that the annual flooding of the Nile coincided with the heliacal rising of the star Sirius.

By the time of the Roman Republic, the calendar was a chaotic mix of lunar and solar elements. The Roman calendar originally consisted of ten months and 304 days, with winter existing as an uncounted gap in time. Eventually, two more months, January and February, were added, but the system remained flawed. The pontiffs, who managed the calendar, would often add "intercalary" days arbitrarily to realign the months with the seasons, or sometimes for political reasons to extend the terms of office for their allies. By the first century BCE, the Roman calendar was effectively broken, drifting months away from the actual seasons.

In 46 BCE, Julius Caesar, advised by the astronomer Sosigenes of Alexandria, initiated a massive reform. He introduced the Julian calendar, a solar calendar that abandoned lunar cycles entirely. Caesar established a year of 365 days and introduced the concept of the "leap year." Every four years, an extra day would be added to February to account for the fact that the Earth takes roughly 365.25 days to orbit the sun. To align the new calendar with the seasons, the year 46 BCE was extended to 445 days, earning it the nickname the "Year of Confusion."

While the Julian calendar was a vast improvement, it was not perfect. The actual solar year is 365.24219 days, not 365.25. This minor difference—about 11 minutes per year—might seem negligible, but over centuries, it accumulated. By the 16th century, the calendar had drifted by about ten days. This drift was particularly problematic for the Catholic Church because it affected the calculation of Easter, the most important Christian holiday, which is tied to the spring equinox.

The connection between our calendar and the birth of Jesus Christ was established much later than Caesar's time. In the 6th century AD, a monk named Dionysius Exiguus (Dennis the Small) was working on calculating the dates for Easter. At the time, years were often numbered based on the reign of the Roman Emperor Diocletian. Dionysius, wishing to stop honoring a persecutor of Christians, decided to number the years starting from the incarnation of Jesus. He designated the year of Jesus' birth as "1 AD" (Anno Domini, or "In the year of the Lord").

However, scholars today believe Dionysius likely miscalculated. Based on historical references in the Gospels—such as the reign of King Herod the Great, who died in 4 BC—Jesus was likely born between 6 BC and 4 BC. Despite this probable error, Dionysius's system eventually became the standard for the Christian world. It divided history into two eras: BC (Before Christ) and AD (Anno Domini). It is important to note that there is no "Year Zero" in this system; the calendar moves directly from 1 BC to 1 AD.

By 1582, the 11-minute error in the Julian calendar had caused the spring equinox to drift from March 21st to March 11th. Pope Gregory XIII commissioned a reform to correct this. His solution, developed by astronomer Aloysius Lilius, resulted in the Gregorian calendar. To stop the drift, the new system kept the leap year rule but added an exception: century years (like 1700, 1800, 1900) would not be leap years unless they were divisible by 400. Thus, 1600 and 2000 were leap years, but 1900 was not.

To reset the calendar, Pope Gregory also took drastic action: he deleted ten days from October 1582. People went to sleep on October 4th and woke up on October 15th. This change was initially adopted only by Catholic countries. Protestant and Orthodox nations viewed the new calendar with suspicion, seeing it as a "Papal plot." For centuries, Europe operated on two different times; a traveler could cross a border and essentially travel ten (and later eleven) days backward or forward in time.

Great Britain and its American colonies did not adopt the Gregorian calendar until 1752. By then, the discrepancy had grown to 11 days. When the shift finally happened, it caused significant confusion and even sparked riots, with people reportedly demanding, "Give us back our eleven days!" Eventually, globalization and the need for a standardized system for trade and communication forced the rest of the world to conform. Russia adopted it after the 1918 revolution, and Greece followed in 1923.

Today, the Gregorian calendar is the internationally accepted civil calendar. While many cultures maintain their own religious or traditional calendars (such as the Hebrew, Islamic, or Chinese calendars), the Gregorian system facilitates global commerce and travel. In recent decades, the terms BCE (Before Common Era) and CE (Common Era) have gained popularity in academic and scientific circles as a culturally neutral alternative to BC and AD, though the numbering remains exactly the same, tethered to Dionysius’s ancient calculation.

Comprehension Questions

Why was the Julian calendar nicknamed the "Year of Confusion" when it was first implemented?
What was the specific mathematical error in the Julian calendar that caused the "drift" over centuries?
Who was Dionysius Exiguus, and what significant change did he introduce to the way years were numbered?
Why are the years 1700, 1800, and 1900 not considered leap years in the Gregorian calendar, while 2000 is?
Why did Protestant and Orthodox countries initially refuse to adopt the Gregorian calendar?

Vocabulary

Heliacal (adj.): Relating to the rising of a star just before the sun; used in astronomy.
Discrepancy (n.): A lack of compatibility or similarity between two or more facts.
Intercalary (adj.): (Of a day or a month) inserted in the calendar to harmonize it with the solar year.
Negligible (adj.): So small or unimportant as to be not worth considering; insignificant.
Accumulated (v.): Gathered together or acquired an increasing number or quantity of something.
Incarnation (n.): A person who embodies in the flesh a deity, spirit, or abstract quality (in this context, the birth of Jesus).
Commissioned (v.): Ordered or authorized someone to do or produce something.
Drastic (adj.): Likely to have a strong or far-reaching effect; radical and extreme.
Conform (v.): Comply with rules, standards, or laws.
Tethered (v.): Tied to; chemically or physically connected or related to.

Phrasal Verb

Phrasal Verb: Date back to

Meaning: To have existed since a specific time in the past; to have a particular origin.
Examples:
- "The tradition of lighting fireworks on New Year's Eve dates back to ancient China."
- "Some of the documents we found in the library date back to the 12th century."

American Idiom

Idiom: Make up for lost time

Meaning: To do something faster or more often in order to compensate for not having done it earlier.
Context: This relates to the text where Pope Gregory removed days from the calendar to "make up" for the drift caused by the Julian error.
Example: "After being sick for a week and missing school, Sarah had to study all weekend to make up for lost time."

Grammar Tip: Passive Voice in History

When writing about history or scientific processes, we often focus on the action or the result rather than the person who did it. This is where the Passive Voice is useful.

Structure: Subject + Verb 'to be' (past/present/future) + Past Participle (+ by Agent [optional])

Examples from the text:

Active: Julius Caesar introduced the concept of the leap year.
Passive: The concept of the leap year was introduced (by Julius Caesar).
Active: People call the year 46 BCE the "Year of Confusion."
Passive: The year 46 BCE was called the "Year of Confusion."
Active: Pope Gregory XIII commissioned a reform.
Passive: A reform was commissioned by Pope Gregory XIII.

Why use it? It makes the text sound more formal and objective. It emphasizes the event (the reform, the introduction) rather than the person.

Listening

Homework Proposal

Task: "The Lost Days Journal"

Imagine you are living in October 1582. You go to sleep on the night of October 4th. When you wake up the next morning, the government announces that it is now October 15th.

Write a diary entry (150-200 words) describing your confusion.

How do you feel about "losing" 10 days of your life?
What appointments or birthdays did you miss?
Do you believe the astronomers, or do you think it is a trick?
Requirement: Use at least two words from the vocabulary section and the phrasal verb "date back to" in your writing.