Science of Seconds

January 20, 2012

Rheanna Sand


We humans have long measured time by the cyclic movements of our planet. A year is how long it takes to go once around the Sun. A day is how long it takes for the Earth to spin once on it's axis. The Egyptians reportedly divided the day into two 12-hour periods of daylight and darkness (and the hours at first changed length depending on the season, but later were fixed at equal lengths). Greek astronomers divided the fixed hour into minutes based on the sexagesimal (base 60) system, and presumably the minute into seconds.

But with the advent of the atomic clock in 1949, the measurement of time was separated from the rotations of the Earth on its axis and around the Sun. Though imperfections in these rotations were known for some time, it was not a problem until official timekeeping for scientific purposes became reliant on the atomic clock. In short, the two types of clocks, astronomical and atomic, are out of sync.

In so-called "leap years," we add a day to February to make up for the fact that going around the sun takes 365.25 days. Similarly, scientists have created the "leap second" which they add about once a year to atomic clocks to make up for the imperfect rotation of the Earth. But adding a second to machines and computers that rely on a continuous measurement of time is not trivial. So, the International Telecommunications Union held a meeting in Geneva yesterday to decide what to do about the leap second. The United States, Japan, Italy, Mexico, and France want to scrap it, but the U.K., Canada, and Germany want to keep up the practice.

Despite the large amount of support for getting rid of them, the group decided to table the issue until 2015. In other words, the leap second bought itself some time.

Here is an excellent video from Al-Jazeera English explaining the concept of leap seconds and the two sides of the debate.




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