Edmond Halley and His Comet
Until the last few hundred years, the sudden appearance of a bright comet was interpreted as a sign of danger, war, or famine. Such was the case in the year 1066, when a comet now known as Halley's Comet appeared before the Battle of Hastings (which led to the Norman Conquest of England); its appearance was deemed significant enough to be depicted in the Bayeux Tapestry. Comets were thought to be atmospheric phenomena until Danish astronomer Tycho Brahe demonstrated that the great comet of 1577 was appreciably more distant than the moon.
A century later Isaac Newton was asked by his fellow Royal Society members, physicist Robert Hooke and astronomer Edmond Halley, to look into the problem of planetary motion with which they were struggling unsuccessfully. Newton showed (and later described in Principia) that his laws of motion and gravitation applied to comets as well as planets and other objects in the solar system. Filled with "joy and amazement" (in his own words), Halley then calculated the orbital elements of 24 observed comets and discerned that those seen in 1531, 1607, and 1682 had similar, highly eccentric orbits and thus were likely one and the same comet. He predicted that the comet would reappear after about 76 years.
Comets have been a constant source of fascination for scientists. Some astronomers, such as Charles Messier, have discovered numerous comets, and Maria Mitchell, the first female U.S. astronomer, initially achieved fame by her discovery of a comet in 1847. The composition of comets was better understood after Fred Whipple in 1959 proposed his "dirty snowball" model. In the 1970s physicist Luis Alvarez suggested that the collision of a meteor, possibly a comet fragment, with the earth may have caused the extinction of the dinosaurs at the end of the Cretaceous Period. Although controversial, this fascinating theory became widely popular.
As for Halley's Comet, it returned to perihelion in 1759, just as he had predicted, convincing the last skeptics of the power of Newtonian mechanics. The comet then returned in 1835, 1910, and 1986--every 76 years--bridging gaps between generations of scientists who keep looking at the sky and keep wondering.
A century later Isaac Newton was asked by his fellow Royal Society members, physicist Robert Hooke and astronomer Edmond Halley, to look into the problem of planetary motion with which they were struggling unsuccessfully. Newton showed (and later described in Principia) that his laws of motion and gravitation applied to comets as well as planets and other objects in the solar system. Filled with "joy and amazement" (in his own words), Halley then calculated the orbital elements of 24 observed comets and discerned that those seen in 1531, 1607, and 1682 had similar, highly eccentric orbits and thus were likely one and the same comet. He predicted that the comet would reappear after about 76 years.
Comets have been a constant source of fascination for scientists. Some astronomers, such as Charles Messier, have discovered numerous comets, and Maria Mitchell, the first female U.S. astronomer, initially achieved fame by her discovery of a comet in 1847. The composition of comets was better understood after Fred Whipple in 1959 proposed his "dirty snowball" model. In the 1970s physicist Luis Alvarez suggested that the collision of a meteor, possibly a comet fragment, with the earth may have caused the extinction of the dinosaurs at the end of the Cretaceous Period. Although controversial, this fascinating theory became widely popular.
As for Halley's Comet, it returned to perihelion in 1759, just as he had predicted, convincing the last skeptics of the power of Newtonian mechanics. The comet then returned in 1835, 1910, and 1986--every 76 years--bridging gaps between generations of scientists who keep looking at the sky and keep wondering.
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