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Uranus.

Since prehistoric times, human beings had been aware of the five bright starlike planets: Mercury, Venus, Mars, Jupiter, and Saturn. With the coming of Copernican principles (see 1543), Earth itself became a sixth, coming between Venus and Mars. It seemed somehow impossible that there could be another. Surely, if there were another, it would have been seen.

In the 1770s, a British astronomer (of Hanoverian birth) began studying the heavens. He was William Herschel (1738-1822). A music teacher by profession, he had grown interested in astronomy. Unable to buy a telescope he considered sufficiently good, he took to grinding his own lenses and mirrors and ended with the best telescopes of his time.

He determined to study, systematically, everything in the sky, and on March 31, 1781, he came across an object that appeared as a disc instead of as a mere point of light. He supposed it to be a comet, but the disc had sharp edges like a planet and wasn't fuzzy as a comet would be. Furthermore, when enough observations had been made to calculate an orbit, he found that orbit to be nearly circular, like a planet's, and not elongated, like a comet's.

What's more, it was clear that the object's orbit lay far outside that of Saturn. It was twice as far from the Sun as Saturn was, and no comet could be seen from that distance.

The conclusion was that Herschel had discovered a seventh planet circling the Sun, which because of its great distance did not appears as bright as the others. In fact, it was visible to the unaided eye as a very dim star and had been observed a number of times by people who never suspected it might be a planet. The first had been Flamsteed (see 1676), who had recorded its position on his star map a century earlier and called it 34 Tauri.

After some hesitation, astronomers decided to continue naming planets for mythological characters, and the new planet was named Uranus, after the father of Saturn (Cronos) in the Greek myths.

The discovery of Uranus doubled the size of the Solar System at a stroke. It was further spectacular proof that the ancients had not known everything, and gave astronomers the exciting knowledge that there was more to be discovered in the sky than additional comets.

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Author:Asimov, Isaac
Publication:Asimov's Chronology of Science & Discovery, Updated ed.
Article Type:Reference Source
Date:Jan 1, 1994
Words:389
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