Somerset Times

A Leap of Faith




Somerset Times Edition

Week 4,
Term One, 2016

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At the end of the month, an extra day is added to the calendar to incorporate 29 February. This means that 2016 will be comprised of 366 days, making it a leap year.

The reason for the adjustment is to do with the rotation of the earth around the sun, or for those pre-Copernicans amongst us, the rotation of the sun around the earth. An ‘ordinary’ year contains 365 days but the period of the earth’s orbit is roughly 365 and a quarter days, so if there was no adjustment, the seasons would be displaced by about one day every four years.

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Julius Caesar reformed the calendar in 46 BCE after consulting with the Greek astronomer Sosigenes of Alexandria. Until then, the Romans had a more complicated system to keep pace with the required correction; they alternated years of 355 days with years containing an extra, intercalary month of either 22 or 23 days. The Julian calendar, with an extra day every four years, worked well but over the years there was still a slight variation because the earth’s solar orbit actually takes 365.2425 days. By the 16th Century the discrepancy in the dates amounted to ten days and this had practical implications for the Catholic Church and their festivals, especially Easter, which used 25 March in its calculations.

In 1582, Pope Gregory XIII modified the calendar again so that every 100 years would NOT be a leap year unless the number was divisible by 400. The year 2000 was a leap year but 2100 will not be one. This changed the mean calendar year from 365.25 days to 365.2425 days, an error of just 0.002%. The Gregorian calendar then deleted the ten days in 1582 from 5 to 14 October but not all countries adopted this system immediately. In Protestant Britain, it was another 170 years until they came in line with the new Catholic calendar, although by that stage they then had to delete eleven days to catch up.

Sweden made their own adjustment in 1700 by gradually losing 11 days over a period of time but after making a mistake, they corrected it in 1712 by creating a unique 30 February. People born on that day were destined to only ever have one proper birthday celebration and then they would hardly remember it for themselves.

The probability that someone in a population was born on 29 February is 1 in (4 x 365 +1) or 1 in 1461. The Somerset student population has now reached 1490, so by the law of averages there is a good chance that one Somerset student is a ‘leapling’, celebrating their birthday on that day - and we do! Just one student has a birthday on 29 February. Calen Tang in Pre-Prep will be four years old on that day, although it really will only be his first birthday. At that rate of progress, he will graduate from Year 12 when he is four.

Wait a minute! What about a leap second? Last year we added an extra second to the official atomic clocks. This is to allow for the change in the speed of rotation of the earth on its own axis as it slows down (a little bit) due to tidal friction. Since this system was implemented in 1972 a total of 26 leap seconds have been added.

... and for anyone really keen on forward planning, our current Gregorian calendar will need another adjustment in the year 3200.

Calen Tang

Calen Tang
Somerset College’s Leapling

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