Astronomers using two instruments on the Hubble Space Telescope have refined the value for the Hubble Constant to within an error margin of less than 5%, pointing the way to a better understanding of the force astrophysicists call "dark energy." A team headed by Adam Riess of the Space Telescope Science Institute and the Johns Hopkins University used the orbiting observatory's Near Infrared Camera and Multi-Object Spectrometer and its Advanced Camera for Surveys (ACS) to make extremely precise measurements across vast distances, giving a much more exact value for the rate of expansion of the Universe. Basically, the team started with NGC 4258, a nearby galaxy at a distance that has been measured very precisely with radio telescopes.
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