Word: cepheids
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Dates: during 1950-1959
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Shapley explained that astronomers have long had doubts about the yardstick they use to measure the enormous distances between the galaxies. It is based on Cepheid variable stars, whose luminosity (and therefore whose distance) can be told from their periods of pulsation. The system worked all right for a while, but recently many contradictions have shown up. For instance, the globular star clusters in the Magellanic Clouds (small, comparatively nearby galaxies) seemed to be much fainter intrinsically than similar clusters in the Milky Way. This offended the astronomers' sense of order. They felt that the clusters in both galaxies...
Instead, astronomers at Harvard and at Mt. Palomar, gathering evidence with "ordinary" telescopes and re-analyzing old data have shown that classical Cepheid variable star are actually brighter than had been assumed. Knowing the absolute or intrinsic brightness of these particular stars, and from their apparent brightness, astronomers can determine the distances of nearby galaxies. The new results show that these stars are brighter than previously suspected, so that the distances of the galaxies are about twice their older values. Thus the part of the universe that astronomers have probed has about eight times the volume they had thought...