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Astrometric interferometer successful.

Astrometric interferometer successful

In astronomy, interferometry means combining signals receivedfrom a given star at two or more different points in order to use correlations between the received signals for more accurate measurement of stellar positions and dimensions than is possible with a single telescope. The correlations can involve variations in the amplitude, intensity or phase of the signal. Interferometry, often used in radioastronomy, is only beginning to be used in optical astronomy. It was hindered in the past by technical difficulties due to the effect of atmospheric turbulence on visible light.

A pioneer phase-coherence interferometer for visible stars,Mark II, located at the Mt. Wilson observatory in Pasadena, Calif., has succesfully measured the positions of five stars to an accuracy of 3 arcseconds and tracked them over wide angles (greater than 20|) as the earth rotated. According to the astronomers involved, it shows that with improvements phase-coherence interferometry will be useful for measuring stellar positions.

The interferometer gathers light from a star at two mirrors3.1 meters apart and combines the two beams with a "beam splitter' (which here combines beams instead of splitting them) and then measures the coherence of their phases. On the way to the beam splitter one signal goes through a variable optical delay circuit intended to compensate both for the rotation of the earth during tracking and changes in atmospheric turbulence. The report is in the May ASTRONOMICAL JOURNAL by Michael Shao and M. Mark Colavita of the Smithsonian Astrophysical Observatory in Cambridge, Mass., D. H. Staelin of Massachusetts Institute of Technology, K. J. Johnston and R. S. Simon of the Naval Research Laboratory in Washington, D.C., and J. A. Hughes and J. L. Hershey of the U.S. Naval Observatory in Washington, D.C.
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Publication:Science News
Date:May 30, 1987
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