The cosmic microwave background, or relic radiation, is microwave radiation that fills all space in the observable universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dark. However, a sufficiently sensitive radio telescope detects a faint background glow that is almost uniform and is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The accidental discovery of the CMB in 1965 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s.
The Wilkinson Microwave Anisotropy Probe (WMAP), originally known as the Microwave Anisotropy Probe, was a NASA spacecraft operating from 2001 to 2010 which measured temperature differences across the sky in the cosmic microwave background (CMB) – the radiant heat remaining from the Big Bang. Headed by Professor Charles L. Bennett of Johns Hopkins University, the mission was developed in a joint partnership between the NASA Goddard Space Flight Center and Princeton University. The WMAP spacecraft was launched on 30 June 2001 from Florida. The WMAP mission succeeded the COBE space mission and was the second medium-class (MIDEX) spacecraft in the NASA Explorer program. In 2003, MAP was renamed WMAP in honor of cosmologist David Todd Wilkinson (1935–2002), who had been a member of the mission's science team. After nine years of operations, WMAP was switched off in 2010, following the launch of the more advanced Planck spacecraft by European Space Agency (ESA) in 2009.
The Cosmic Background Imager was a 13-element interferometer perched at an elevation of 5,080 metres at Llano de Chajnantor Observatory in the Chilean Andes. It started operations in 1999 to study the cosmic microwave background radiation and ran until 2008.
BOOMERanG experiment was an experiment that flew a telescope on a (high-altitude) balloon and measured the cosmic microwave background radiation of a part of the sky during three sub-orbital flights. It was the first experiment to make large, high-fidelity images of the CMB temperature anisotropies, and is best known for the discovery in 2000 that the geometry of the universe is close to flat, with similar results from the competing MAXIMA experiment.
The South Pole Telescope (SPT) is a 10-metre (390 in) diameter telescope located at the Amundsen–Scott South Pole Station, Antarctica. The telescope is designed for observations in the microwave, millimeter-wave, and submillimeter-wave regions of the electromagnetic spectrum, with the particular design goal of measuring the faint, diffuse emission from the cosmic microwave background (CMB). Key results include a wide and deep survey of discovering hundreds of clusters of galaxies using the Sunyaev–Zel'dovich effect, a sensitive 5 arcminute CMB power spectrum survey, and the first detection of B-mode polarized CMB.
The Atacama Cosmology Telescope (ACT) was a cosmological millimeter-wave telescope located on Cerro Toco in the Atacama Desert in the north of Chile. ACT made high-sensitivity, arcminute resolution, microwave-wavelength surveys of the sky in order to study the cosmic microwave background radiation (CMB), the relic radiation left by the Big Bang process. Located 40 km from San Pedro de Atacama, at an altitude of 5,190 metres (17,030 ft), it was one of the highest ground-based telescopes in the world.
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 in ten bands. The instrument is similar in design to the Cosmic Background Imager (CBI) and the Very Small Array (VSA). In 2001 The DASI team announced the most detailed measurements of the temperature, or power spectrum of the cosmic microwave background (CMB). These results contained the first detection of the 2nd and 3rd acoustic peaks in the CMB, which were important evidence for inflation theory. This announcement was done in conjunction with the BOOMERanG and MAXIMA experiment. In 2002 the team reported the first detection of polarization anisotropies in the CMB.
Spider is a balloon-borne experiment designed to search for primordial gravitational waves imprinted on the cosmic microwave background (CMB). Measuring the strength of this signal puts limits on inflationary theory.
The Millimeter Anisotropy eXperiment IMaging Array (MAXIMA) experiment was a balloon-borne experiment funded by the United States NSF, NASA, and Department of Energy, and operated by an international collaboration headed by the University of California, to measure the fluctuations of the cosmic microwave background. It consisted of two flights, one in August 1998 and one in June 1999. For each flight the balloon was started at the Columbia Scientific Balloon Facility in Palestine, Texas and flew to an altitude of 40,000 metres for over 8 hours. For the first flight it took data from about 0.3 percent of the sky of the northern region near the Draco constellation. For the second flight, known as MAXIMA-II, twice the area was observed, this time in the direction of Ursa Major.
