The search for planets beyond Neptune began following the discovery of
the planet Neptune in 1846, amid considerable speculation that another
planet might exist beyond its orbit. The search began in the mid-19th
century but culminated at the start of the 20th with Percival Lowell's
quest for Planet X. Lowell proposed the Planet X hypothesis to explain
apparent discrepancies in the orbits of the gas giants, particularly
Uranus and Neptune, speculating that the gravity of a large unseen
ninth planet could have perturbed Uranus enough to account for the
irregularities. Clyde Tombaugh's discovery of Pluto in 1930 appeared to
validate Lowell's hypothesis, and Pluto was officially considered the
ninth planet until 2006. In 1978, Pluto was found to be too small for
its gravity to affect the gas giants, resulting in a brief search for a
tenth planet. The search was largely abandoned in the early 1990s, when
a study of measurements made by the Voyager 2 spacecraft found that the
irregularities observed in Uranus's orbit were due to a slight
overestimation of Neptune's mass.
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Today's selected anniversaries:
SN 1006 , the brightest supernova in recorded history, first appeared
in the constellation Lupus, and was then seen by observers in
Switzerland, Egypt, China, Japan, and possibly North America within the
Arauco War: Spanish forces of the Governor Francisco de Villagra
launched a dawn surprise attack against the Mapuche headed by their
toqui Lautaro in what is now Chile.
A crowd of workers unemployed due to the Panic of 1893 conducted the
first significant popular protest march on Washington, D.C.
Second World War: The Royal Navy submarine HMS Seraph deposited the
body of a supposed British military intelligence officer with false
documents off the coast of Spain to deceive Germany about the upcoming
invasion of Sicily.
North Vietnamese troops captured Saigon shortly after American forces
ended its helicopter evacuation of U.S. citizens, South Vietnamese
civilians and third country nationals from the city, ending the Vietnam
War with the unconditional surrender of South Vietnam.
Wiktionary's word of the day:
Characterized by harmony or agreement
Wikiquote quote of the day:
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