The complexities of a solar year

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Tomorrow is New Year’s Day, marking the beginning of a fresh year. Come midnight tonight, we shall kiss goodbye to 2023 and forever consign it to history. There will be ululations, noise making, fire cracking and all manner of audible celebrations to mark the passing of one year and the beginning of another.

What is a year? Perhaps it is not easy to put into words what a year is. It is like an elephant: we cannot adequately define an elephant, but we know one when we see one. Most of us think of a year in terms of seasons. We know that one season has receded and another has started. In Malawi we have two major seasons, namely the dry season and the rainy season. Although we have had no calendar of Malawian origin, yet we know that a year has elapsed when we traverse through both seasons and we start over.

A year is simply a full cycle of the Earth around the Sun. If at a certain point in time the Earth is at position A with respect to the Sun, the period it takes for it to reach that point again as it revolves around the Sun is one year. This is called a solar year. The adjective solar is derived from the Latin word Solaris, which simply means the Sun.

The calendar we use in this part of the world today has been bequeathed to us by the Romans. The earliest Roman calendars were not based on solar years but on lunar ones. The adjective lunar is derived from another Latin word, luna, which means the Moon. So a lunar year is one that is based on the cycles of the Moon.

The lunar year had 354 days, which is 11 shorter than the number of days in a normal solar year. One of the implications of maintaining the lunar year is that, over time, the year and the seasons will shift out synchronization. If, for example, your rainy season lasts between November and April, you would begin to notice that the season is gradually shifting to later months if you were using the lunar calendar. At some point, the wet season months would be characterized by dry weather and vice versa. Obviously, this would be confusing to everybody, not least to the agriculturalists and the planners.

During the reign of the famous Emperor Julius Caesar, the Romans abandoned the lunar year and adopted a solar one instead, thereby introducing what became known as the Julian calendar, after the Emperor. Not only did the Julian deal with the lack of synchronization in the lunar calendar, it also began to have leap years to take into account the fact that it does not take exactly 365 days for the Earth to complete one revolution around the Sun but 365¼ days. It does not take extraordinary mathematical prowess to realise that after every four years, an extra full day will be created, resulting from the cumulative effect of the additional quarter of a day we have in every solar year. After some years, a 365-day year would still lead to lack of sychronization between seasons and years. To avoid this discrepancy, Julius Caesar introduced an extra day every four years in the Julian calendar. Such a year is called a leap year. In a leap year, which 2024 will be, February ends at 29 and not 28. It is for the reasons described in this paragraph that the Julian calendar carried an extra day every four years.

In 1582, Pope Gregory XIII reformed the Julian calendar further. This was after the Julian calendar had been in use for 1600 years. Gregory’s reforms came after it had been observed that even with the introduction leap years, the number of days in a year was still incorrectly stated, albeit by a wee bit. This was noted after astronomers carefully estimated the number of days the Earth took to complete its revolution around the Sun to be 365.2425 days and not exactly 365.25 days, which resulted in a slightly longer year. Gregory, therefore, changed the formula by which leap years were calculated. Previously, any year divisible by 4 would be a leap year. By Gregory’s formula, years that were divisible by 100 but not by 400 would not be leap years even though they would be divisible by 4. The year 1900, for example, was not a leap year although the number 1900 is divisible by 4. After 2096, which will be a leap year, the next leap year will not be until eight years later, as 2100 will not be a leap year.

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