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Holes in the Sky Provide Cosmic Measuring Rod

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Science  16 Jul 1999:
Vol. 285, Issue 5426, pp. 318-320
DOI: 10.1126/science.285.5426.318

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CHICAGO-- The shadows cast by distant galaxy clusters against the microwave glow of the sky are offering a new gauge of the universe's expansion rate and makeup. The shadows were recognized years ago, but the technique is only now showing its potential, thanks to more sensitive instruments for measuring the microwave background and satellite x-ray images of clusters. Uncertainties in the technique are still large, but results so far provide a comfortable fit with a recently announced value for the Hubble constant, the rate at which the universe is expanding.