Word: sun
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Dates: during 1970-1979
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Wispy Hydrogen. Tugged by the gravity of a passing star, chunks of the Oort debris are occasionally pulled into orbits closer to the sun. Then perturbed further by the gravity of a massive planet, probably Saturn or Jupiter, they often enter a highly elliptical orbit that swings them close to the sun and then so far out again that they do not return to the vicinity of the sun for years. Some, like Encke's comet, which makes a pass around the sun every 3.3 years, have relatively small orbits. Others loop out billions of miles from the sun...
...comet enters the inner part of the solar system, the sun's heat begins to liberate dust and gases from the nucleus, forming a large cloud called the coma. Such clouds may become Jovian in proportions, with a diameter of more than 100,000 miles, though they are very thinly dispersed. In 1969 and 1970, NASA'S Orbiting Astronomical Observatory (OAO-2) discovered that the coma of comets is surrounded by a still larger ball of wispy hydrogen that may far exceed the sun's diameter of 860,000 miles...
...hydrogen cloud is believed to be formed from the dissociation of water molecules in the nucleus. As the comet nears the sun, it acquires its most characteristic feature. Bombarded steadily by the charged particles of the solar wind and by the slight but measurable pressure of sunlight itself, the cometary gases and dust are swept back to form one or more glowing tails. These may reach lengths of 60 million miles or more, roughly two-thirds the distance between earth and sun. Regardless of the direction of the comet's travels, its tail is always directed away from...
...century, DeCheseaux's comet sprouted seven distinct tails that fanned out peacock-like. Some comets do not develop tails at all. As of last week, however, Kohoutek was developing a classic appendage, which should continue to increase in length and grandeur until the comet comes close to the sun. Most comets survive this relatively close flyby of the sun and emerge, sometimes altered in appearance, with even more brilliant tails. Others, affected by the sun's powerful gravity, have broken up and vanished, as did the debris of Biela's comet after it split...
...that Kohoutek's nucleus is about 25 miles in diameter, far larger than most comets, probably including Halley's. Other astronomers calculate that Kohoutek weighs about 1 trillion tons. But size is not Kohoutek's only distinction. It will pass within 13 million miles of the sun. That close flyby, well within the orbit of Mercury, should make for a dazzling interaction between sun and comet. Perhaps most important of all, astronomers describe it as a "dirty" comet, one with an outer layer of dust that has probably never been stripped off by solar heating. That layer...