Why we need a leap year: astrophysicists explain extra day in February 2024

The 29th day occurs in February every four years, and there is such a long month in 2024.

2024 is a leap year, but some people don’t know what that actually means. Why are there 29 days in February instead of 28 days in a leap year? Phys, astrophysicists Minjae Kim and Dr. from the University of Warwick in England. He writes that James McCormack explains the essence of this phenomenon.

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According to Kim, leap years are critical for aligning our calendar with the Earth’s orbital motion around the sun. The duration of a complete rotation of our planet around the Sun, also called the tropical year, is approximately 365.24 days. Accordingly, this value is slightly more than the number of days in the standard calendar consisting of 365 days. Although only a quarter of a day may seem like a small increase, over time it leads to a noticeable change in the calendar

If this extra time is not taken into account, the normal calendar will be out of sync with the astronomical seasons, leading to significant shifts over many years, Kim said. Leap years are needed to prevent this shift and keep the standard calendar consistent with the Earth’s journey around the Sun.

To avoid any inconsistencies, one more day is added to the 29th of February every four years. This simple solution to the problem was perfected in the Gregorian calendar, the most used calendar system on earth.

According to McCormack, leap years were introduced into the calendar system in ancient Roman times, when the year was divided into 12 months and 365 days. In 46 BC, Julius Caesar proposed a new Julian calendar that added one more day to February, the shortest month of the year. One day had to be added every 4 years; This was supposed to provide a predictable fix for the quarter day offset issue.

But in reality there was an overcorrection. After all, the solar year does not last exactly 365.25 days, in fact it lasts a little less – 365.2422 days. Therefore, the Julian calendar and the solar year no longer deviated from each other by that much, but by about 11.2 minutes per year.

By the end of the 16th century, this caused the calendar to deviate from the solar year by 13 days. Therefore, Pope Gregory XIII initiated a calendar reform in 1582 and introduced the Gregorian calendar, which modified the Julian calendar to accommodate the 11.2-minute shift.

According to McCormack, the Gregorian calendar skips 3 leap days every 400 years to ameliorate the excessive adjustments made by the Julian calendar. Therefore, the average length of the year is 365.2425 days, which is closer to the length of the solar year – 365.2422 days.

Scientists say leap years are an indication of how humans have been able to reconcile Earth’s concept of time with the natural rhythm of the universe.

As I already wrote FocusA 2000-year-old astronomical calendar was found in a tomb in China. According to archaeologists, the calendar consists of 23 wooden tablets.

Source: Focus

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