Introduction
A leap year is a year that has an extra day added to it, making it 366 days instead of the normal 365 days. The additional day is added to February 29th and occurs once every four years (Saelee et al., 2018). The reason why leap years are necessary has to do with the time it takes the Earth to revolve around the Sun.
Discussion
It takes approximately 365.2422 days for the Earth to completely go around the Sun and not exactly 365 days (Saelee et al., 2018). To account for this discrepancy, an additional day is added to the calendar every 4 years, bringing the total number of days in the calendar year closer to 365.2422 days (Saelee et al., 2018). Without leap years, the calendar would gradually become out of sync with the astronomical year. For example, without the introduction of leap years, the dates for important astronomical events, such as solstices and equinoxes, would gradually shift out of their correct positions on the calendar. This could lead to significant inaccuracies over time.
The Julian and Gregorian calendars approach leap years differently. The Julian calendar, introduced by Julius Caesar in 45 BCE, added an extra day every four years (Kumaar, 2022). Nonetheless, the accuracy of this formula was challenged as the Earth’s rotation around the Sun takes slightly less than 365.25 days. This caused the calendar to become gradually out of sync with the astronomical year. To address this issue, Pope Gregory XIII introduced the Gregorian calendar in 1582 (Kumaar, 2022).
Conclusion
The calendar modified the calculation method of leap years by considering a year as a leap year if it is divisible by 4, except if it is divisible by 100 but not by 400 (Kumaar, 2022). This formula allows for a more precise determination of when a leap year should occur, taking into account the small difference between the Earth’s orbit and the calendar year.
References
Kumaar, S. S. (2022). Chronology of calendar: Human evolution journey. International Journal of History, 4(1), 17–22. Web.
Saelee, C., Tawonatiwas, M., & Yodintra, S. (2018). Suvarnabhumi-Gregorian rule to determine whether Thai lunar calendar year 2012 is a leap-month year. Chiang Mai Journal of Science, 45(6), 1-18. Web.