Saturday, December 20, 2008

The longest year since 1992

Dali and the Persistence of Memory
Image Credit: Salvador Dali /

Does it feel like this year has gone on a lot longer than normal? Granted, now that we are all realizing that we aren't ready for the holidays, it is positively rushing toward its end. And maybe the sense of a long year is just due to the exceptionally long presidential election combined with a total meltdown of the world economy. The bad news on the latter topic just refuses to end.

But if it seems like this year has been longer than normal, you are right! Don't forget, it was a leap year, so it had an extra day. But even this year is long for a leap year, because an additional leap second has been added. The poor, drunken souls in New York City's Times Square will have to hang on one extra second before ushering in 2009.

The need for leap seconds arises from the fact that, as diurnal creatures, our internal clocks are tied to the position of the sun in the sky. We therefore set up our clocks to try and mimic the 24-hour cycle of the sun in the sky. Astronomical observatories, such as the Royal Observatory in Greenwich, England, took careful observations of the sun and stars in order to keep time. They learned that the Earth's rotation was not constant, but tended to change from year to year, and was in fact slowing down, albeit very slowly, over time. But since time was based on the sun, this didn't really cause a big problem.

As machines became an integral part of society, time became important for machinery as well as for people. And for many things (like satellites and computers), the position of the sun on Earth is not relevant. It became more important to define time in a way that was not dependent on the vagaries of Earth's rotation. So the second was defined in terms of physical constants; specifically, a second is defined in terms of the radiation emitted by a specific process in cesium atoms at a temperature of absolute zero. Since a minute is 60 seconds, an hour is 60 minutes, and a day is 24 hours, the "day" according to computers and atomic clocks is now independent of how fast the Earth is spinning. And, a spaceship far from Earth could keep perfect time without staying in contact with Earth.

But since the "official" day is now independent of the actually spinning of the Earth, the two tend to drift apart, with the Earth spinning slower than the real second. So, a commission of geologists and astronomers gets together a few times a year to decide if a leap second needs to be added at the end of June or the end of December.

This year we get a leap second at the end of December. It's the first time a leap second has been added to a leap year since 1992. So, 2008 is indeed the longest year in 16 years. Since better things are hopefully ahead next year, we'll just have to be an extra day and one second patient for this year.

There is some talk about getting rid of leap seconds, and waiting until a full hour is needed (which would be about 3000 years from now) before adding in a leap hour. The arguments for abolishing leap seconds are that they are somewhat tricky to deal with when dealing with computer programs and operation. The arguments against abolishing a leap second include that it makes life a little harder for us astronomers (since finding objects in the sky requires precise knowledge of the time), and eventually it means that, in a few thousand years, the sun will appear to be behind by about an hour (and isn't it already dark enough when you wake up on these long winter nights?). And there are already time systems available (like GPS time and international atomic time. Frankly, none of the arguments for either side have been really compelling to me. I think we as humans are pretty able to either adapt our computers or our lives to whatever time system we choose.

So, try and enjoy your extra second this year!

1 comment:

  1. The earth rotates at @1000 mph at the equator w to e. That is the current explanation. A plane that lifts off at the equator flying w to e must be able to fly faster than 1000 mph to advance across the surface of the earth. Most commercial jets fly @500 mph. The jet is moving at half the speed of the surface of the earth. How can the jet advance then along the surface of the earth...unless the earth is NOT rotating.