What is the importance of leap year in the calendar?

What is the importance of leap year in the calendar?

February 29 is a rare case, as it is the only day that does not occur annually, but rather is experienced by humans once every four years. Those born on this day are considered among the unluckiest among humans because their birthday does not occur annually, but rather once every four years.

Leap years are years that contain 366 calendar days instead of 365 calendar days, and they occur every four years in the Gregorian calendar, which is the calendar currently used by the majority of countries in the world. The extra day, known as leap day, is February 29, which does not exist in non-leap years.

In other words, every year that is divisible by four is a leap year, such as 2020 and 2024, with the exception of some centennial years or years that end with the number 00, such as the year 1900.

The “Live Science” website, which specializes in science news, published a detailed report, which Al Arabiya Net viewed, explaining the reasons and how the “leap year” appeared, and its history in the world.

The report notes that other non-Western calendars, including the Islamic calendar, the Hebrew calendar, the Chinese calendar, and the Ethiopian calendar, also have versions of leap years, but these years do not all come every four years and often occur in years different from those in the Gregorian calendar. Some calendars also contain multiple leap days or even abbreviated leap months.

In addition to leap years and leap days, the (Western) Gregorian calendar also contains a small number of leap seconds, which have been added sporadically to certain years, most recently in 2012, 2015 and 2016. However, the International Bureau of Weights and Measures (IBWM), the organization responsible for global timekeeping, will eliminate leap seconds from 2035 onwards.

Why do we need leap years?

The Live Science report says that leap years are very important, and without them, our years would look completely different in the end. Leap years exist because one year in the Gregorian calendar is slightly shorter than a solar or tropical year, which is the amount of time it takes the Earth to completely revolve around the sun at once. The calendar year is exactly 365 days long, but the solar year is approximately 365.24 days, or 365 days, 5 hours, 48 ​​minutes, and 56 seconds.

If we do not take this difference into account, every year that passes we will record a gap between the beginning of the calendar year and the solar year that will expand by 5 hours, 48 ​​minutes and 56 seconds every year, and this will change the timing of the seasons. For example, if we stopped using leap years, after about 700 years, summer in the Northern Hemisphere would start in December instead of June.

Adding leap days every fourth year largely eliminates this problem because the extra day is roughly the same length as the difference that accumulates during this time.

However, the system is not perfect: we gain about 44 extra minutes every four years, or one day every 129 years. To solve this problem, we skip leap years every centennial year except for those that are divisible by 400, such as 1600 and 2000. But even then, there was still little difference between calendar years and solar years, which is why the International Bureau of Weights and Measures also experimented with leap seconds.
But in general, leap years mean that the Gregorian (Western) calendar remains in sync with our journey around the sun.

History of leap years

The idea of ​​leap years goes back to 45 BC, when the ancient Roman Emperor Julius Caesar established the Julian calendar, which consisted of 365 days divided into 12 months that we still use in the Gregorian calendar.
The Julian calendar included leap years every four years without exception, and was synchronized with Earth's seasons thanks to the "Last Year of Confusion" in 46 B.C., which included 15 months with a total of 445 days, according to the University of Houston.

For centuries, the Julian calendar seemed to work perfectly, but by the mid-10th century, astronomers noticed that seasons were starting about XNUMX days earlier than expected when important holidays, such as Easter, no longer aligned with certain events, such as the vernal equinox.

To remedy this problem, Pope Gregory XIII introduced the Gregorian calendar in 1582, the same as the Julian calendar but excluding leap years for most centennial years.

For centuries, the Gregorian calendar was used only by Catholic countries, such as Italy and Spain, but it was eventually adopted by Protestant countries as well, such as Great Britain in 1752, when its years began to deviate significantly from those of Catholic countries.

Because of the discrepancy between the calendars, countries that later switched to the Gregorian calendar were forced to skip days to synchronize with the rest of the world. For example, when Britain switched calendars in 1752, September 2 was followed by September 14, according to the Royal Greenwich Museum.

The Live Science report concludes that humans will be forced at some point in the distant future to reevaluate the Gregorian calendar because it does not correspond to solar years, but it will take thousands of years for this to happen.

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