The new year has just arrived, and it happens to be a leap year with 366 days. That said, what exactly are these years, and why are they different?
Leap Years
Unlike years with a typical 365 days, leap years have 366 days. These years take place every four years in the Gregorian calendar, which is used across the majority of the world. This added day, called leap day, is February 29. This day is not present in non-leap years.
Each year that can be divided by 4, such as 2024 and 2020, is a leap year. The exception to this is some centenary years, which end in 00.
Leap years have been called "leap" years due to how, from March onwards, each leap year date moves forward by one day further compared to the year before. For instance, in 2023, March 1 fell on a Wednesday. However, in 2024, it will be a Friday. In normal cases, the same date will only move forward by one day in the coming years.
Other types of calendars, including the Islamic calendar, Chinese calendar, and Hebrew calendar, have their own kinds of leap years. However, these do not come every four years. They also typically occur in other years than those of the Gregorian calendar.
On top of having leap years and leap days, the Gregorian calendar also has some leap seconds, which have been included sporadically in certain years. The most recent cases were in 2016, 2015, and 2012. However, according to the organization that handles global timekeeping, the International Bureau of Weights and Measures (IBWM), leap seconds will be abolished in 2035 and beyond.
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Why Leap Years Are Important
While leap years may seem like a silly addition, they actually hold grave significance. These years exist due to the fact that the Gregorian calendar's single year is a bit shorter compared to a tropical or solar year, which refers to the time it takes for the Earth to finish rotating around the Sun.
A year in the calendar typically takes 365 days, but a solar year comprises 364.24 days, which is equivalent to 365 days, 5 hours, 48 minutes, and 56 seconds.
If this difference was not accounted for, then for each passing year, the gap between the calendar year's start as well as the solar year will get wider by 5 hours, 48 minutes, and 56 seconds.
As time passes, the timing of the seasons will end up shifting. For instance, if leap years were no longer used, then in roughly 700 years, summer in the Northern Hemisphere would start in December and not June.
Including leap days every four years largely addresses this concern, as the extra day is roughly equivalent to the same length as the accumulating time differences.
While the system is quite innovative, it is not perfect. Because of it, every four years, an extra 44 minutes are gained. This is equivalent to an extra day every 129 years.
In order to address this issue, leap years are skipped each centenary year, except for those that can be divided by 400. Even still, a small difference between calendar and solar years exists, which is why the leap-second experiments were included.
Generally, leap years refer to how the Gregorian calendar tries to remain in sync with the Earth's orbit around the Sun.
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