September means seventh. It is the ninth month. The names are a fossil. And the calendar behind them has been corrected, resisted, and corrected again for over two thousand years.
The names September, October, November, and December come from the Latin words for seven, eight, nine, and ten. They made sense when the Roman year started in March. January and February became part of the calendar later, pushing everything forward, and the names stayed wrong. Twelve months exist because there are a little more than twelve lunar cycles in a solar year, making twelve a natural starting point. But twelve lunar months fall short of a full solar year, and that mismatch has driven calendar adjustments for thousands of years.
Daniel opens the episode by noticing the number mismatch in those four month names. What follows moves through the lunar and solar calendar problem, Julius Caesar’s reform in 46 BC and the year of confusion that preceded it, the eleven minutes per year that accumulated into a ten-day error, Pope Gregory XIII’s 1582 correction, Britain’s resistance until 1752, and the disputed story of the eleven-day protests. The episode closes on a line about September that earns its laugh from everything that came before.
Daniel is nine. He asks the questions, refuses to accept easy answers, and picks every episode topic himself.
MomCo-host & Researcher
Mom does the digging - finding the sources, checking the claims, and translating them into something a nine-year-old will actually sit still for.
Things to remember
01
September through December carry names meaning seven through ten because the Roman year once started in March.
02
Twelve months exist because there are a little more than twelve lunar cycles in a solar year.
03
Julius Caesar reformed the Roman calendar in 46 BC, introducing 365 days and a leap day every four years.
04
he Gregorian calendar corrected the Julian calendar's drift in 1582 by dropping ten dates and refining the leap year rule.
“Twelve months is basically the Moon and the Sun refusing to divide evenly.”
Daniel
Full transcript10 min · 1,004 words
DanielMom, I was just looking at my calendar on my wall and started wondering. Why are there 12 months in a year? Why not 10 or 13? And why do September, October, November, and December sound like they mean 7, 8, 9, and 10, but they are the 9th, 10th, 11th, and 12th months?
MomDaniel, you just noticed one of the best clues in the entire calendar. Those names are a fossil.
DanielWhat? A fossil?
MomYes, a leftover from when the Roman year started in March. September was the 7th month, October the 8th. The names stopped matching when the calendar changed.
DanielSo, the calendar used to start in March?
MomIn the oldest Roman tradition, yes. The year began in March, which is why September through December still carry names connected to 7, 8, 9, and 10. January and February became part of the Roman calendar later. Over time, Rome ended up with a calendar built around 12 lunar months, with extra days, or even an extra month, inserted when needed to keep it aligned with the seasons.
DanielBecause 12 lunar months are shorter than a solar year.
MomExactly. 12 lunar cycles are only about 354 days, while the solar year is about 365 and a quarter. The Romans were supposed to correct that by occasionally inserting an extra month, but the system was complicated and inconsistently managed. And by Julius Caesar's time, the calendar had drifted badly out of alignment with the seasonal cycle.
DanielSo, what did Caesar do?
MomCaesar replaced the old system with a solar calendar, apparently with help from an Alexandrian astronomer named Sosigenes. The new calendar averaged 365 and a quarter days, normally 365, with an extra day every fourth year.
DanielThat extra day is the leap year.
MomAnd getting the seasons back into place required an extraordinary one-time correction. The year 46 BC was stretched by adding extra months, making it extraordinarily long. It is sometimes called the year of confusion.
DanielThey fixed a confusing calendar by creating an even more confusing year.
MomThe Julian calendar was a genuine improvement, but it was still slightly off, about 11 minutes too long each year. 11 minutes sounds tiny.
DanielBut 11 minutes times hundreds of years adds up.
MomBy the 1500s, the error had grown to 10 days. Pope Gregory XIII ordered a correction in 1582. In countries adopting the reform, October 4th was followed immediately by October 15th.
DanielHmm, 10 days just disappeared from the calendar.
MomAnd he adjusted the leap year rule so the calendar would drift much more slowly. Century years, like 1700 or 1800, would only be leap years if divisible by 400. That is why the year 2000 was a leap year, but 1900 was not.
DanielSo we had to change the rule for leap years to fix the problem caused by Caesar's leap year rule. A calendar correction correcting the calendar correction.
MomCatholic countries began adopting the new calendar in 1582, but Protestant countries were much slower. Religious and political distrust of a reform introduced by a pope played a role, so different parts of Europe ended up using different calendars for generations.
DanielHow long did Britain resist?
MomUntil 1752. By then, the difference had grown to 11 days. When Britain finally switched, September 2nd was followed directly by September 14th.
Daniel11 days just gone. Hmm, did people notice?
MomThis is where history and legend get mixed together. There is a famous story that angry crowds demanded, Give us our 11 days! The phrase even appears in a painting by William Hogarth. But historians debate whether the enormous calendar riots described in later stories really happened the way people imagined them.
DanielSo, even the story about people being confused by the calendar is confusing.
MomAppropriately enough. What is certain is that changing the calendar affected real dates people used for business, legal agreements, and everyday life. Changing 11 dates on paper did not mean everyone's routines instantly changed with them.
DanielSo the disruption was real, even if the riots might be exaggerated.
MomExactly. And now, back to your original question. Why 12?
DanielRight, why 12 specifically?
MomBecause the moon gives you a natural way to divide the year. There are a little more than 12 lunar cycles in one solar year, so calendars built around lunar cycles naturally tend toward about 12 months. But 12 lunar months do not make a full solar year. And that mismatch between the moon and the sun is one reason calendars have needed adjustments for thousands of years.
DanielSo 12 months is basically the moon and the sun refusing to divide evenly.
MomThat is an excellent description of a large part of calendar history.
DanielSo when I look at a calendar, I am looking at layers of history. Ancient Roman traditions, Caesar's reform, Gregory's correction, and countries that took centuries to agree on which version to use.
MomAnd the names of the last four months have been wrong for over 2,000 years. And everyone just decided to keep them.
DanielNow, that's a very interesting explanation, and I kind of like that.
MomSo, Daniel, what is one thing you are taking with you today?
DanielSo, let's see. September, October, November, and December are named for 7, 8, 9, and 10 in Latin because the Roman year once started in March. 12 months make sense because there are a little more than 12 lunar cycles in a solar year. But the moon and the sun do not divide evenly, which has caused calendar problems for thousands of years.
DanielJulius Caesar reformed the Roman calendar in 46 BC, apparently with help from the astronomer Sosigenes, creating a 365-day calendar with a leap day every four years. But the Julian calendar was still about 11 minutes too long each year, and by the 1500s that had added up to 10 days.
DanielI also remember that Pope Gregory XIII corrected it in 1582, dropping 10 dates from October in countries adopting the reform and refining the leap year rule. And Britain did not switch until 1752.
MomThe calendar has been wrong, corrected, resisted, and corrected again. And the names from the old version are still there every time you look at the last four months. September is the 9th month that thinks it is the 7th, and has been for over 2,000 years without ever changing its name.
