Comet. In his own words:
On Tuesday the 13th of March, between ten and eleven in the evening, while I was examining
the small stars in the neighbourhood of H Geminorum, I perceived one that appeared visibly
larger than the rest; being struck with its uncommon magnitude, I compared it to H Geminorum
and the small star in the quartile between Auriga and Gemini, and finding it to be much larger
than either of them, suspected it to be a comet.
Herschel’s care was the hallmark of a great observer; he was not prepared to jump any
conclusions. Also, to be fair, the discovery of a new planet was the last thought in anybody’s
mind. But further observation by other astronomers besides Herschel revealed two curious
facts. For the comet, it showed a remarkably sharp disc; furthermore, it was moving so slowly
that it was thought to be a great distance from the sun, and comets are only normally visible in
the immediate vicinity of the sun. As its orbit came to be worked out the truth dawned that it
was a new planet far beyond Saturn’s realm, and that the ‘reviewer of the heavens’ had
stumbled across an unprecedented prize. Herschel wanted to call it georgium sidus (Star of
George) in honour of his royal patron King George III of Great Britain. The planet was later for a
time called Herschel in honour of its discoverer. The name Uranus, which was first proposed by
the German astronomer Johann Elert Bode, was in use by the late 19th century.
Uranus is a giant in construction, but not so much in size; its diameter compares unfavourably
with that of Jupiter and Saturn, though on the terrestrial scale it is still colossal. Uranus’
atmosphere consists largely of hydrogen and helium, with a trace of methane. Through a
telescope the planet appears as a small bluish-green disc with a faint green periphery. In 1977,
while recording the occultation 1 of a star behind the planet, the American astronomer James L.
Elliot discovered the presence of five rings encircling the equator of Uranus. Four more rings
were discovered in January 1986 during the exploratory flight of Voyager 2 2 , In addition to its
rings, Uranus has 15 satellites (‘moons’), the last 10 discovered by Voyager 2 on the same
flight; all revolve about its equator and move with the planet in an east—west direction. The
two largest moons, Titania and Oberon, were discovered by Herschel in 1787. The next two,
Umbriel and Ariel, were found in 1851 by the British astronomer William Lassell. Miranda,
thought before 1986 to be the innermost moon, was discovered in 1948 by the American
astronomer Gerard Peter Kuiper.
Dostları ilə paylaş: