If June 30 seems a little longer than normal, that will be because an extra second is being added to the day to account for the orbital mechanics of our planet. As the Earth orbits around the sun, our planet is rotating more slowly, which needs to be accounted for by the addition of leap seconds.
A normal day is supposed to last 86,400 seconds, as measured by atomic clocks. These timepieces, based on the decay of cesium, are accurate within one second every 1.4 million years. Leap seconds are required, from time to time, to allow atomic clocks to stay in sync with the actual motion of our home planet.
Motions of the Earth, moon, and sun work together to slow the rotation of the Earth, lengthening our days. Due to these, the mean solar day (the amount of time it takes the sun to appear in identical places in the sky) is currently 86,400.002 seconds, roughly 2/1000 of a second longer than it was in 1820.
This difference may seem tiny at first, but over the course of a year, that error could add up to more than two-thirds of a second. Due to the complex interactions of the Earth/moon/sun system, the exact length of the day is impossible to predict with certainty. Other factors which influence the length of the day include dynamics of the core of the Earth, movement of the oceans, and the presence of ice.
Just before midnight on June 30, the bizarre time of 11:59:60 will show on clocks, providing an extra second to the day. When leap seconds are required to re-synchronize atomic clocks, the extra time is usually added on either June 30 or Dec. 31. The first leap second was added in 1972, although corrections were required before that time.
"In the short term, leap seconds are not as predictable as everyone would like. The modeling of the Earth predicts that more and more leap seconds will be called for in the long term, but we can't say that one will be needed every year," said Chopo Ma, a geophysicist from the Goddard Space Flight Center and a member of the directing board of the International Earth Rotation and Reference Systems Service.
The last time this occurred, many computers crashed, especially those running Linux as their operating system. Electronic check-in and reservation systems at Quantas Arlines went down, forcing workers to record customer information by hand.
Email systems can be affected, as any message received during the leap second could be deleted, since its timestamp is one that would normally be in error. Computers also need to carry out some regular operations once a second. When internal processors record a minute with 60 seconds added on, it can create havoc, crashing many systems.
The leap second due on June 30 is unlikely to cause major problems, although the event could affect some people and companies who rely on electronic devices.
Photo: HalfRain | Flickr
