For millennia societies and cultures around the world interpreted the appearance of naked-eye comets in the night sky as harbingers of doom. People blamed the comets' arrivals for everything from wars and deaths to plagues and volcanic eruptions.
Krupp, who is an expert on the celestial component of belief systems, said the reason for the association of comets with trouble is a logical one: Comets disrupted the natural, rhythmic order of the sky.
"People have looked to the sky for reference to order themselves in time and space and so had a reliance on the regular, cyclical behavior of the sky, starting with the sun or moon, motions of day and night, stars coming and going," Krupp said.
Comets, which often appear with no advance warning, would disrupt this natural rhythm, making them an easy scapegoat for a war or death of a ruler that coincided within a year of so of the comet's arrival, according to Krupp.
Kronk said that the Babylonians and Chinese understood the short-period orbits of the planets and could calculate their positions as well as the timing of solar and lunar eclipses. But that the decade-, century-, or millennium-scale orbits of comets were different.
"Comets always came as a surprise," he said. "The shapes of comets did not help. There are descriptions of comets appearing like blades or swords as they moved across the sky."
Comet Understanding
Krupp said that modern understanding of comets as leftover balls of dirty ice from the formation of the sun and planets has, for most people, ended the association of comets with doom. Today, Krupp said people just want to know more about them.
"How much dirty ice? How does it form? What is the chemical composition? Does it vary from one to another? " As quoted from Krupp, such questions will be answered as exploration of the cosmos continues.
For example in January 2006 NASA's Stardust spacecraft will, for the first time, return to Earth samples of comet dust. They were collected from Comet Wild/2 in January 2004. "That becomes a concrete, specific example of what is out there," Krupp said.
According to Kronk, modern understanding of comets allows most people to appreciate them as special treats to be viewed in the night sky. But some comet hysteria continues, fueled by Internet rumors and fringe groups.
Often invited to give talks on comets, Kronk used to get audiences to laugh at a story about how people bought "comet pills" for protection in 1910. They were supposed to protect against the rumored poisonous gases within Halley's comet's tail when it passed close to Earth.
"But no one was chuckling after the Heaven's Gate group committed suicide in March of 1997 when Hale-Bopp was in the sky," Kronk said. Members of the group thought suicide was their only way to get onto a UFO rumored to be in the comet's tail.
Fortunately, added Kronk, doomsday-type events have yet to be predicted for comets Bradfield, NEAT, and LINEAR.
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