Earth's Rotation
The Earth rotates in a period of slightly less than 24 hours on an axis that runs between the North and South Poles. The east-west circumference of the Earth decreases as the latitude increases. The rotational speed is 1,038 miles per hour (1,670 kph) at the equator, 519 mph (835 kph) at 60° and 0 at the poles (90°).
Standing on the Earth's surface, it appears that the planet is fixed and the rest of the universe is revolving around it. For a long time, this apparent motion was taken to be real, coupled with the doctrinal belief that man and the Earth were at the center of the universe.
One exception to early thinking was the Greek astronomer Heracleides of the fourth century B.C. who suggested that it might be possible that the Earth was traveling around the Sun. His main clue was the close relationship the inner planets, Mercury and Venus, had with the sun.
The fixed Earth concept survived into the Renaissance period. German astronomer Johannes Müller (1436-1476; known as Regiomantanus) expressed the sentiment of the day when he stated that centrifugal force would cause everything to fly off of a rotating Earth. Attempts to explain away such complications as the independent motions of comets and meteors only led the geocentrists further from the truth.
It was Nicholas Copernicus, the Polish astronomer, who finally put the universe into proper motion, so to speak. He felt that a heliocentric solar system was more logically simple than Ptolemy's geocentric system. His ideas were published in 1543, the year of his death.
Italian astronomer Galileo was an adherent of Copernican thought. After making improvements on the newly invented telescope, he discovered (beginning about 1610) such things as planetary moons, features on the Earth's moon and revolving spots on the Sun's surface. Such findings did not agree with traditional teachings and led to his persecution by the Inquisition.
Galileo had succeeded in sowing the seeds of new thought. In 1664, Isaac Newton began to develop the law of gravitational pull, which not only explained why birds and buildings were not being hurled into space, but also explained the orbits of the planets and made it mandatory that the Earth be rotating.
A much later addition to our knowledge of the Earth's rotation came from American geophysicist William Ferrel. He suggested in the 1850s that perturbations in the gravitational pull on the Earth by the Sun, Moon and other heavenly bodies cause the Earth 's axis to wobble, which is now an accepted fact.
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