Cosmology Large Angular Scale Survey

The Cosmology Large Angular Scale Surveyor (CLASS) is an array of four microwave telescopes in Chile on Cerro Toco in the Atacama Desert at an altitude of 5200 meters, surveying CMB polarization. The telescopes are sensitive to polarization and the aim is mapping the sky's polarization modes. It aims to map CMB lensing to investigate the cosmic dawn, and to identify and study B-modes stemming from inflation.

Another use of the acronym CLASS is for Cosmic Lens All-sky Survey, a 1990s/2000s radio survey aimed at gravitational lensing.