Why some months have 31 days, some months have 30 days, 28 days and 29 days

The Gregorian calendar we use today is from ancient Rome.

The Julian calendar established by the commander Julius Caesar during his reign evolved from it. This calendar stipulates that there are twelve months in a year, with a single month being a big month and thirty-one days, and a double being a small month and thirty days. There are 366 days in the year.

But there are only 365 days in a year, so what if there is one more day? It is said that the month of February was the Roman Empire.

In order to make this inauspicious month pass quickly, it was decided to reduce February by one day to twenty-nine days.

Julius Caesar was born in the seventh month, which happened to be the great moon, and he was very happy. His successor, Octavian.

Born in August, Octavian felt that it would be a loss of dignity for August to be a small month, so he subtracted one day from February and added it to August. Thus February becomes twenty-eight days, and August thirty-one.

After August became a big month, the following months were changed to small months for every single month, and big months for every double.

February is the second month of the Gregorian year, with 28 days in a common year and 29 days in a leap year.

The 365-day month arrangement in a normal year is completely in line with our thinking, that is, according to the big month, the small month, the big month, the small month, the big month, the small month, the big month, the small month, the big month, the small month, the small month, the big month, the small month, the small month, the right six big months and six small months.

The current solar calendar was established by Emperor Rosa the Great in 46 BC. Originally, he set a year of 12 months, 31 days in a single month and 30 days in a double month, so that there were 366 days in each year. However, Rome at that time had to execute a group of prisoners every February, so February was considered an unlucky month.

As a result, Caesar reduced February by one day, leaving 29 days.

Later, Caesar was killed, and Augustus became emperor, and he found that Caesar's birth was born in July with 31 days, and his birth was only 30 days in August, so he subtracted one day from February to August.

This leaves 28 days in February and 31 days in August. At the same time, he changed the number of days in the next few months, and it became what it is now. However, there is no other historical evidence for this, and it is likely to be just a myth, albeit a very old one.

1. The leap year of the Gregorian calendar is stipulated as follows: the earth's revolution around the sun is called a return year, and the return year is 365 days and 5:48:46 seconds. Therefore, the Gregorian calendar stipulates that there are common years and leap years, and there are 365 days in a common year, which is shorter than the return year, and there are four short days in four years, so one day is added every four years, and there are 366 days in this year, which is a leap year.

Four years with one day and more days than four return years will have more days after 400 years, so there are 3 fewer leap years in 400 years, that is, only 97 leap years in 400 years, so that the average length of the Gregorian calendar year is similar to that of the return year.

Therefore, it is stipulated that if the year is an integer hundred, it must be a multiple of 400 to be a leap year, for example, 1900 and 2100 are not leap years.

2. The earth we live on always revolves around the sun. It takes 365 days, 5 hours, 48 minutes and 46 seconds for the earth to complete one revolution around the sun, which is the day. For convenience, the year is set at 365 days, which is called a common year; Every four years, there is about an extra day, and when you add that day to February, there are 366 days in the year, which is called a leap year.

The origin of this can be traced back to Julius Julius Caesar in ancient Roman times. The current Gregorian calendar is directly related to the Julian calendar. The Julian calendar is a calendar named after the ancient Roman commander Julius Caesar, whose astronomers translated Julius as Julian, so the name is still used today.

The ancient Egyptians had always adopted the solar calendar, which used the solar cycle as the standard for the calendar year. They discovered early on that the length of the year was 365 and 1 4 days, so the Egyptians had 12 months of the year, 30 days per month, plus 5 days as an end-of-year holiday. The Greeks used the lunar calendar, i.e., the cycle of the moon, as the standard for calendar years.

After the Roman Emperor Caesar conquered Egypt, he brought back the Egyptian solar calendar. The original Rome also used a lunar calendar, which was very confusing, sometimes a few months away from the solar calendar, so that people could not distinguish between spring and autumn. Sosigis, a Greek astronomer in Alexandria, suggested that Caesar use the current Egyptian solar calendar instead, and that he should pay attention to intercalations every four years.

Caesar accepted the suggestion and decided to introduce the Gregorian calendar throughout Rome. The calendar stipulates that the first three years of each of the four years shall be a common year, with 365 days per year, and the fourth year shall be a leap year, with a year of 366 days. There are 12 months in a year, with 31 days for odd-numbered months and 30 days for even-numbered months, which are small months.

