| Official timekeepers add one second to 2008 |
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| by William Atkins | |
| Monday, 29 December 2008 | |
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These leap seconds are used occasionally because the Earth slows its spin (rotation) about its axis by an average of two-thousandths of a second (two milliseconds) each day. This slowness occurs primarily because of gravitational forces acting on the Earth from the Moon and from other secondary sources such as heavy movements deep within the interior of the Earth. The organization called the International Earth Rotation and Reference Systems Service (IERS), with its central bureau located in Frankfurt, Germany, takes care of time with respect to Earth’s spin about its axis. It is the responsibility of the IERS to make the decision to add a leap second to the world's official clocks. The IERS assures that atomic clocks do not vary by more than 0.9 seconds with respect to the Earth’s rotation. When they vary by more than 0.9 seconds, they order a new leap second to be introduced around the world. These atomic clocks are used to tell time by the vibration of very accurate cesium atoms. These clocks are accurate to within one billionth of a second each day, and are much more accurate than clocks that use the rotation of the Earth. Thus, these atomic clocks are used as the official timepieces for the official timekeeper for the world Page two continues. |
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