Timeline of cosmic microwave background astronomy

Thermal temperature predictions

• 1896 - Charles Edouard Guillaume
  Charles Edouard Guillaume
  Charles Édouard Guillaume was a Swiss physicist who received the Nobel Prize in Physics in 1920 in recognition of the service he had rendered to precision measurements in physics by his discovery of anomalies in nickel steel alloys.Guillaume is known for his discovery of nickel-steel alloys he...
  
   estimates the "radiation of the stars" to be 5.6K
  Kelvin
  The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
  
  .
• 1926 - Sir Arthur Eddington estimates the non-thermal radiation of starlight in the galaxy ".. by the formula E = σT⁴ the effective temperature corresponding to this density is 3.18º absolute .. black body"
• 1930s - Cosmologist Erich Regener
  Erich Regener
  Erich Rudolf Alexander Regener was a German physicist known primarily for the design and construction of instruments to measure cosmic ray intensity at various altitudes....
  
   calculates that the non-thermal spectrum of cosmic rays in the galaxy has an effective temperature of 2.8K
• 1931 - Term microwave first used in print: "When trials with wavelengths as low as 18 cm. were made known, there was undisguised surprise+that the problem of the micro-wave had been solved so soon." Telegraph & Telephone Journal XVII. 179/1
• 1934 - Richard Tolman shows that black-body radiation in an expanding universe cools but remains thermal
• 1938 - Nobel Prize winner (1920) Walther Nernst
  Walther Nernst
  Walther Hermann Nernst FRS was a German physical chemist and physicist who is known for his theories behind the calculation of chemical affinity as embodied in the third law of thermodynamics, for which he won the 1920 Nobel Prize in chemistry...
  
   reestimates the cosmic ray temperature as 0.75K
• 1941 - Andrew McKellar
  Andrew McKellar
  Dr. Andrew McKellar was a Canadian astronomer.He was born in Vancouver, British Columbia, Canada, to Scottish parents, one of six children of John H. and Mary Littleson McKellar. He studied mathematics and physics at the University of British Columbia, graduating in 1930...
  
   uses the excitation of CN doublet lines to measure that the "effective temperature of space" is about 2.3 K
  Kelvin
  The kelvin is a unit of measurement for temperature. It is one of the seven base units in the International System of Units and is assigned the unit symbol K. The Kelvin scale is an absolute, thermodynamic temperature scale using as its null point absolute zero, the temperature at which all...
  
  
• 1946 - Robert Dicke predicts ".. radiation from cosmic matter" at <20 K, but did not refer to background radiation
• 1946 - George Gamow
  George Gamow
  George Gamow , born Georgiy Antonovich Gamov , was a Russian-born theoretical physicist and cosmologist. He discovered alpha decay via quantum tunneling and worked on radioactive decay of the atomic nucleus, star formation, stellar nucleosynthesis, Big Bang nucleosynthesis, cosmic microwave...
  
   calculates a temperature of 50 K (assuming a 3-billion year old Universe), commenting it ".. is in reasonable agreement with the actual temperature of interstellar space", but does not mention background radiation.
• 1953 - Erwin Finlay-Freundlich
  Erwin Finlay-Freundlich
  Erwin Finlay-Freundlich was a German astronomer, a pupil of Felix Klein. He was born in Biebrich, Germany. Freundlich was a working associate of Albert Einstein and introduced experiments for which the general theory of relativity could be tested by astronomical observations based on the...
  
   in support of his tired light
  Tired light
  Tired light is a class of hypothetical redshift mechanisms that was proposed as an alternative explanation for the redshift-distance relationship. These models have been proposed as alternatives to the metric expansion of space of which the Big Bang and the Steady State cosmologies are the most...
  
   theory, derives a blackbody temperature for intergalactic space of 2.3K with comment from Max Born
  Max Born
  Max Born was a German-born physicist and mathematician who was instrumental in the development of quantum mechanics. He also made contributions to solid-state physics and optics and supervised the work of a number of notable physicists in the 1920s and 30s...
  
   suggesting radio astronomy as the arbitrator between expanding and infinite cosmologies.

Microwave background radiation predictions

• 1946 - George Gamow
  George Gamow
  George Gamow , born Georgiy Antonovich Gamov , was a Russian-born theoretical physicist and cosmologist. He discovered alpha decay via quantum tunneling and worked on radioactive decay of the atomic nucleus, star formation, stellar nucleosynthesis, Big Bang nucleosynthesis, cosmic microwave...
  
   calculates a temperature of 50 K (assuming a 3-billion year old Universe), commenting it ".. is in reasonable agreement with the actual temperature of interstellar space", but does not mention background radiation.
• 1948 - Ralph Alpher and Robert Herman
  Robert Herman
  Robert Herman was a United States scientist, best known for his work with Ralph Alpher in 1948-50, on estimating the temperature of cosmic microwave background radiation from the Big Bang explosion....
  
