Word: planet
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Dates: during 1990-1999
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...HARD TO IMAGINE TWO more undesirable pieces of extraterrestrial real estate. The first, a planet orbiting a star known as 47 Ursae Majoris, 200 trillion miles from Earth in the Big Dipper, is about twice the size of Jupiter. Like our own largest planet, it probably consists mostly of such noxious gases as hydrogen sulfide, ammonia and methane. Fierce jet streams blow unceasingly at hundreds of miles per hour, sometimes spiraling into mammoth hurricanes that last for centuries and are big enough to swallow the Earth. And if this harsh world has any solid surface at all, it's buried...
...realm of tangible fact. Despite years of searching with the most powerful telescopes, despite decades of listening for the faint crackle of radio signals from distant civilizations, despite endless theorizing about how life might or might not arise, nobody had ever found concrete evidence to suggest that our planet, our civilization, our life-forms were anything but unique in the cosmos...
...fascination with other worlds is as old as Western civilization. Galileo's discovery that they actually existed--that at least some of the pinpoints of light that wandered throughout the night sky had mountains and moons--set off a centuries-long quest to discover new planets. The first great success came in 1781, when William Herschel found Uranus. Then came the discovery of Neptune by Johann Galle in 1846. Eventually, the notion of otherworldly life made the transition out of the pages of philosophy and fiction: in 1894, the wealthy astronomer Percival Lowell built his own observatory in Arizona...
...that astronomers ever stopped looking--at first, within the solar system, for the mysterious Planet X (now considered very unlikely to exist), and then, as powerful instruments like the 200-in. Hale telescope came online, around other stars as well. But picking out a planet against the glare of a star is like trying to spot a 100-watt light bulb next to a 100-billion-watt searchlight. Astronomers find it much easier to look for the subtle influence a planet might have on its parent star...
...orbiting world's gravity should, for example, tug faintly on the star that is its sun, pulling it first this way, then that. If the plane of the planet's orbit is such that a star is being pulled first toward and then away from the Earth, the motion will cause light waves coming from the star to be squeezed together, then stretched apart--making the light look first a little bit bluer than it really is, then a little bit redder, then bluer again, and so on. These subtle color changes--examples of the so-called Doppler shift...