The reason for February is only 28 or 29 days

Each calendar month has between 30 and 31 days, but February is only 28 or 29 days if it is a leap year, due to the retention of the previous Roman calendar.

The original Roman calendar was issued by Romulus, the first emperor of Rome. His calendar is based on the moon's cycle, which is similar to the Lunar calendar of the Eastern people, but only 10 months. The 10 months of this calendar start in March and end in the end of December (note that the January, February, March, . numbering is due to the Vietnamese translation, and in the original version of the calendar. Romans as well as how to translate many languages ​​in the world each month have their own names.

So one year has only 10 months, ie there is a period of two cycles of the Moon that is not included in the calendar, because Romulus thinks this is a winter time that doesn't mean anything to agriculture, so does it? There should be a convention.

February has 28 or 29 days due to the retention of the previous Roman calendar.

Around the 8th century BC, Numa emperor Pompilius was the one who decided to take another two months into the calendar for 12 full Moon cycles. Each month has 28 days, making the calendar last 12 full Moon cycles, a total of 354 days. However, Pompilius said that the 28 was an unfortunate number, so he decided to give one more day to 29 days in January, and February for some reason remained the same for only 28 days.

The lunar calendar loses its weakness, it does not reflect the period of seasonal weather changes, because this cycle is associated with the earth's movement around the sun. Therefore, the Romans decided to add a leap month every 27 days after February 23 (those years in February only 23 days).

Making changes like this makes scheduling troublesome. By about 45 BC, Julius Caesar decided to change this calendar system. He stayed the same for 12 months but added days in the months so that those 12 months coincided with the sun's cycle (the position cycle of the sun in the sky, not the earth cycle moving around the sun because of that time I don't know the earth has orbit around the sun).

Caesar also set a rule every February every year to add one day to match the sun's cycle of 365.25 days, which is essentially close to the real cycle. of the earth around the sun, we know now 365.2425 days.

There is a source of documents that originally stated in Caesar's calendar, February has 29 days and every 4 years it is added one day to 30 days, ie there is no big difference with other months. However, later in the month of renaming, the second day of the ninth of February was transferred to August because this month was named after Augustus (Emperor founded the Roman empire), so that the month was of similar length. July's July - the name of Julius Caesar.

The calendar that people use today is the Roman calendar that is further refined. The division of months remains the same to respect history and that's why there are fewer days in February than the other months. Basically this is just a convention, does not affect the use of human time.