Word: lightful
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Dates: during 1990-1999
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After a year, he signed on as a graduate student at Yerkes Observatory in Wisconsin and embarked on the work that would one day make him famous: studying faint, hazy blobs of light called nebulae (from the Latin word for cloud) that are visible through even a modest telescope...
...mountain, Hubble encountered his greatest scientific rival, Harlow Shapley, who had already made his reputation by measuring the size of the Milky Way. Using bright stars called Cepheid variables as standardized light sources, he had gauged the galaxy as being an astounding 300,000 light-years across--10 times as big as anyone had thought. Yet Shapley claimed that the Milky Way was the whole cosmic ball of wax. The luminous nebulae were, he insisted, just what they looked like: clouds of glowing gas that were relatively nearby...
Hubble wasn't so sure. And in 1924, three years after Shapley departed to take over the Harvard Observatory, Hubble found proof to the contrary. Spotting a Cepheid variable star in the Andromeda nebula, Hubble used Shapley's technique to show that the nebula was nearly a million light-years away, far beyond the bounds of the Milky Way. It's now known to be the full-fledged galaxy closest to our own in a universe that contains tens of billions of galaxies. "I do not know," Shapley wrote Hubble in a letter quoted by biographer Christianson, "whether...
Hubble's scientific reputation was made almost overnight by his discovery that the universe is vast and the Milky Way insignificant. But he had already moved on to a new problem. For years, astronomers had noted that light from the nebulae was redder than it should be. The most likely cause of this so-called red shifting was motion away from the observer. (The same sort of thing happens with sound: a police car's siren seems to drop in pitch abruptly as the car races past a listener...
...element after another with the newly discovered neutron. They missed by the thickness of the sheet of foil in which they wrapped their uranium sample; the foil blocked the fission fragments that their instruments would otherwise have recorded. It was a blessing in disguise. If fission had come to light in the mid-1930s, while the democracies still slept, Nazi Germany would have won a long lead toward building an atom bomb. In compensation, Fermi made the most important discovery of his life, that slowing neutrons by passing them through a light-element "moderator" such as paraffin increased their effectiveness...