The Cosmic Background Imager (or CBI) was a 13-element

interferometer Interferometry is a technique which uses the ''interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber op ...

perched at an elevation of 5,080 metres (16,700 feet) at

Llano de Chajnantor Observatory Llano de Chajnantor Observatory is the name for a group of astronomical observatories located at an altitude of over 4,800 m (15,700 ft) in the Atacama Desert of northern Chile. The site is in the Antofagasta Region approximately 50 kil ...

in the

Chile Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...

Andes The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...

. It started operations in 1999 to study the

cosmic microwave background radiation In Big Bang cosmology the cosmic microwave background (CMB, CMBR) is electromagnetic radiation that is a remnant from an early stage of the universe, also known as "relic radiation". The CMB is faint cosmic background radiation filling all spac ...

and ran until 2008. CBI conducted measurements at frequencies between 26 and 36

GHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that one he ...

in ten bands of 1 GHz

bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...

. It had a resolution of better than 1/10 of a degree. (In comparison, the pioneering COBE satellite, which produced the first detection of fluctuations in the microwave background in 1992, had a resolution of about 7 degrees.) Among the key findings of the CBI is the fact that fluctuations which have a small size on the sky are weaker than fluctuations which have a large size on the sky, which confirmed earlier theoretical predictions. More technically, CBI was the first experiment to detect intrinsic anisotropy in the

microwave Microwave is a form of electromagnetic radiation with wavelengths ranging from about one meter to one millimeter corresponding to frequencies between 300 MHz and 300 GHz respectively. Different sources define different frequency ran ...

background on mass scales of galaxy clusters; it provided the first detection of the Silk damping tail; it found a hint of excess power at high-l multipoles (CBI-excess) than expected from the

ΛCDM The ΛCDM (Lambda cold dark matter) or Lambda-CDM model is a parameterization of the Big Bang cosmological model in which the universe contains three major components: first, a cosmological constant denoted by Lambda (Greek Λ) associated with d ...

model; and it detected fluctuations in the polarization of the microwave background obtaining the first detailed E-mode polarization spectrum providing evidence that it is out of phase with the total intensity mode spectrum. The CBI was built at the

California Institute of Technology The California Institute of Technology (branded as Caltech or CIT)The university itself only spells its short form as "Caltech"; the institution considers other spellings such a"Cal Tech" and "CalTech" incorrect. The institute is also occasional ...

, and employed sensitive radio amplifiers from the

National Radio Astronomy Observatory The National Radio Astronomy Observatory (NRAO) is a federally funded research and development center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc. for the purpose of radio a ...

; two similar experiments are the

Very Small Array The Very Small Array (VSA) was a 14-element interferometric radio telescope operating between 26 and 36 GHz that is used to study the cosmic microwave background radiation. It was a collaboration between the University of Cambridge, Univers ...

, operated on the island of

Tenerife Tenerife (; ; formerly spelled ''Teneriffe'') is the largest and most populous island of the Canary Islands. It is home to 43% of the total population of the archipelago. With a land area of and a population of 978,100 inhabitants as of Janu ...

, and the

Degree Angular Scale Interferometer The Degree Angular Scale Interferometer (DASI) was a telescope installed at the U.S. National Science Foundation's Amundsen–Scott South Pole Station in Antarctica. It was a 13-element interferometer operating between 26 and 36 GHz (Ka band ...

, operated in

Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...

. Both of these experiments used radio interferometry to measure CMB fluctuations at lower resolution over larger areas of the sky. Another experiment operated from Antarctica, the

Arcminute Cosmology Bolometer Array Receiver ACBAR was an experiment to measure the anisotropy of the Cosmic microwave background. It was active 2000-2008. The ACBAR 145 GHz measurements were the most precise high multipole measurements of the CMB at the time. See also *Cosmic microwa ...

, used total power (bolometric) detection and a single antenna at higher frequency and similar

angular resolution Angular resolution describes the ability of any image-forming device such as an optical or radio telescope, a microscope, a camera, or an eye, to distinguish small details of an object, thereby making it a major determinant of image resolution. ...

to obtain results comparable to the CBI. The confluence of these and other CMB experiments employing different measurement techniques in recent years is a great triumph of observational cosmology. CBI was a collaboration among a number of institutions in the US and Europe. It still closely collaborates with Chilean institutions

Universidad de Chile The University of Chile ( es, Universidad de Chile) is a public research university in Santiago, Chile. It was founded on November 19, 1842, and inaugurated on September 17, 1843.

and

Universidad de Concepción Universidad (Spanish for "university") may refer to: Places * Universidad, San Juan, Puerto Rico * Universidad (Madrid) Football clubs * Universidad SC, a Guatemalan football club that represents the Universidad de San Carlos de Guatemala ...

through the Chajnantor Observatory. In 2006, new 1.4 m antennas replaced the old 0.9 m dishes for more high-resolution studies in total intensity mode. During this stage, CBI was called CBI-2. In June 2008, CBI-2 stopped the observations and the 13-antenna instrument was removed from its mount. The new

QUIET telescope Quiet may refer to: * Silence, a relative or total lack of sound In music * The Quiett (born 1985), South Korean rapper * ''Quiet'' (album), a 1996 John Scofield album * "Quiet", a song by Lights, from her album '' The Listening'' (2009) * "Qui ...

instrument was installed in August 2008 on the CBI mount, replacing CBI-2 .

External links

Caltech Chajnantor Observatory

Official Web Page
{{Portal bar, Chile, Astronomy, Stars, Spaceflight, Outer space, Solar System Radio telescopes Astronomical observatories in Chile Interferometric telescopes Buildings and structures in Antofagasta Region Cosmic microwave background experiments Science and technology in Chile