The city of Madrid was abuzz with the unique phenomenon that only happens every four years – the appearance of February 29 on the calendar. This year, the special day fell on Thursday, the 29th of February 2024. This occurrence is more than just an oddity, it serves to rectify the periodic inconsistencies that occur in our calendar system.
Generally, each year comprises 365 days. However, what is often overlooked is an additional 5 hours and 48 minutes that are not accounted for. Consequently, every four years, an extra day – February 29 – is included, making that year a 366-day year.
The term “leap year” is derived from the Latin phrase “bis sextus dies ante the heat of March”, which translates to “the sixth day before the month of March”. This refers to an additional day that Julius Caesar inserted between February 23 and 24 in the Julian calendar.
This was due to the fact that in the Julian calendar, February 24 was considered six days before the calends (the first day) of March. The Romans had a unique approach to counting the days of the month. Instead of counting from the first day to the last, they used three reference points: hot, nine and idus. The reference day was included in the count (in this case, March 1).
Fast forward to the implementation of the Gregorian calendar by Pope Gregory XIII, which is the calendar system we use today. In this system, the extra day was moved to the end of February, thus giving the month 29 days instead of the usual 28.
The Rules
The determination of a leap year is governed by certain rules
. In the Julian calendar, any year that could be evenly divided by four was considered a leap year. In the Gregorian calendar, the rule is slightly more complex. A year is deemed a leap year if it is divisible by four, unless it is also divisible by 100. However, if the year is divisible by 100 and 400, it is still considered a leap year.
Experts have clarified that this rule effectively eliminates years that mark the end of each century (those ending in 00) unless the century itself is a multiple of four.
The concept of the extra day in a leap year dates back to 49 BC. Julius Caesar, during his visit to Egypt, discovered a superior calendar system in the lands of the Egyptian pharaoh Cleopatra. The Roman calendar, in comparison, was filled with inconsistencies. Caesar then entrusted Sosigenes of Alexandria, a renowned astronomer, mathematician, and philosopher, with the task of creating what is now known as the Julian calendar.
The Julian calendar had a duration of 365 days and included an extra day every four years. This was to compensate for the natural lag caused by the Earth’s non-synchronous revolution around the Sun. The correction of the imbalances that had accumulated in the Roman calendar resulted in the longest year in history in 46 BC – lasting a whopping 445 days. This was done to reset the calendar and start afresh. This year came to be known as the Julian year
or the year of confusion
according to Wikipedia.
The Egyptians were already aware that every four years, the heliacal rise of the star Sothis (Sirius) was delayed by one day, marking the start of a new year. However, despite having the opportunity to implement this reform two centuries earlier at the Council of Canope, the Egyptians failed to do so due to conflicts between the priestly and political classes.
This calendar remained the official calendar in Rome for centuries to come. Even at the Council of Nicaea, Sosigenes’ error was acknowledged, but no steps were taken to correct it. It wasn’t until 1582 that the Gregorian calendar was adopted.