Then why must it be 31 days in an odd-numbered month, because Caesar's birthday is in July, and Caesar, in order to reflect his supreme majesty, requires that this month must be a big month, so astronomers set a single month as a big month. 6 big months and 6 small months, so that there is an extra day in the ordinary year, and only one day is deducted from a certain month. At that time, the death penalty in Rome was carried out in February, which was considered an inauspicious month, so subtracting one day from it, February became 29 days.

But we all know now that "one three, five, seven, eighty wax, 31 days is never bad". It's not 31 days in an odd-numbered month, so what's going on?

Back in ancient Rome, Julius Caesar died and was succeeded by his grandson Octavian. Octavian's birthday happened to be in August, and he also had to put on a show, so he ordered that August be set as the approximate, and that the next two months from August onwards be the big moon. In this way, there are 7 large months in the year, and one more day is subtracted from the "unlucky" month of February, making it 28 days.

Wu Guosheng, The Course of Science, Second Edition, Peking University Press, 100-101.

Because a year is about days, divided into 12 months, if there are 30 days in each month, then there are only 360 days in the whole year, a few days less, and if there are 31 days in a month, then there are 372 days in the year, and there are a few more days.

Therefore, the designers of the Western calendar artificially set some months to 30 days, others to 31 days, and later made some adjustments for other reasons, setting February to 28 or 29 days.

However, this method of setting has a big drawback, that is, the natural connection between the "month" and the "moon" of the calendar is severed, although the time of the month is about the same as the time of the moon's revolution, but the month and the moon phase do not coincide at all.

The Chinese are much smarter and have devised a calendar that takes into account both:

First of all, according to the law of the moon phase, the day of the new moon is the first day of the month, and of course the day before it is the last day of the previous month, so that the month or 30 days, or 29 days, and the moon phase exactly coincides;

Then, through the observation of the sun, the day when the sun shines directly on the Tropic of Capricorn, that is, the day with the longest night and the shortest day, is set as the winter solstice, and the month in which the winter solstice is located is set as the "winter moon";

The second month after the winter moon is defined as the "first month", which is the beginning of the new year;

In this way, the year is divided into 12 or 13 months, and if there are 13 months, a leap month can be set.

A month with 31 days is called a big month, and a month with 30 days is called a small month.

The big month of the Gregorian calendar has 31 days and the small month has 30 days. January, March, May, July, August, October and December are fixed as the big months every year; April, June, September, and November are small months. February is neither a big month nor a small month.

February has 28 days in a common year and 29 days in a leap year.

The big month of the lunar calendar has 30 days and the small month has 29 days. And the distribution of large and small months is irregular, and it varies from year to year.

Criteria for division. The lunar calendar is fixed with a small single month, a double moon large, and a leap month large. Except for the mantissa of the Common Era, the first month of the year in which the multiple of 5 is changed to the big month.

There are months in this program in 333 and 1 3 years, including (the first month is big, there are a total of 2000+ big months, small months, converted days, monthly average days (29 days, 12 hours, 44 minutes and seconds), and annual average days (365 days, 5 hours, 48 minutes and 20 seconds).

The 31 days are called the big moon, and the 30 days are called the small moon.

The 31-day months are: January, March, May, July, August, October, and December.

The 30-day months are: April, June, September, and November. .

February is a special month, with 28 days in a common year and 29 days in a leap year.

The big moon has 31 days and small months.

There are 30 days. <>

There are 12 months in a year, of which:

January, March, May, July, August, October, and December all have 31 days.

April, June, September, and November are all 30 days.

February is 28 days in a common year and 29 days in a leap year.

Memory nursery rhymes: 135780 (December), 31 days are never bad; Forty-six-nine winter (November) thirty full.

Dula Story: Do you know which month has 30 days and which month has 31 days? Learn from the baby boys.

There are 12 months in a year, each of which has a month, March, May, July, August, October, December, a total of seven months, 30 days in each month, April, June, September, November, a total of four months, 28 days in February in a normal year, and 29 days in February in a leap year.

The 31-day months are January, March, May, July, August, October and 12 months. The 30 days are April, June, September, November

January, March, May, July, August, October, December are 31 days.

April, June, and September are 30 days.

There are 28 days in February in a common year and 29 days in February in a leap year.

One, three, five, seven, eighty-twelve, these months have 31 days, and the rest of the months are 30 days, except for February.

The 31-day total is seven months, and the 30-day total is four months.

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