The Time Of One Rotation Of The Earth Is Not 24 Hours
And MC Should Use The Following Method
HOW DO WE OBSERVE EARTH ORIENTATION?
In order to observe Earth orientation, observations must be made from the Earth of objects located in space. Objects that are used include stars, artificial satellites, the Moon, and distant radio sources called quasars. These provide useful reference directions with which to measure the Earth's orientation.
To determine the Earth's orientation very accurate observations of these objects must be made. Stars have been observed photographically for decades to determine the motion of the pole and the rotation of the Earth. Recently, more accurate methods have been devised including the use of lasers and radio telescopes. Laser bursts can be bounced off of artificial satellites or the Moon. This provides information on exactly where the satellite is at a particular time which, in turn, can be used to determine the Earth's orientation in space.
Radio telescopes can also be utilized in a technique called Very Long Baseline Interferometry (VLBI). By having several radio telescopes looking at the same quasar at the same time and recording the information that is seen at each telescope, the Earth's orientation can be determined. USNO operates a VLBI network for this purpose. The recorded information then needs to be processed further before the final results can be determined. The reduction procedure involves the use of a highly specialized computer called a correlator. Currently, there are three such correlators in the United States, one located at USNO, one in Boston (Haystack Observatory), and one located in Socorro, NM. Once the data from a VLBI experiment has been correlated, it can be processed further to produce Earth orientation information.
Astronomical observations are made routinely by a number of observatories located around the world for this purpose. The IERS is the international organization responsible for the coordination of observations of polar motion and nutation as well as astronomical time. The Central Bureau is located at the Paris Observatory. Sub-bureaus devoted to rapid service and predictions and atmospheric angular momentum are located at the U. S. Naval Observatory and Atmospheric and Environmental Research, Inc. respectively. Observations are contributed to the IERS by observatories and laboratories around the world and treated at analysis centers. The IERS Sub-bureau for Rapid Service and Predictions then combines these data into a series of x, y, UT1-UTC, and celestial pole offsets. This information is recomputed twice per week (usually Tuesday and Thursday) and disseminated by e-mail, anonymous ftp and the world wide web.
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http://www.physics.uoguelph.ca/summer/scor/articles/scor42.htm
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