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Penetrating Space & Time Vol.5 : Earth Movement Slows Down

By Unknown - February 10, 2018

Did you know that a day and a night, the time it takes the earth to rotate, in ancient times and now is different?
Earth Movement Slows Down Due To the Influence of Tidal Power of the Moon

An overnight daily time determined by the time it takes for the Earth to perform a rotation on its axis varies. Scientists know the variation through decades of research with the technique of very-long baseline interferometry (VLBI)

Professor F. Richard Stephenson (born 1941) is an Emeritus Professor at the University of Durham, in the Physics department and the East Asian Studies department. His research concentrates on historical aspects of astronomy, in particular analyzing ancient astronomical records to reconstruct the history of Earth's rotation. He has an asteroid named after him: 10979 Fristephenson. His most famous book is Historical Eclipses and Earth's Rotation (Cambridge University Press, 1997, ISBN 0-521-46194-4).Research that has been done with his colleagues LV Morrison revealed that within 100 years, the Earth's rotation speed slowed down to 1.7 milliseconds.

Long research results with VLBI, combined with other fossil-based research, reveal that the Earth's rotation is slowing down. For the slowing of the Earth's rotation is the Tidal Power of the Moon. The moon itself is moving further away from Earth.

Daniel MacMillan of the Goddard Space Flight Center of the US Aeronautics and Space Agency (NASA). reveals that: there is a variation in the day-to-night difference in the Earth's rotation.

An example is an event on June 30, 2015. The day will officially be a bit longer than usual on Tuesday, June 30, 2015, for an extra second, or "leap" second, will be added.

"Earth's rotation is gradually slowing down a bit, so leap seconds is a way to account for that," said Daniel MacMillan of NASA's Goddard Space Flight Center in Greenbelt, Maryland.

Strictly speaking, a day lasts 86,400 seconds. The Coordinated Universal Time, or UTC. UTC is "atomic time" - the duration of one second is based on extremely predictable electromagnetic transitions in atoms of cesium. These transitions are so reliable that the cesium clock is accurate to one second in 1,400,000 years.

However, the mean solar day - the average length of a day, based on how long it takes Earth to rotate - is about 86,400.002 seconds long. That's because Earth's rotation is gradually slowing down a bit, due to a kind of braking force caused by the gravitational tug of war between Earth, the moon and the sun. Scientists estimate that the mean solar day has not been 86,400 seconds long since the year 1820 or so.

This difference of 2 milliseconds, or two thousandths of a second - far less than the blink of an eye - hardly seems noticeable at first. But if this small discrepancy were repeated every day for an entire year, it would add up to almost a second. In reality, that's not quite what happens. Although Earth's rotation is slowing down on average, the length of each day varies in an unpredictable way.

The length of day is influenced by many factors, especially the atmosphere over the periods less than a year. Our seasonal and daily weather variations can affect the length of the day by a few milliseconds over a year. Earths inner core (over long time periods), variations in the atmosphere and oceans, groundwater, and ice storage (over time periods of decides), and oceanic and atmospheric tides. Atmospheric variations due to El Niño can cause Earth's rotation to slow down, increasing the length of day by as much as 1 millisecond, or a thousandth of a second. (more...)

Leap Seconds
To maintain a standard fixed time as well as what happened with Earth, the Moon, and the Sun, the scientist then initiated a leap second in 1972.

The concept, the addition or even can a one-second reduction at certain times so that time remains in sync with the Earth's rotation. Leap second itself comes with the progress of measuring time, especially seconds, more precisely with cesium atoms.

There are some circles who want the removal of leap seconds because it is technologically inconvenient. For example, create a computer system error. But NASA itself predicts that if leap seconds are removed, then, in 500 years, the time on Earth will be different 25 minutes with time according to the actual rotational motion and Earth revolution.

Related Article :

Penetrating Space & Time Vol.1 : Atomic Clock

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