   estimate "the temperature in the Universe" at 5 K. Although they do not specifically mention microwave background radiation, it may be inferred.
• 1949 - Ralph Alpher and Robert Herman re-re-estimate the temperature at 28 K.
• 1957 - Tigran Shmaonov reports that "the absolute effective temperature of the radioemission background ... is 4+/- 3K". It is noted that the "measurements showed that radiation intensity was independent of either time or direction of observation .. it is now clear that Shmaonov did observe the cosmic microwave background at a wavelength of 3.2cm"
• 1960s - Robert Dicke re-estimates a microwave background radiation temperature of 40K
• 1964 - A. G. Doroshkevich
  A. G. Doroshkevich
  A. G. Doroshkevich is a Russian theoretical astrophysicist and cosmologist.He is best known for his work with Igor Novikov on the recognition of Cosmic microwave background radiation as a detectable phenomenon in the spring of 1964....
  
   and Igor Dmitrievich Novikov write an unnoticed paper suggesting microwave searches for the black-body radiation predicted by Gamow, Alpher, and Herman.
• 1965 - Arno Penzias, Robert Wilson
  Robert Woodrow Wilson
  For the American President, see Woodrow Wilson.Robert Woodrow Wilson is an American astronomer, 1978 Nobel laureate in physics, who with Arno Allan Penzias discovered in 1964 the cosmic microwave background radiation...
  
  , Bernie Burke, Robert Dicke, and James Peebles discover the cosmic microwave background radiation, eventually confirmed at approximately 2.7K
• 1966 - Rainer Sachs and Arthur Michael Wolfe
  Arthur Michael Wolfe
  Arthur Michael Wolfe is an American astrophysicist, professor and the former Director of the Center for Astrophysics & Space Sciences at the University of California, San Diego. Together with Rainer Kurt Sachs, he authored the Sachs-Wolfe effect.-External links:*...
  
   theoretically predict microwave background fluctuation amplitudes created by gravitational potential variations between observers and the last scattering surface (see Sachs-Wolfe effect
  Sachs-Wolfe effect
  The Sachs–Wolfe effect, named after Rainer Kurt Sachs and Arthur Michael Wolfe, is a property of the cosmic microwave background radiation , in which photons from the CMB are gravitationally redshifted, causing the CMB spectrum to appear uneven...
  
  )
• 1968 - Martin Rees and Dennis Sciama theoretically predict microwave background fluctuation amplitudes created by photons traversing time-dependent potential wells
• 1969 - R. A. Sunyaev and Yakov Zel'dovich study the inverse Compton scattering
  Compton scattering
  In physics, Compton scattering is a type of scattering that X-rays and gamma rays undergo in matter. The inelastic scattering of photons in matter results in a decrease in energy of an X-ray or gamma ray photon, called the Compton effect...
  
   of microwave background photons by hot electrons (see Sunyaev-Zel'dovich effect
  Sunyaev-Zel'dovich effect
  The Sunyaev–Zel'dovich effect is the result of high energy electrons distorting the cosmic microwave background radiation through inverse Compton scattering, in which the low energy CMB photons receive energy boost during collision with the high energy cluster electrons...
  
  )
• 1983 - Researchers from the Cambridge Radio Astronomy Group
  Cavendish Astrophysics Group
  The Cavendish Astrophysics Group is based at the Cavendish Laboratory at the University of Cambridge. The group operates all of the telescopes at the Mullard Radio Astronomy Observatory except for the 32m MERLIN telescope, which is operated by Jodrell Bank.The group is the second largest of three...
  
   and the Owens Valley Radio Observatory
  Owens Valley Radio Observatory
  The Owens Valley Radio Observatory is a radio observatory located near Bishop, California, within the Owens Valley, California region, approximately 250 miles north of Los Angeles on the east side of the Sierra Nevada. It is owned and operated by the California Institute of Technology. For...
  
   first detect the Sunyaev-Zel'dovich effect
  Sunyaev-Zel'dovich effect
  The Sunyaev–Zel'dovich effect is the result of high energy electrons distorting the cosmic microwave background radiation through inverse Compton scattering, in which the low energy CMB photons receive energy boost during collision with the high energy cluster electrons...
  
   from clusters of galaxies
  Galaxy cluster
  A galaxy cluster is a compact cluster of galaxies. Basic difference between a galaxy group and a galaxy cluster is that there are many more galaxies in a cluster than in a group. Also, galaxies in a cluster are more compact and have higher velocity dispersion. One of the key features of cluster is...
  
  
• 1990 - The Cosmic Background Explorer (COBE
  COBE
  The COsmic Background Explorer , also referred to as Explorer 66, was a satellite dedicated to cosmology. Its goals were to investigate the cosmic microwave background radiation of the universe and provide measurements that would help shape our understanding of the cosmos.This work provided...
  
