Months having 30 and 31 days is a result of various ancient traditions that have been in place for thousands of years. In the early days, calendars were not standardized, meaning that different cultures followed different months and the lengths of those months.
For example, the ancient Egyptian calendar was composed of 12 months of 30 days, plus five days that were considered to be outside of month; Babylonian and Elamite months typically posted 29 or 30 days.
The early Roman calendar also had 12 months of varying length, and the length was determined by the positions of the stars and moons. Under this system, all of the months had either 29 or 31 days, with February being the only exception, as it had 28 days.
After 46 BC, Julius Caesar changed the Roman calendar to follow the Egyptian model of 12 months of 30 days each and an extra month at the end of the year.
The 30- and 31-day months we have today follows a calendar system first created by Julius Caesar in 45 BC. This model, referred to as the Julian Calendar, was adopted throughout the Roman Empire and eventually formed the basis of our modern Gregorian calendar, which is used worldwide.
So, the 30- and 31-day months remain a vestige of this longstanding tradition.
Table of Contents
Why do we have 12 months instead of 13?
The 12-month calendar originated in Mesopotamia and was based on the movements of the moon. Because of the way it was determined, the lunar months were shorter than the solar year, so additional days were added or months were shifted to compensate.
At one point there were 13 lunar months in the year, but over time, it was decided to have 12 months and an additional ‘leap month’ added every few years.
The 12-month calendar is still used today, although with the addition of a leap year every fourth year which adds an extra day in the month of February. This ensures that the calendar aligns with the solar year and remains in sync.
Who invented 30 days in a month?
We don’t know exactly who invented the 30-day month, but it is believed to have been created by the early Egyptians and Mesopotamians. Prior to the Egyptians and Mesopotamians, the Sumerians and Babylonians used a calendar that had only 28 or 29 days in a cycle.
These cultures came up with the concept of a lunar year, which is a full cycle of lunar phases as observed from Earth.
In Ancient Egypt, a 12-month lunar year of 360 days was developed. This was important for seasonal festivals and agricultural timeline events. The Egyptians soon realized that if the year was divided into 12 lunar months of 30 days each the total would be 360 days.
This calendar then spread to other cultures such as the Greeks, though it was adjusted slightly because their calculations showed the solar cycle was slightly longer than 360 days, so a 5th month was added every few years to keep the calendar in sync with the solar cycle.
The concept of the 30-day month then spread to the Romans who also adjusted it slightly as they observed that a lunar cycle was actually slightly shorter than 30 days. This then became the Julian calendar, and it is still used by many cultures today.
Overall, the exact identity of who invented the 30-day month remains unknown, but it is believed to have been developed by the early Egyptians, and later adjusted by the Babylonians and Romans.
What was the 13th month called?
The 13th month was called Undecember, but it is no longer used. It was added in 45 BC by Julius Caesar as part of his reform of the Roman calendar. Before these changes, the Roman calendar was a lunar calendar with 10 months.
Caesar decided to create an extra month, bringing the calendar up to 12 months and making the seasons more consistent rather than drift around like before. The extra month, therefore, was added to the end before the transition to the next year.
The name Undecember means “10th month”— which is how it was known before Caesar’s reforms.
It remained as a 13th month for several years and was celebrated by the populous with festivals, offerings and music. Interestingly, it was believed that babies born in this month had a great life ahead of them.
However, by the 4th century AD, it had vanished from the calendar and by the 8th century even the memory of the 13th month had been lost.
When did we stop using 13 months?
The use of 13 months in a calendar year dates back to the Roman Calendar, which was based on lunar cycles. The Roman Calendar was eventually replaced by Julian Calendar in 45 BC, which used 12 months and included a leap day every four years.
This later became the Gregorian Calendar, which is the calendar used worldwide today. This calendar was established in 1582 and was proposed by the owner of the Gregorian calendar, Pope Gregory XIII, as a way to amend errors in the Julian Calendar.
This calendar also utilized 12 months and a leap day every four years. Thus, the use of 13 months ceased when the Gregorian Calendar was established in 1582.
Was there supposed to be 13 months in a year?
No, there was not originally supposed to be 13 months in a year. The calendar we use today, called the Gregorian calendar, most commonly consists of twelve months, which were determined by the moon’s cycles.
This was determined by the ancient Romans, who initially divided the year into 10 months and eventually added two more. This calendar is based on a cycle of four years known as a leap year, where an extra day (February 29th) is added, to account for the slight variance in the length of our year.
The reason for this is because it takes approximately 365. 24 days for the Earth to make one complete revolution around the sun. This means that it does not perfectly align with the 12-month, 29. 5-day lunar cycle.
While the concept of 13 months have been suggested in a few different cultures, the Gregorian calendar is still the most commonly used today and does not contain any additional months.
What determines if a month has 30 or 31 days?
The number of days each month has is determined by the Gregorian calendar, which was first introduced in 1582. In the Gregorian calendar, most months have either 30 or 31 days, with the exceptions of February which has 28 days and 29 days if it’s a leap year.
The length of each month in the Gregorian calendar is set by a long calculation that looks at the position of the Earth in relation to the Sun and determines the appropriate length of a month and number of days per month.
