Saturday, June 24, 2017

Ugarit Total Solar Eclipse

Trivia: The Ugarit Total Solar Eclipse

In 1948, a clay tablet was discovered in the port city of Ugarit in Northern Syria. In the text of the tablet, a Mesopotamian historian noted, "On the day of the new moon, in the month of Hiyar, the sun was put to shame, and went down in the daytime, with Mars in attendance." Scientists realized the text described a total solar eclipse in which the planet Mars was visible during totality.

Researchers originally dated the eclipse event as May 3, 1375 B.C. But further study suggested a different eclipse. Researchers considered the dating of the tablet, combined with the text's statement of the month in which the eclipse occurred and the fact that Mars was seen during totality. This evidence pointed to the total eclipse of March 5, 1223 B.C. The revised findings were first published in 1989 in the journal Nature.

The Ugarit eclipse is one of the earliest solar eclipses recorded. The path of totality began in the Atlantic Ocean, crossed north-western Afrca, Turkey, and central Asia.

The Accelerating Moon, the Decelerating Earth

The dating of ancient solar eclipses provides astronomers with reference points to determine long-term evolution of angular momentum in the Earth-Moon system--that is, it helps astronomers understand how the moon's orbit and Earth's rotation have changed over time. The revised date--March 5, 1223 B.C.--implies that the secular deceleration of Earth's rotation has changed very little during the past 3,000 years.

Secular What?

Ocean tides are caused by the gravitational pull of the moon (and, to a lesser extent, the Sun). The resulting tidal bulge in Earth's oceans is dragged ahead of the moon in its orbit due to the daily rotation of Earth. As a consequence, the ocean mass offset from the Earth-Moon line exerts a pull on the moon and accelerates it in its orbit. Conversely, the moon's gravitational tug on this mass exerts a torque that decelerates the rotation of Earth. The length of the day gradually increases as energy is transferred from Earth to the moon, causing the lunar orbit and period of revolution about Earth to increase.

You can learn more about secular acceleration from the following NASA article.


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