Word: sun
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Dates: during 1980-1989
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...agency plans to dedicate part of two shuttle missions, including the flight that will boost aloft Teacher Sharon Christa McAuliffe, to comet- related experiments. The Solar Max satellite, brought back to life l8 months ago by a shuttle repair crew and now performing its normal duty of monitoring the sun, will examine Halley's off and on for about 60 days. Pioneer 12, in orbit around Venus, will watch Halley's when it ducks behind the sun. The U.S. is also a major backer of the International Halley Watch (IHW), a vast effort to coordinate the megabytes of comet information...
...flying museum stocked with precious artifacts from the very earliest moments of the solar system. They hope that by peering into Halley's cold heart and sniffing out the dust and gases that stream from its surface, they can discern the conditions that existed at the birth of the sun and the nine planets some 4.5 billion years ago. That in turn could reveal how common an occurrence the formation of planets around other stars may be, hence how likely it is that extraterrestrial life exists. "Comets are like a cosmic refrigerator," says Paul Feldman, an astronomer at Johns Hopkins...
...Whipple, a Harvard astronomer, proffered a detailed model for the anatomy of a comet. In a delightfully evocative phrase, Whipple declared that comets are "dirty snowballs," dark conglomerates of mostly frozen water stippled with rocky fragments, dust particles and trace elements. As one of these snowballs swoops toward the sun, said Whipple, solar radiation begins to vaporize ice and frozen gases on the comet's sunward surface by a process called sublimation. The gases, carrying dust with them, form a light-reflecting coma that makes the comet visible from earth...
...would come to be known as the Oort Cloud. Basing his calculations on the shape of cometary orbits and the number of new comets observed each year, Oort postulated that the cloud surrounds the solar system in a vast region 30,000 to 100,000 astronomical units from the sun (one AU is about 93 million miles, the distance between earth and sun...
...other phenomena that have gradually changed the inner members of the solar system. Every once in a while, however, a passing star gives the cloud a gravitational jiggle, releasing hundreds of these fragments. Most of them are sent outward into interstellar space, but some are hurled toward the sun as comets. Although the Oort Cloud has yet to be seen, most astronomers agree it exists and is the flotsam left over when a nebula, a massive cloud of dust and gas, collapsed and formed the solar system...