How Was The Calendar Invented?

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2 Jan 201503:29

Summary

TLDRThis DNews episode explores the history and significance of the Gregorian calendar, introduced by Pope Gregory XIII in 1582 to correct the drift of Easter from the spring equinox. It explains the calendar's leap year system and its accuracy relative to the solar cycle. The video also touches on the Julian calendar, the origin of our current year numbering, and alternative calendar systems, concluding with a humorous suggestion to switch to the Julian calendar for a second chance at New Year's resolutions.

Takeaways

📅 The Gregorian calendar is the most widely used civil calendar today, named after Pope Gregory XIII who introduced it in 1582.
🌕 The calendar system was reformed to ensure that Easter, traditionally celebrated on the first Sunday after the first full moon following the spring equinox, would not drift out of alignment with the lunar cycle.
⏭️ When the Gregorian calendar was adopted, the Catholic world had to jump forward by 10 days to correct the accumulated discrepancy.
🌐 The adoption of the Gregorian calendar was not universal; some countries, like Russia, only switched in the 20th century.
🔢 The Gregorian calendar refines the leap year system, with a leap year occurring every 4 years except for years divisible by 100, unless they are also divisible by 400.
🌞 Our solar year is not exactly 365 days; it's approximately 365.2425 days, which is why the leap year adjustments are necessary to keep the calendar aligned with the seasons.
📚 Before Julius Caesar, the Roman calendar was inconsistent and subject to political manipulation by the high priest.
🎉 The Julian calendar, introduced by Julius Caesar in 45 BCE, established a more standardized system with a leap year every four years.
🗓 The discrepancy in the Julian calendar's alignment with the solar year became noticeable over centuries, leading to the need for further reform.
📜 The current year numbering system, with AD and BC, was established by Christian monk Dionysius Exiguus in 525, who calculated the year of Jesus's birth as 753 in the Roman calendar.
🌐 In academic and scientific contexts, BCE (Before Common Era) and CE (Common Era) are used to avoid religious connotations and to be more inclusive.
🌟 The Gregorian calendar is preferred for predicting astronomical events due to its regularity, despite a minor inaccuracy that will become significant only in the year 4909.

Q & A

What is the Julian Calendar?
-The Julian Calendar is the calendar introduced by Julius Caesar in 45 BCE, which had 365 days every year with an extra day added every four years to account for the slight discrepancy between the solar year and the calendar year.
Why was the Gregorian Calendar introduced?
-The Gregorian Calendar was introduced by Pope Gregory XIII in 1582 to correct the drift of the date of Easter and to better align the calendar with the solar year, as the Julian Calendar was slightly too long over time.
What was the significance of the spring equinox in determining the date of Easter?
-Easter is traditionally celebrated on the Sunday after the first full moon following the spring equinox, which is around March 21st. The Gregorian Calendar was adjusted to ensure that this date did not drift too far from the solar event.
How did the implementation of the Gregorian Calendar affect the date?
-When the Gregorian Calendar was implemented, the Catholic world jumped forward by 10 days to realign with the solar year.
Which country was one of the last to adopt the Gregorian Calendar?
-Russia was one of the last countries to adopt the Gregorian Calendar, doing so after the October Revolution in 1917.
What is the difference in the leap year calculation between the Julian and Gregorian Calendars?
-While both calendars have a leap year every four years, the Gregorian Calendar excludes years divisible by 100 unless they are also divisible by 400, making it more accurate.
How does the Earth's revolution around the Sun affect the need for a leap year?
-The Earth's revolution around the Sun is not exactly 365 days but approximately 365 days, 5 hours, 48 minutes, and 46 seconds, which necessitates the addition of a leap day to keep the calendar year aligned with the solar year.
Why did the Roman Senate name July after Julius Caesar?
-The Roman Senate named July after Julius Caesar to honor him for his reform of the calendar with the introduction of the Julian Calendar.
What does AD stand for and why was it introduced?
-AD stands for Anno Domini, which means 'The Year of Our Lord' in Latin. It was introduced by Christian Monk Dionysius Exiguus in 525 to count years from the birth of Jesus, which he calculated to be in the Roman year 753.
Why do academic and scientific communities often use BCE and CE instead of BC and AD?
-BCE (Before Common Era) and CE (Common Era) are used to maintain neutrality and to be more inclusive of people of all faiths, avoiding the religious connotations of BC (Before Christ) and AD (Anno Domini).
What is the expected accuracy of the Gregorian Calendar until when?
-The Gregorian Calendar is expected to remain accurate until the year 4909, after which it will be a day ahead of the solar year.

Outlines

00:00

📅 The Origin and Evolution of the Gregorian Calendar

This paragraph delves into the history and reasons behind the Gregorian calendar's establishment by Pope Gregory XIII in 1582. It discusses the calendar's purpose, particularly the need to align Easter with the spring equinox, and the adjustments made by Aloysius Lilius to correct the discrepancy. The summary also touches on the calendar's adoption by different countries over time, including Russia's late adoption after the October Revolution. The paragraph explains the leap year system of the Gregorian calendar, which is more accurate in reflecting the Earth's revolution around the Sun, and contrasts it with the Julian calendar's simpler leap year rule.