  ) satellite shows that the microwave background has a nearly perfect black-body spectrum and thereby strongly constrains the density of the intergalactic medium.
• January 1992 - Scientists that analysed data from the RELIKT-1
  RELIKT-1
  RELIKT-1 - a Soviet cosmic microwave background anisotropy experiment on board the Prognoz 9 satellite gave upper limits on the large-scale anisotropy. A reanalysis of the data in the later years claimed a confident blackbody form and anisotropy of the cosmic microwave background radiation...
  
   report the discovery of anisotropy
  Anisotropy
  Anisotropy is the property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties An example of anisotropy is the light...
  
   in the cosmic microwave background at the Moscow astrophysical seminar.
• 1992 - Scientists that analysed data from COBE
  COBE
  The COsmic Background Explorer , also referred to as Explorer 66, was a satellite dedicated to cosmology. Its goals were to investigate the cosmic microwave background radiation of the universe and provide measurements that would help shape our understanding of the cosmos.This work provided...
  
   report the discovery of anisotropy
  Anisotropy
  Anisotropy is the property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties An example of anisotropy is the light...
  
   in the cosmic microwave background.
• 1995 - The Cosmic Anisotropy Telescope
  Cosmic Anisotropy Telescope
  The Cosmic Anisotropy Telescope CAT was a three-element interferometer for cosmic microwave background radiation observations at 13 to 17 GHz, based at the Mullard Radio Astronomy Observatory. In 1995, it was the first instrument to measure small-scale structure in the cosmic microwave background...
  
   performs the first high resolution observations of the cosmic microwave background.
• 1999 - The BOOMERanG experiment
  BOOMERanG experiment
  The BOOMERanG experiment measured the cosmic microwave background radiation of a part of the sky during three sub-orbital balloon flights. It was the first experiment to make large, high fidelity images of the CMB temperature anisotropies...
  
   makes higher quality maps at intermediate resolution, and confirms that the Universe is "flat".
• 2003 - The CBI
  Cosmic Background Imager
  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...
  
   and the Very Small Array
  Very Small Array
  The Very Small Array is a 14-element interferometric radio telescope operating between 26 and 36 GHz that is used to study the cosmic microwave background radiation. It is a collaboration between the University of Cambridge, University of Manchester and the Instituto de Astrofisica de Canarias...
  
   produces yet higher quality maps at high resolution (covering small areas of the sky).
• 2003 - The WMAP spacecraft produces an even higher quality map at low and intermediate resolution of the whole sky (WMAP provides no high-resolution data, but improves on the intermediate resolution maps from BOOMERanG
  BOOMERanG experiment
  The BOOMERanG experiment measured the cosmic microwave background radiation of a part of the sky during three sub-orbital balloon flights. It was the first experiment to make large, high fidelity images of the CMB temperature anisotropies...
  
  ).
• 2004 - E-mode polarization spectrum obtained by the CBI
  Cosmic Background Imager
  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...
  
  .
• 2004 - The Arcminute Cosmology Bolometer Array Receiver
  Arcminute Cosmology Bolometer Array Receiver
  ACBAR is an experiment to measure the anisotropy of the Cosmic microwave background.The ACBAR 145 GHz measurements are the most precise high multipole measurements of the CMB to date.-External links:**...
  
   produces a higher quality map of the high resolution structure not mapped by WMAP.
• 2005 - The Arcminute Microkelvin Imager
  Arcminute Microkelvin Imager
  The Arcminute Microkelvin Imager consists of a pair of interferometric radio telescopes - the Small and Large Arrays - located at the Mullard Radio Astronomy Observatory near Cambridge. AMI was designed, built and is operated by the Cavendish Astrophysics Group...
  
   and the Sunyaev-Zel'dovich Array
  Sunyaev-Zel'dovich Array
  The Sunyaev–Zel'dovich Array in California is an array of eight 3.5 meter telescopes that is now operating as part of the Combined Array for Research in Millimeter-wave Astronomy . Its initial goals were to survey the Cosmic Microwave Background in order to measure its fine-scale anisotropies...
  
   begin the first surveys for very high redshift clusters of galaxies
  Galaxy cluster
  A galaxy cluster is a compact cluster of galaxies. Basic difference between a galaxy group and a galaxy cluster is that there are many more galaxies in a cluster than in a group. Also, galaxies in a cluster are more compact and have higher velocity dispersion. One of the key features of cluster is...
  
   using the Sunyaev-Zel'dovich effect
  Sunyaev-Zel'dovich effect
  The Sunyaev–Zel'dovich effect is the result of high energy electrons distorting the cosmic microwave background radiation through inverse Compton scattering, in which the low energy CMB photons receive energy boost during collision with the high energy cluster electrons...
  
  .
• 2009 - The Planck spacecraft will give improved precision at all resolutions (in 2012)