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Post by Chicago Astronomer Joe on Dec 24, 2005 2:17:33 GMT -6
New Year To Arrive One Second Late
Owing to the gradual slowing down of the Earth’s rotation, the International Earth Rotation and Reference Systems Service, based at the Paris Observatory, has announced that 2005 will contain an extra second.
The required leap second will be added at the end of 31st December, thus delaying the arrival of 2006 by one second. Although this will be the 23rd such leap second to be added since its introduction at the end of June 1972, this year’s leap second will be the first for seven years.
Our normal civil, or clock time, is based on Greenwich Mean Time (GMT), the world standard since 1884, which is tied to when the Sun arrives due south at the Greenwich Meridian, the zero line of longitude. The resulting ‘Universal Time’ is based, as has always been the case, on the rotation of the Earth on its axis.
However, the speed of the Earth’s rotation is continually changing: partly due to varying weather patterns and geological disturbances, but more importantly due to the friction of tides raised by the Sun and Moon, which cause a systematic lengthening of the day.
In fact, the day is now about 2 milliseconds longer than it was a couple of hundred years ago. As a result, leap seconds will always be needed if we are to keep ‘clock time’ and ‘Sun time’ in step.
I read a science fiction book where the people advanced about 50 million years into the future. Their day was about 25 hours long, so they added a "witching hour" to each day, dedicated to drinking. Seems like a good idea to me.
If the universe is a ball the size of America, then the solar system is almost as large as the smallest cell in the human body.