South Pole Telescope - The Telescope

The Telescope

The telescope is a 10 meter (394 in) off-axis Gregorian telescope in an altazimuth mount (at the poles, an altazimuth mount is effectively identical to an equatorial mount). It was designed to allow a large field of view (about 1 square degree) while minimizing systematic uncertainties from ground spill-over and scattering off the telescope optics. The surface of the telescope mirror is smooth down to roughly 25 micrometers (one thousandth of an inch), which allows sub-millimeter wavelength observations. The secondary mirror is cooled to 10 K, and metal mesh filters block excess high frequency radiation to keep the thermal loading on the camera down. A key advantage of the SPT observing strategy is that the entire telescope is scanned, so the beam does not move relative to the telescope mirrors. The fast scanning of the telescope and its large field of view makes SPT efficient at surveying large areas of sky, which is required to achieve the science goals of the SPT cluster survey and CMB polarization measurements.