Word: planet
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Dates: during 1950-1959
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...Wallace, hybrid-corn developer and gentleman farmer, added that population trends are indeed "ruining gradually though surely the quality of human life," plumped for hereditary records and genetic guidance "to enable intelligent young people to make free-choice the matings which will increase the genetic wealth of our planet." But such instruments would never, he said hopefully, "be used by any genetic Hitler...
Deep space, far from stars or planets, is like the pond's smooth surface. An object becalmed in its emptiness floats like a galleon in the doldrums. If the object is a spaceship with propulsive power, it can cruise in any direction, meeting practically no resistance. But it must keep away from the whirlpools: the gravitational fields that surround stars and planets. If it plunges into one of them, it may end as a puff of gas in a star or a brief streak of fire in a planet's atmosphere...
Looking at it from the other end. a spaceship that starts its voyage on the surface of a planet has a hard time climbing out of its gravitational pit. Once it has reached untroubled space, it can coast for millions of miles on its unopposed momentum...
Solar Orbit. The earth and moon, whirling around each other, are not alone in space. They also orbit around the sun, and so do the other planets. A gravity chart of the solar system shows an enormously deep pit, the sun's, with much smaller pits in its slope, one for each planet. When a spaceship has climbed out of the earth's gravitational pit, it is still deep in the sun's pit. This does not mean that it will fall into the sun. Besides the comparatively small speed contributed by its own engine, it also...
...never closer than 25 million miles. To cover these great distances, it takes more time (146 days to Venus, 260 days to Mars), but only slightly more speed than is needed to go to the moon, which is only 230,000 miles away. This is because space between the planets is comparatively smooth. It is only slightly affected by planetary gravitation, and the great pull of the sun is countered by the orbital speed that a spaceship inherits from its home planet...