Wait a second!New Year's 2006 will have to wait. An extra second--called a leap second--will be added to the last day of 2005. For thousands of years, people have defined time by Earth's rotation The Earth's rotation is the rotation of the solid earth around its own axis, which is called Earth's axis or rotation axis. The earth rotates towards the east, which can be observed by orientation with a magnetic compass at sunrise. on its axis: A complete rotation around this imaginary line In general, an imaginary line is any sort of line that has only an abstract definition, and does not exist in fact. As a geographical concept, an imaginary line may serve as an arbitrary division (such as a border). marks one day. But Earth isn't spinning as fast as it used to, says Tom O'Brian, chief of the time and frequency division of the National Institute of Standards and Technology National Institute of Standards and Technology, governmental agency within the U.S. Dept. of Commerce with the mission of "working with industry to develop and apply technology, measurements, and standards" in the national interest. . One slowing factor is the moon's gravity. Its pulling force creates a bulge on the part of Earth's surface Noun 1. Earth's surface - the outermost level of the land or sea; "earthquakes originate far below the surface"; "three quarters of the Earth's surface is covered by water" surface that's closest to the moon. As Earth spins, the moon continues to tug on that bulge. The result? A slight slowing of Earth's rotation, and a tiny lengthening of each day. "For example, a day is about one or two thousandths of a second longer now than it was in 1905," O'Brian explains. Each time those added milliseconds approach a full second, scientists add a leap second leap second - Coordinated Universal Time to atomic clocks. These precise clocks are used as a standard for the world's time. |
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