Frankfurt (Germany) – The International Earth Rotation and Reference Systems Service (IERS) will add a leap second to 2008. The first one added since 2005, and the 24th added since the service began in 1972, the last day of the year will be 23 hours, 59 minutes and 61 seconds long.
The IERS reports that no leap seconds were added between the years 1998 and 2005 due to “a slight, temporary acceleration in the Earth’s rotation.” These are caused by the moon and other planets pulling on the Earth very slightly. They accelerate or decelerate the Earth’s rotational speed. These changes in speed also occur unevenly, necessitating the 2nd leap second in just three years. The system is capable of introducing as many as two leap seconds a year, one at the end of June and the other at the end of December.
The leap seconds are added to the UTC time, which is maintained by atomic clocks. Atomic clocks are accurate to billionths of a second and can detect differences in the Einstein curvature of space-time when on the surface of the Earth compared to low Earth orbit (which contains a barely detectable lower gravitational field). Note: astronauts in low-Earth orbit are not actually experiencing a lack of gravitation which induces their weightlessness. They are subject to nearly 100% of the Earth‘s full gravitational field, but are falling toward the Earth at the same rate they are moving around the Earth.
No updates required
Those using automated Internet-based time services to maintain their computer or PDA clock will be unaffected as this system is designed to automatically distribute the leap second throughout the network. Cell phone networks will also be automatically updated. Manual intervention may be required to adjust grand daddy wall clocks, however.
In 1820, the standard of 24 hours per day, 60 minutes per hour and 60 seconds per minute was created. It wasn’t until the 1950s when atomic clocks began to be far more reliable timekeeping sources than any other method known to man. In 1958, the International Atomic Time (TAI) scale was created, which is maintained by an uninterrupted series of atomic clocks positioned around the Earth.
Universal Time 1 (UT1) was also adoped at that time to replace Greenwich Mean Time as the standard definition of time. It uses the position of the sun for more accuracy.
Since the establishment of these two systems, which were roughly in sync with each other in 1958, UT1 is now 32 seconds behind TAI due to the slowing of the Earth’s rotation.
In 1971, Coordinated Universal Time (UTC) was adopted with some requirements, namely that the two never be more than 0.9 seconds apart. As a result, leap seconds are periodically added to our time scales.
If polled, most people would tell you that there is a leap year every four years. However, that is not accurate. Leap years occur every 4th year except in centuries not evenly divisible by 400. This means the last century that had a leap-year prior to 2000 was 1600. There were no leap years in 1700, 1800 or 1900.