O leap year happens every four years and has duration of366 days, unlike the others that have 365 days. The inclusion of a day was made to bring the calendar closer to the translation movement of Earth, the time it takes the planet to go around the Sun, which is 365 days, 5 hours, 48 minutes and 46 seconds. Those hours that exceed 365 days are compensated every four years, on February 29th.
the leap year It was adopted in the dictatorship of Julius Caesar, about 50 years a. Ç., at Ancient Rome, to adjust the calendar year to the solar year. However, the choice of February 29 to be added every four years only took effect in 1582, with the Gregorian calendar.
See too: Earth movements: what are they, characteristics, effects
How did the leap year come about?
A legend said that the first calendar Roman it had been created by Romulus, the founder of Rome, with 304 days divided into 10 months. Later, Romulus' successor, Numa Pompilius, created a new calendar in which the year consisted of 355 days, adding two months to the count.
O Roman calendar became luni-solar and had the adoption of an extra month, called mensisinterim, every two years so that there was alignment with the solar year. In the model instituted by Numa Pompílio, the year started in March and ended in February.
Each month was divided into three periods:
- Calendars: first days of the month
- Ninths: middle of the month
- Gone: last days of the month
Julian calendar
Centuries later, with the difference between the calendar at the time and the solar year, the Roman dictator Julio Cesar asked the astronomer Sosigenes to find a way to reduce that disparity. Sosigenes based on what was adopted by the Egyptians and defined 365 regular days and an additional every four years, thus creating the Julian calendar.
The Julian calendar divided the 365 days into 12 months and, as it is not an exact division, some months were left with 30 days and others with 31. Some rules defined by Astronomywere adopted, as each month encompasses the four phases of the Moon.
With the end of the adoption of the interim years, the first and last month of the Julian calendar became January and December, respectively. In addition, the seasons started to have defined start dates: eighth day before the beginning of the months of April, July, October and December.
Origin of the term "leap"
As the counting of days was done in a regressive way: there are three days left until the calendas, for example, the additional day of the leap year was included in February, as determined by Julius Caesar: 'ante diem bis sextum Kalendas Martias', a term in Latin that meant the repeat of the sixth day before the March calendars (March 1st), “repeating” February 24th, hence the origin of the word leap (twice six).
Why does February have fewer days?
After the death of Julius Caesar, the Roman senate decided to honor the emperor by changing the name of the month Quintiles, who had 31 days, to Julius (July). Subsequently, in order to honor Emperor Caesar Augustus, the month of sextile started to be called augusts (August), but this month had only 30 days and for both honors to be equalized, it was decided to add a day in August.
For this to be possible, the solution was remove a day from the month of february, which already had one less date, due to the repetition in leap years. Thus, February was left with 28 days in common years and 29 (with the repetition of the 24th) in leap years.
Year of Confusion
The Julian calendar was adopted, but there was still an 80-day difference from the solar year. To solve the problem of counting, Julius Caesar determined that the year 46 a. Ç. had 455 days, which earned the period the name of the Year of Confusion.
Read too: Curiosities about the Solar System
Gregorian calendar
In 1582, the Pope Gregory XIII made changes so that the difference between the length of the year and the calendar were minimized, this calendar became known as Gregorian and is what we use until today.
Rearranging the dates changed the additional leap year day from February 24th to February 29th. In addition, advised by the astronomer Christopher Clavius, the pope determined that the day after October 4, 1582, was October 15, a suppression of days that became known as “days that never happened" or “lost days", decreasing the 11-day difference that had been generated from the Julian period so that the calendar could be adjusted.
How are leap years calculated?
The first calculation of leap years was defined in the Julian period. The responsible astronomer defined that a day be added to the month of February every four years. After the death of Julius Caesar, not all leap years were every four years, some occurred every three, which generated an excess of days. To circumvent the excess of days created by incorrect counting, Emperor Augustus Caesar determined that between 12 BC. Ç. and 8 a. Ç. there were no leap years present in the Julian calendar.
With the change to the Gregorian calendar, the calculation was adopted that leap years would be the divisible by four and, to avoid further difference with the solar year, the account included that years ending in 00 (multiples of 100) would only be leap if the result of dividing by 400 was exact.
The calculation is as follows:
→ The year is divisible by 4 when you can divide your ten by 4:
2020 = 20 ÷ 4 = 5, i.e, 2020 is a leap year
Thus, the next leap years divisible by 4 will be 2024, 2028, 2032, 2036, 2040, 2044, 2048, 2052.
→ What about the years ending in 00?
400 ÷ 400 = 0 => 400was a leap year
500 ÷ 400 = 1,25 => 500it was not a leap year
By this rule, the next year ending in 00 that will be leap year is 2.400.
By Lorraine Vilela
Brazil School Team
Source: Brazil School - https://brasilescola.uol.com.br/curiosidades/ano-bissexto.htm
