Halley's Comet is the best-known of the short-period comets, and is
visible from Earth every 75 to 76 years. Halley is the only
short-period comet that is clearly visible to the naked eye, and thus,
the only naked-eye comet that might appear twice in a human lifetime.
Other naked-eye comets may be brighter and more spectacular, but will
appear only once in thousands of years. Halley's returns to the inner
solar system have been observed by astronomers since at least 240 BC,
and recorded by Chinese, Babylonian, and mediaeval European
chroniclers, but were not recognised as reappearances of the same
object. The comet's periodicity was first determined in 1705 by English
astronomer Edmond Halley, after whom it is now named. It last appeared
in the inner Solar System in 1986 and will next appear in mid-2061.
During its 1986 apparition, Halley's Comet became the first to be
observed in detail by spacecraft, providing the first observational
data on the structure of the comet nucleus and the mechanism of coma
and tail formation. These observations supported a number of
longstanding hypotheses about comet construction, particularly Fred
Whipple's "dirty snowball" model, which correctly surmised that Halley
would be composed of a mixture of volatile ices, such as water, carbon
dioxide and ammonia, and dust. However, the missions also provided data
which substantially reformed and reconfigured these ideas; for instance
it is now understood that Halley's surface is largely composed of
dusty, non-volatile materials, and that only a small portion of it is
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Today's selected anniversaries:
War of the Austrian Succession: British ships began attacking the
Spanish rear of a Franco-Spanish combined fleet in the Mediterranean
Sea off the coast near Toulon, France.
Under the terms of the Adams–Onís Treaty, Spain sold Florida and other
North American territory to the United States for about US$5 million.
Members of the White Rose, a nonviolent resistance movement in Nazi
Germany that became known for a leaflet campaign that called for active
opposition to Adolf Hitler's regime, were found guilty of treason and
Lee Petty won the first Daytona 500 NASCAR auto race at the Daytona
International Speedway in Daytona Beach, Florida, US.
Jonas Savimbi, leader of the Angolan anti-Communist rebel and political
party UNITA, was killed in a battle with Angolan government troops.
Wiktionary's word of the day:
1. A reinforced eyelet, or a small metal or plastic ring used to
reinforce an eyelet.
2. (sports) A young or inexperienced surfer, skateboarder or
Wikiquote quote of the day:
The Citizens of the United States of America have a right to applaud
themselves for giving to Mankind examples of an enlarged and liberal
policy: a policy worthy of imitation. All possess alike liberty of
conscience and immunities of citizenship. It is now no more that
toleration is spoken of, as if it was by the indulgence of one class of
people that another enjoyed the exercise of their inherent natural
rights. For happily the Government of the United States, which gives to
bigotry no sanction, to persecution no assistance, requires only that
they who live under its protection should demean themselves as good
citizens in giving it on all occasions their effectual support.
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