Depending on the month, there are rules that determine whether the month has 30 or 31 days. For example, April, June, September, and November have 30 days, while the remaining months have 31 days.
Who decided that a month is 30 days?
No one knows exactly who decided that a month is 30 days, but we do know that the concept of months has been around since ancient times. In ancient Babylon, during the reign of Nabonassar (747–734 BC), each year was divided into 12 months – each month lasted either 29 or 30 days, primarily based on the lunar cycle.
According to the Enuma Anu Enlil, a set of Babylonian astronomical diaries, the average Babylonian month contained 30 days, and this number was used as a standard for many other cultures.
In Ancient Rome, the lengths of the months were adjusted to fill out the 365-day year. Julius Caesar was one of the first leaders to reform the Roman calendar, and he introduced a 365-day year that contained 12 months of 30 or 31 days each.
After Julius Caesar’s death, the Roman emperor Augustus made a few further adjustments to the calendar, by shortening August and lengthening February, which is why February is still the shortest month in the modern Roman calendar.
The Romans incorporated many of their month lengths and names into the modern calendar, and most of us still use the same system today. Although the length of each month may differ slightly depending on the calendar system you’re using, the 30-day month is present in most calendars around the world.
Why is 29 days every 4 years?
Every 4 years, the calendar year is made up of 365 days, with the exception of leap year – which is a 366 day year. The extra day in this year is added on February 29th to account for the slight discrepancies that happen as the planet orbits around the sun.
Leap years occur every four years as a way of accounting for the 365 ¼ days it takes for the Earth to orbit the sun. Since a regular year is 365 days and does not account for the ¼ day discrepancy, the leap day is added to the calendar every four years to make up for the discrepancy.
This is why February 29 only comes around every 4 years – because it is an extra day to account for the days we miss from not having a leap day every single year.
The practice goes back to the ancient Roman calendar, which was made up of 355 days. The Romans added an extra month of 22-23 days every other year in order to sync their calendar with the solar year.
Later, Roman Emperor Julius Caesar reworked the calendar in 46 BC, creating the Julian calendar. He worked out the cycle of leap years with only one rule – every year that is divisible by four would be a leap year.
So the answer is that February 29 comes around every four years because it is an extra day added to the calendar year to account for the discrepancy between the 365 day calendar year and the 365 ¼ day solar year.
Who added an extra day to January giving it 31 days instead of 30?
Julius Caesar is generally credited with adding an extra day to January in 46 B. C. The extra day was added to make the new Julian calendar, which was based on a solar year and had twelve months of alternating 30 and 31 days.
This calendar system was more accurate than the Roman calendar of the time, which was developed in the eighth century B. C. and relied on the lunar cycle. Caesar ordered the extra day be placed at the end of the month in an effort to keep the calendar aligned with the phases of the moon.
With the extra day, January began to regularly have 31 days, with only February having an alternation. This system was used as the basis for calendar design in the centuries to follow and remains in use today.
Why do we skip February 29?
February 29 is skipped because it is the leap day, added every four years to make up for the fact that our calendar year is slightly shorter than the time it takes the Earth to orbit around the Sun. The addition of the leap day helps keep our calendar year in sync with the solar year, or the calendar year we use to measure the seasons.
Most years, February has 28 days. However, every fourth year, an extra day is added in the month of February, creating February 29. This is known as leap day, or leap year day. The purpose of the leap day is to help keep our calendar year in step with the solar year.
This is because the solar year is actually 365. 24 days long, while the calendar year length is often set at 365 or 366 days. Thus, a leap day is added to the calendar every four years to make up for the difference.
How was the number of days in a month determined?
The number of days in a month was determined by the lunar cycle. For centuries, many cultures tracked the lunar cycle to measure time. They noticed that the lunar cycle was about 29. 5 days long, and used this measure to divide the cycle into 12 distinct months.
Each month was divided into either four or five weeks, and each week was composed of 7 days. This interpretation is the basis of the number of days in a month, with some months such as February occasionally having one more or one less day due to the different phases of the moon throughout the year.
Why is October not the 8th month?
October is not the 8th month because the way that the Gregorian calendar is set up, it begins in January and ends in December. The months of January, February, March, April, May, June, July, August, September, October, November, and December are in that order.
So, October is actually the 10th month of the year, regardless of the fact that it appears to be the 8th when you look at a calendar page. The concept of what we now recognize as the Gregorian calendar was originally set up in the 16th century by Pope Gregory XIII, and since then, the months of the year have appeared in the same order.
Why are some months 30 and some 31?
The months in the Gregorian calendar normally have either 30 or 31 days. This is due to the way in which the lunar cycle and solar cycle overlap to create our calendar year. The lunar cycle is about 29.
5 days long, meaning nearly every month has to either add or subtract a day to line up with the solar cycle. The length of the months alternates accordingly – a 30 day month will be followed by a 31 day month, and so on.
February is the only month that doesn’t follow this pattern, since it is the only month that is affected by leap years. In the Gregorian calendar, a leap year occurs every four years in order to account for the solar cycle being slightly more than 365 days.
Since the extra day needed to make up the difference is added to the month of February, it becomes the only month with a variable length – 29 days instead of the usual 30.
