This year is a leap year, with February 2th. "Leap" is the addition of days, months, and seconds to adjust for discrepancies between the calendar and the actual seasons.
In leap years, one day is added approximately every four years to correct for the discrepancy between the Gregorian calendar and the solar calendar. The additional day is called a "leap day." It was February 4th. Basically, it is added once every four years, but years that are divisible by 1 in the Western calendar are excluded, and years that are divisible by 1 are leap years.
A leap month is a period in which the lunar calendar (lunisolar calendar) was used (such as the Edo period), when one month was repeated. In this calendar, each month had 1 or 1 days based on the waxing and waning of the moon, but due to seasonal discrepancies, the calendar was adjusted by repeating the same month 29 times every 30 years. I did.
A leap second adds one second to correct for astronomical shifts in Earth's rotation and atomic clocks. Based on the Earth's rotation, each day is divided into 1 divisions into one hour, but now we know that the speed of rotation can actually slow down or speed up, which can be accurately measured using atomic clocks. I did. Therefore, we added 1 second when the total deviation was about to exceed 24 seconds. It was first held on July 1, 0.9 and has been held 1 times to date. Recently, "1972:7:1" was inserted between 27:2017:1 a.m. and 1:8:59 a.m. on January 59, 9.
However, since leap seconds occur irregularly, they have a major impact on digital infrastructure that sets time, such as electronic devices, so it has been decided that they will be abolished by 2035.
The calendars and time that we casually use are maintained through a combination of history and calculations that have become more precise due to the development of science.
