California Institute of Technology

Chajnantor Observatory

QUIET observing at the Chajnantor Observatory

The Chajnantor Observatory, a facility operated by the California Institute of Technology (Caltech) in collaboration with the University of Chile and the University of Concepción, is located at an elevation of 5080 meters (16700 feet) in the Andes mountains in northern Chile. The high, dry Chajnantor plateau is one of the best sites in the world for millimeter and submillimeter astronomy.

The observatory is partially supported by the Strategic Alliance for the Implementation of New Technologies (SAINT).



The Q/U Imaging ExperimenT (QUIET) started making observations of the polarization of the cosmic microwave background radiation in 2008 October. A collaboration between experimental groups at Caltech, Chicago, Columbia, JPL, KEK, Manchester, MPIfR Bonn, Miami, Oslo, Oxford, Princeton, and Stanford, QUIET is a program to make very sensitive measurements of the polarization of the cosmic microwave background with large arrays of coherent correlation polarimeters. QUIET takes advantage of a breakthrough developed at JPL for the packaging of the polarimeters (“radiometer on a chip”) that allows their mass production so thousands of detectors can be used. In the first phase, two receivers have been constructed, one with 19 pixels at 44 GHz and another with 91 pixels at 90 GHz. A 1.4 m compact range antenna is attached to the CBI mount. The measurements cover angular scales from a few arc minutes to several degrees.


The Cosmic Background Imager (CBI) was a special-purpose radio telescope designed to study the early universe by measuring the intensity and polarization of fluctuations in the cosmic microwave background radiation. It consisted of 13 Cassegrain antennas on a common platform, linked as an interferometer array, and received radiation in the 26–36 GHz band. It observed the microwave background, clusters of galaxies, and selected Galactic objects from 1999 to 2008.


Anthony C. S. Readhead, Barbara and Stanley Rawn, Jr., Professor of Astronomy at Caltech.


Operations in Chile are carried out by Sociedad Astro-Norte Ingenieros Limitada.

Education and Public Outreach

The Chajnantor Observatory is carrying out an active education and outreach program with the town of San Pedro de Atacama. In this program, teachers from the San Pedro school visit the California Institute of Technology and the Jet Propulsion Laboratory in Pasadena, and they take short training courses at the Lewis Center for Educational Research in the Apple Valley. In these programs they are instructed in the use of newly-developed teachers' training tools, which they can then use in their classes in San Pedro to give their students direct access to and control of radio telescopes at Goldstone (GAVRT) and at the Owens Valley Radio Observatory. The data from these observations are used in refereed scientific papers. In addition, astronomers from the Chajnantor Observatory give lectures to the local schools and host visits of classes to the observatory.

Another important aspect of the Chajnantor Observatory is the active collaboration with undergraduates and graduate students from the Universidad de Chile and the Universidad de Concepción, and two students are currently doing PhD theses based on work carried out at the observatory.