Word: cepheids
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Dates: during 1990-1999
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...researchers relied on Cepheid variable stars, whose brightness is constant and measured, as an indicator of distance of the remote galaxies...
...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...
...observations were moved to the head of the Hubble schedule, and by July, Freedman was looking at a pattern on her computer screen that was as familiar as the face of an old friend. "Boom!" she remembers. "All of a sudden there was this glorious Cepheid light curve, as beautiful as any that have ever been measured." By the end of the observing run, Freedman and her colleagues found 19 more, enough to peg M100's distance at some 56 million light-years from Earth...
...know the rate of expansion. Formally known as the Hubble constant, this expansion factor is calculated by measuring the distance from our galaxy to other galaxies (something difficult to do) and determining how fast that distance is increasing (an easier task). Scientists look for particular kinds of stars, called Cepheid variables, because they know the inherent brightness of these stars. The fainter they appear here on earth, the farther away they are, and the distance can be roughly calculated. As researchers find Cepheids farther and farther away, calculations of the Hubble constant become more and more accurate...