  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 multi-channel 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 degree
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.