Mindmap

Keywords

💡Gregorian Calendar

The Gregorian Calendar is the most widely used civil calendar in the world today, introduced by Pope Gregory XIII in 1582 to correct the inaccuracies in the Julian Calendar. It is central to the video's theme as it discusses the calendar's history and its impact on the determination of religious holidays like Easter. The script mentions that the calendar was adjusted to ensure Easter would fall on the Sunday after the first full moon after the spring equinox, which had been drifting away from its traditional date.

💡Julian Calendar

The Julian Calendar was introduced by Julius Caesar in 45 BCE and was the predominant calendar in the Roman world for over 1600 years. It is significant in the video as it is the predecessor to the Gregorian Calendar and is still used by some communities today. The script refers to the Julian Calendar's inaccuracies, which led to the need for the Gregorian reform, and its method of adding an extra day every four years to account for the discrepancy in the solar year.

💡Leap Year

A leap year is a year with an additional day added to the calendar to keep it synchronized with the astronomical year. In the video, leap years are discussed in the context of both the Julian and Gregorian Calendars. The Gregorian Calendar refined the leap year system by adding exceptions for years divisible by 100, unless they are also divisible by 400, as a way to more closely match the solar year's actual length.

💡Solar Cycle

The solar cycle refers to the time it takes for the Earth to complete one orbit around the Sun, which is approximately 365 days, 5 hours, 48 minutes, and 46 seconds. The video explains that the Gregorian Calendar's adjustments to leap years were made to align more accurately with the solar cycle, which is essential for predicting astronomical events like equinoxes and solstices.

💡Spring Equinox

The spring equinox is an astronomical event that marks the beginning of spring in the Northern Hemisphere, occurring around March 20th or 21st when day and night are approximately equal in length. The video mentions the spring equinox in relation to determining the date of Easter, which is supposed to fall after the first full moon following this event.

💡Aloysius Lilius

Aloysius Lilius was an Italian doctor and astronomer who played a key role in the reform of the calendar, as commissioned by Pope Gregory XIII. His work is highlighted in the video as the basis for the Gregorian Calendar's leap year adjustments and the overall correction of the calendar's drift from the solar cycle.

💡Daylight Saving Time

Daylight Saving Time is a practice of setting the clock ahead by one hour during certain months to extend evening daylight in the local time zone. The video humorously compares the public's reaction to the introduction of the Gregorian Calendar, which involved jumping forward 10 days, to the annoyance some people feel with the biannual changes of Daylight Saving Time.

💡October Revolution

The October Revolution refers to the overthrow of the Provisional Government in Russia, which occurred in October 1917 according to the Julian Calendar, but was in November by the Gregorian Calendar's standards. The video uses this historical event to illustrate the late adoption of the Gregorian Calendar by Russia and the confusion it caused in dating.

💡Anno Domini

Anno Domini, abbreviated as AD, is a term used to label years in the Gregorian calendar, meaning 'In the year of the Lord' in Latin. It was introduced by the Christian monk Dionysius Exiguus to count years from the birth of Jesus. The video explains that AD does not stand for 'After Death,' as commonly misunderstood, but rather 'Anno Domini', emphasizing the religious significance of the calendar system.

💡Common Era

Common Era, abbreviated as CE, is a secular term used in academic and scientific communities to denote years in the Gregorian calendar without religious connotations. It is equivalent to AD and is used alongside BCE (Before Common Era), which corresponds to BC (Before Christ). The video mentions these terms to highlight the effort to make historical dating systems more inclusive.

💡Lunar Calendar

A lunar calendar is a calendar based on the cycles of the moon's phases, typically used by cultures in regions with less pronounced seasonal changes. The video contrasts the Gregorian solar calendar with lunar calendars, noting that while the latter are less common globally, they are still significant for certain communities and their traditions.

Highlights

The Gregorian calendar was implemented by Pope Gregory the thirteenth in 1582 to correct the date of Easter.

Easter's traditional date was the first Sunday after the first full moon following the spring equinox, which was drifting out of sync with the solar event.

Italian scientist Aloysius Lilius was commissioned to fix the calendar discrepancy to ensure the correct celebration of Christ's rebirthday.

The switch to the Gregorian calendar caused the Catholic world to jump forward by 10 days.

Non-Catholic countries took hundreds of years to adopt the Gregorian calendar, with Russia switching after the October Revolution in 1917.

The Gregorian Calendar's accuracy comes from its revised approach to leap years, including exceptions for years divisible by 100 but not 400.

The Earth's revolution around the sun is not a perfect 365 days but includes an additional 5 hours, 48 minutes, and 46 seconds.

Before Julius Caesar, the Roman calendar was manipulated for political reasons, affecting the length of years.

Julius Caesar standardized the calendar with 365 days per year and an extra day every four years, known as the Julian calendar.

The Julian calendar's average year was 11 minutes and 14 seconds too long, an error that became evident over centuries.

Caesar's birth month was renamed July in his honor after he reformed the calendar.

The year count starts from 753 in the Roman calendar, as determined by Christian Monk Dionysius Exiguus, leading to the use of BC and AD.

In academia, BCE (Before Common Era) and CE (Common Era) are used instead of BC and AD for neutrality.

The Gregorian Calendar is preferred for predicting seasonal changes due to its regularity, despite a minor inaccuracy that will become significant in 4909.

The Julian calendar is still used by some, offering a humorous suggestion to switch and retry new year's resolutions.

Different cultural calendars rely on lunar cycles rather than solar, impacting the dates of seasons and events.

The video invites viewers to share their experiences with different calendars and whether they use the Gregorian calendar.