Once again, history proves to be an important asset for humankind. Astronomers have carried out a study by collecting useful data from hundreds of ancient eclipses that had ever shadowed the Earth. The oldest recorded eclipse comes from the 8th-century B.C.E. They noticed one thing for sure, and that is that Earth’s spin has been slowed down for ages.
The study paid attention to the dates and places of eclipses from ancient Greece, the Middle East, China and other areas. This is how scientists noticed a discrepancy between reality and the results of their mathematical calculations. Based on their equations, one of the total solar ancient eclipses that happened in 720 B.C.E. was supposed to take place in the western Atlantic Ocean and not in Babylon (which today is Iraq). This unusual difference can mean one thing, and that is that the numbers have changed over time.
By studying this phenomenon, scientists discovered that 2740 years ago, one day lasted for 18 hours. The fact that nowadays it takes 24 hours till dawn is the direct result of a slower rotation of the Earth. By their calculations, one century added 1.78 milliseconds to the length of a day.
Ocean tides are playing a crucial role in this process. The seas are slamming the Earth’s continents causing the planet to lose some rotational momentum. However, when researchers took only this factor into consideration, they realized that the day should have gotten bigger than it is. Consequently, there are other agents that take part in this phenomenon.
The last ice age altered the constitution of the Earth, causing it to gather additional massive ice sheets. The ice has melted away by now, but the crust is slowly rebounding. At high altitudes, the crust springs upward. At low altitudes, Earth is shrinking inward. This effect influences the rotation of the planet to happen at a slower pace than usual.
Thanks to this discovery, the scientists are able to predict the following eclipses precisely. The next one should shadow a large part of United States on 21st August 2017. The new data will also help scientists understand better the movement of liquid iron from the outer core which is responsible for Earth’s magnetic field.
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