The Submillimeter Array (SMA) is producing valuable details about the inner workings of distant clouds of molecules. It operates in the frequency range from ISO to 900 GHz (corresponding to very short wavelengths from 1.7 to 0.7 mm) where it exploits a narrow radio window in the earth's atmosphere that is partially transparent to waves at these frequencies. At other frequencies the atmosphere blocks out submillimeter waves. The array's efficacy is increased by its location on the Mauna J6i in Hawaii at an altitude of 4,080 m (13,386 ft). The SMA is a joint venture of the Smithsonian Astrophysical Observatory and the Academia Sinica Institute of Astronomy and Astrophysics in Taiwan. The Taiwanese group funded two of the dishes in the array, in return for 15% of the observing time, so that the SMA now has eight antennas, each 6 m in diameter (Figure 15.3) that can be moved to any of 24 locations spread over an area 508 in across. The maximum resolution is in the range of 0.1-0.5 arcseconds, depending on the frequency chosen. The SMA is fully productive but a summary of its key discoveries remains to be written.
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