During the past decade, a year-round observatory has been established at the geographic South Pole by the Center for Astrophysical Research in Antarctica (CARA). CARA has fielded several millimeter- and submillimeter-wave instruments: AST/RO (the Antarctic Submillimeter Telescope and Remote Observatory, a 1.7-m telescope outfitted with a variety of receivers at frequencies from 230 GHz to 810 GHz, including PoleSTAR, a heterodyne spectrometer array), Python (a degree-scale CMB telescope), Viper (a 2-m telescope which has been outfitted with SPARO, a submillimeter-wave bolometric array polarimeter, ACBAR, a multichannel CMB instrument, and Dos Equis, a HEMT polarimeter), and DASI (the Degree-Angular Scale Interferometer). These instruments have obtained significant results in studies of the interstellar medium and observational cosmology, including detections of the 1° acoustic peak in the CMB and the Sunyaev-Zel'dovich effect. The South Pole environment is unique among observatory sites for unusually low wind speeds, low absolute humidity, and the consistent clarity of the submillimeter sky. The atmosphere is dessicated by cold: at the South Pole's average annual temperature of -49°C, the partial pressure of saturated water vapor is only 1.2% of what it is at 0°C. The low water vapor levels result in exceptionally low values of sky noise. This is crucial for large-scale observations of faint cosmological sources - for such observations the South Pole is unsurpassed.
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