SEST telescope. Dish of the Swedish-ESO Sub- millimetre Telescope (SEST) at the European Southern Observatory (ESO) site at La Silla, Chile. The 15-metre diameter dish of this radio telescope is used for observations at frequencies of 70-365 gigahertz, corresponding to wavelengths of 0.8 to 42 millimetres. The parabolic surface of the dish is used to reflect & focus incoming electromagnetic radiation onto the receiving antenna above its centre.