- Leap years are 366-day years in which a normally 365-day calendar year is replaced by 29 days in February every four years.
- This year, there will be another leap year as February will have 29 days.
- Leap years are basically meant to coincide with one calendar year as one orbit of the Earth around the Sun.. However, with leap year calculations, a calendar year does not exactly correspond to one year of the Earth around the Sun.
This year, February will be a leap year that comes every four years, as it will have 29 days. So why do leap years exist and why do we need them in calendars?
Leap years are years that have 366 calendar days instead of 365. Leap years occur every four years in the Gregorian calendar used by most of the world. Except for some centennial years (for example, 1900) or years ending in “00”, every year that is divisible by four, such as 2020 and 2024, is a leap year. In calendars, the same date advances only a single day between successive years. In leap years, starting from March, each date of the leap year advances one extra day compared to the previous year. That’s why these years are called “leftover”. For example, in 2023, March 1 fell on a Wednesday, but in 2024 it will fall on a Friday.
Other calendars also have leap year versions, including the Hebrew calendar, Islamic calendar, Chinese calendar, and Ethiopian calendar. However, not all of these leap years come every four years and they usually occur in different years than those in the Gregorian calendar. However, some calendars also have multiple leap days and even shortened leap months. In addition to leap years and leap days, the Gregorian calendar also has a handful of leap seconds occasionally added to certain years, most recently in 2012, 2015, and 2016. However, the International Bureau of Weights and Measures (IBWM), the organization responsible for global time management, will eliminate leap seconds from 2035. Last week, an international coalition of scientists and government agencies voted to retire the timekeeping system, which will officially expire in 2035.
Why do we need leap years?
At first glance, all this excess may seem unnecessary someday. But these leap years are very important, and without them the years would be very different. How Does? Leap years exist because a single year in the Gregorian calendar is slightly shorter than a solar year or tropical year. One calendar year roughly corresponds to the Earth completing its rotation around the Sun. However, a solar year equals 365.24 days or 365 days, 5 hours, 48 minutes and 56 seconds. In short, leap years mean that the Gregorian calendar remains in sync with our journey around the sun.
Discounting this difference, for each year that passes, the difference between the beginning of a calendar year and the beginning of a solar year widens by 5 hours, 48 minutes and 56 seconds, and over time this changes the timing of the seasons. For example, if we stopped using leap years, according to the National Air and Space Museum, in about 700 years the Northern Hemisphere’s summer would begin in December instead of June. This is where leap years come into play, because an extra day added every four years is approximately the same length as the difference accumulated over that period. But the system is not perfect. With leap years, we gain about 44 minutes extra every four years, or one day every 129 years. To solve this problem, we skip leap years in every centennial except those divisible by 400, such as 1600 and 2000. But even then there is still a small difference between calendar years and solar years. Leap seconds, which were planned to be abolished by 2035, were also used to eliminate this small difference.
The history of leap years dates back to B.C., when the Ancient Roman emperor Julius Caesar introduced the Julian calendar, which was divided into 12 months and consisted of 365 days. It dates back to 45 years ago. The Gregorian calendar we currently use still uses the same system, with a small adjustment. According to the University of Houston, the Julian calendar included leap years every four years without exception. B.C. Thanks to the “last year of confusion” in 46 BC, which lasted a total of 445 days and included 15 months, a calendar year was synchronized with the Earth’s seasons.
For centuries, the Julian calendar appeared to work perfectly. But in the mid-16th century, astronomers noticed that the seasons began about 10 days earlier than expected because important holidays such as Easter no longer matched certain events such as spring or the vernal equinox. To correct this, Pope Benedict XIII. Gregory introduced the Gregorian calendar in 1582, which was identical to the Julian calendar but excluded leap years for most centenarians.
For centuries, the Gregorian calendar was used only by Catholic countries such as Italy and Spain. However, since the other years used began to deviate greatly from the years of Catholic countries, they were also adopted by Protestant countries such as Great Britain in 1752. Due to the inconsistency between calendars, countries that later switched to the Gregorian calendar had to skip days to synchronize with the rest of the world. For example, when England changed calendars in 1752, September 2 was followed by September 14, according to the Royal Museums in Greenwich.
At some point in the distant future, the Gregorian calendar may have to be reevaluated because it is out of sync with solar years. However, it will take thousands of years for this to happen.
Compiled by: Fatma Ebrar Tuncel