1934: Richard Tolman shows that blackbody radiation in an expanding universe cools but retains its thermal distribution and remains a blackbody.
1941: Andrew McKellar uses the excitation of CN doublet lines to measure that the "effective temperature of space" is about 2.3 K.
1948: George Gamow, Ralph Alpher, and Robert Herman predict that a Big Bang universe will have a blackbody cosmic microwave background with temperature about 5 K.
1955: Tigran Shmaonov finds excess microwave emission with a temperature of roughly 3 K. So do several other researchers, starting with Andrew McKellar's 1941 observations of the excitation of interstellar CN molecules, but they do not follow through sufficiently, until Penzias and Wilson in 1964 .
1964: A.G. Doroshkevich and Igor Novikov write an unnoticed paper suggesting microwave searches for the blackbody radiation predicted by Gamow, Alpher, and Herman.
1965: Arno Penzias and Robert Wilson discover the 3 K cosmic microwave background radiation. Through the connection of Bernie Burke, Robert Dicke, James Peebles, Roll, and Wilkinson learn of and interpret the measurement.
1966: Rainer Sachs and Arthur Wolfe theoretically predict microwave background fluctuation amplitudes created by gravitational potential variations between observers and the last scattering surface.
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 of microwave background photons by hot electrons.
1990: The COBE satellite shows that the microwave background has a nearly perfect blackbody spectrum and thereby strongly supporting the hot big bang model, the thermal history of the Universe and constrains the density of the intergalactic medium.
1992: The COBE satellite discovers anisotropy in the cosmic microwave background, this strongly supports the big bang model with gravitational instability as the source of large scale structure. This discovery energizes and motivates the field in both theory and experiment leading to an explosion of activity.
1995: The Cosmic Anisotropy Telescope performs the first high resolution observations of the cosmic microwave background.
2000: CMB anisotropy observations show that the Universe's curvature is small and that the Universe is flat for practical purposes. The CMB anisotropies begin to fulfill their promise of determining cosmological parameters first to 10% sensitivity and later more accurately.
2001: WMAP (Wilkinson Microwave Anisotropy Probe) launched as a NASA MidEX mission.
2002: Polarization discovered by DASI.
2003: The CBI and the Very Small Array produces yet higher quality maps at high resolution (covering small areas of the sky).
2009: Planck (Max Planck Surveyor formerly known as COBRAS/SAMBA) to be launched as an ESA (European Space Agency) Mission.