Archeops was a balloon-borne instrument dedicated to measuring the Cosmic microwave background (CMB) temperature anisotropies. The study of this radiation is essential to obtain precise information on the evolution of the Universe: density, Hubble constant, age of the Universe, etc. To achieve this goal, measurements were done with devices cooled down at 100mK temperature placed at the focus of a warm telescope. To avoid atmospheric disturbance the whole apparatus is placed on a gondola below a helium balloon that reaches 40 km altitude.
TopHat was a scientific experiment launched from McMurdo Station in January 2001 to measure the cosmic microwave background radiation produced 300,000 years after the Big Bang. The balloon was launched on January 2, 2001 and proceeded to fly for 644 hours over the continent of Antarctica before landing on January 31, 2001. The balloon flew over the continent 38 kilometers (125,000 ft) above the ground. The working payload was shut down on January 10, 2001 after the liquid cryogens cooling the detectors were exhausted, and the balloon simply circled the continent until it was safe to land. The vorticial winds that typically carry balloons around the continent dissipated part of the way through the flight, and the balloon had to be terminated in a suboptimal location. The landing missed the targeted ice shelf by around one half mile, and while the discs containing the information were recovered safely using a Twin Otter, the gondola itself had not been recovered by August 2001.
BICEP and the Keck Array are a series of cosmic microwave background (CMB) experiments. They aim to measure the polarization of the CMB; in particular, measuring the B-mode of the CMB. The experiments have had five generations of instrumentation, consisting of BICEP1, BICEP2, the Keck Array, BICEP3, and the BICEP Array. The Keck Array started observations in 2012 and BICEP3 has been fully operational since May 2016, with the BICEP Array beginning installation in 2017/18.
A balloon-borne telescope is a type of airborne telescope, a sub-orbital astronomical telescope that is suspended below one or more stratospheric balloons, allowing it to be lifted above the lower, dense part of the Earth's atmosphere. This has the advantage of improving the resolution limit of the telescope at a much lower cost than for a space telescope. It also allows observation of frequency bands that are blocked by the atmosphere.
The Cosmology Large Angular Scale Surveyor (CLASS) is an array of microwave telescopes at a high-altitude site in the Atacama Desert of Chile as part of the Parque Astronómico de Atacama. The CLASS experiment aims to improve our understanding of cosmic dawn when the first stars turned on, test the theory of cosmic inflation, and distinguish between inflationary models of the very early universe by making precise measurements of the polarization of the Cosmic Microwave Background (CMB) over 65% of the sky at multiple frequencies in the microwave region of the electromagnetic spectrum.
The Atacama B-Mode Search (ABS) was an experiment to test the theory of cosmic inflation and distinguish between inflationary models of the very early universe by making precise measurements of the polarization of the Cosmic Microwave Background (CMB). ABS was located at a high-altitude site in the Atacama Desert of Chile as part of the Parque Astronómico de Atacama. ABS began observations in February 2012 and completed observations in October 2014.
The Simons Observatory is located in the high Atacama Desert in Northern Chile inside the Chajnator Science Preserve, at an altitude of 5,200 meters (17,000 ft). The Atacama Cosmology Telescope (ACT) and the Simons Array are located nearby and these experiments are currently making observations of the Cosmic Microwave Background (CMB). Their goals are to study how the universe began, what it is made of, and how it evolved to its current state. The Simons Observatory shares many of the same goals but aims to take advantage of advances in technology to make far more precise and diverse measurements. In addition, it is envisaged that many aspects of the Simons Observatory will be pathfinders for the future CMB-S4 array.
The QUIJOTE CMB Experiment is an ongoing experiment started in November 2012, and led by Rafael Rebolo López, with the goal of characterizing the polarization of the cosmic microwave background (CMB) and other galactic and extragalactic emission in the frequency range 10 to 40 GHz, at angular scales of 1°. These measurements will complement at low frequency and correct from galactic contamination those obtained by the Planck satellite from 2009 to 2013.
Michele Limon is an Italian research scientist at the University of Pennsylvania. Limon studied physics at the Università degli Studi di Milano in Milan, Italy and completed his post-doctoral work at the University of California, Berkeley. He has been conducting research for more than 30 years and has experience in the design of ground, balloon and space-based instrumentation. His academic specialties include Astrophysics, Cosmology, Instrumentation Development, and Cryogenics.
LiteBIRD is a planned small space observatory that aims to detect the footprint of the primordial gravitational wave on the cosmic microwave background (CMB) in a form of polarization pattern called B-mode.
