Wednesday, December 24, 2008

On the First Day of Newton, My True Love Gave to Me

There is a delightful column yesterday by Olivia Judson in the New York Times called "The Ten Days of Newton". (Browsers of this blog are familiar with her column "The Wild Side" and some of her writings on evolution in that forum.)

In this column, other than her light-hearted advocacy for the celebration of 10 days of Newton around Christmas and a very cogent summary of Newton's mind-boggling contributions to science, she has a wonderfully informative discussion on the development of our calendar which has continually had to account for the fact that the earth's orbit around the sun is not an exact number of days. I found her discussion of the earth's gradual slowing down and the impact on adjustment of calendars absolutely fascinating.

And for all those who come across this blog I wish you all a happy holiday season and a happy new year. I, for one, would certainly second Olivia Judson's call for a celebration of the achievements of Newton. Her song (sung to the tune of 12 days of Christmas) is not likely to catch on in the same way but it is good fun anyway.

On the tenth day of Newton,
My true love gave to me,
Ten drops of genius,
Nine silver co-oins,
Eight circling planets,
Seven shades of li-ight,
Six counterfeiters,
Four telescopes,
Three Laws of Motion,
Two awful feuds,
And the discovery of gravity!


The reason the interval became necessary is that the Earth, inconveniently, does not orbit the sun in an exact number of days. Instead, the Earth’s orbit is 365 days and a bit. The “bit” is just under a quarter of a day.

It wasn’t always thus. Some 530 million years ago, when animals like the trilobites were skittering around, days had less time. Back then, a day was only 21 hours, and a year was about 420 days. In another 500 million years, perhaps a day will be 27 hours, and a year fewer than 300 days. Because of the friction exerted by the moon, the Earth is slowing down. Indeed, already the days are a tiny bit longer than they were 100 years ago.

Because the orbit isn’t an exact number of days, our calendars get out of sync with the seasons unless we correct for the fractional day. The Julian calendar, which was put in place by Julius Caesar in 45 B.C., was the Romans’ best effort at making a systematic correction. Before that, the Roman calendar gave 355 days to the basic year, and every other year was supposed to include an extra month of 22 or 23 days.

But over a period of 24 years, that gave too many days; so in some years, the extra month was supposed to be skipped. This didn’t always happen. By the time the Julian calendar was introduced, the Roman calendar was so far out of sync with the seasons that the year before the first Julian year had to include a massive correction; that year, referred to as “the last year of confusion,” was 445 days. Talk about a long year.

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