Editing Cosmic Background Explorer (section)

=== Black-body curve of CMB ===
[[File:Cmbr.svg|thumb|upright=1.0|left|Data from COBE showed a perfect fit between the black body curve predicted by big bang theory and that observed in the microwave background. The error bars are smaller than the width of the blue curve. The red crosses merely locate the data points.]]
[[File:PIA16874-CobeWmapPlanckComparison-20130321.jpg|thumb|upright=1.0|right|Comparison of [[CMB]] results from COBE, [[Wilkinson Microwave Anisotropy Probe|WMAP]] and [[Planck (spacecraft)|Planck]] - 21 March 2013.]]

During the 15-year-long period between the proposal and launch of COBE, there were two significant astronomical developments:
* First, in 1981, two teams of astronomers, one led by David Wilkinson of [[Princeton University]] and the other by Francesco Melchiorri of the [[University of Florence]], simultaneously announced that they detected a [[quadrupole]] distribution of CMB using balloon-borne instruments. This finding would have been the detection of the black-body distribution of CMB that FIRAS on COBE was to measure. In particular, the Florence group claimed a detection of intermediate angular scale anisotropies at the level 100 [[Orders of magnitude (temperature)|microkelvins]]<ref>{{cite journal |url=http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1981ApJ...250L...1M&amp;data_type=PDF_HIGH&amp;whole_paper=YES&amp;type=PRINTER&amp;filetype=.pdf |first1=Francesco |last1=Melchiorri |first2=Bianca O. |last2=Melchiorri |last3=Pietranera |first3=Luca |title=Fluctuations in the microwave background at intermediate angular scales |journal=The Astrophysical Journal |date=November 1981 |bibcode=1981ApJ...250L...1M |access-date=2011-08-23 |doi=10.1086/183662 |last4=Melchiorri |first4=B. O. |volume=250 |page=L1}}</ref> in agreement with later measurements made by the [[BOOMERanG experiment]]. However, a number of other experiments attempted to duplicate their results and were unable to do so.<ref name=leverington/>
* Second, in 1987 a Japanese-American team led by [[Andrew E. Lange]] and Paul Richards of [[University of California, Berkeley]] and Toshio Matsumoto of [[Nagoya University]] made an announcement that CMB was not that of a true black body.<ref>{{cite journal |title=Cosmological implication of a new measurement of the submillimeter background radiation |author=Hayakawa, S. |author2=Matsumoto, T. |author3=Matsuo, H. |author4=Murakami, Hiroshi |author5=Sato, S. |author6=Lange A. E. |author7=Richards, P. |name-list-style=amp |journal=Publications of the Astronomical Society of Japan |issn=0004-6264 |volume=39 |issue=6 |date=1987 |pages=941–948 |bibcode=1987PASJ...39..941H |url=http://articles.adsabs.harvard.edu//full/1987PASJ...39..941H/0000941.000.html |access-date=17 May 2012}}</ref> In a [[sounding rocket]] experiment, they detected an excess brightness at 0.5 and {{cvt|0.7|mm}} wavelengths.

With these developments serving as a backdrop to COBE's mission, scientists eagerly awaited results from FIRAS. The results of FIRAS were startling in that they showed a perfect fit of the CMB and the theoretical curve for a black body at a temperature of 2.7 K, in contrast to the Berkeley-Nagoya results.

FIRAS measurements were made by measuring the spectral difference between a 7° patch of the sky against an internal black body. The interferometer in FIRAS covered between 2- and 95-cm−1 in two bands separated at 20-cm−1. There are two scan lengths (short and long) and two scan speeds (fast and slow) for a total of four different scan modes. The data were collected over a ten-month period.<ref name=fixsen>{{cite journal |author1=Fixsen, D. J. |author2=Cheng, E. S. |author3=Cottingham, D. A. |author4=Eplee, R. E. Jr. |author5=Isaacman, R. B. |author6=Mather, J. C. |author7=Meyer, S. S. |author8=Noerdlinger, P. D. |author9=Shafer, R. A. |author10=Weiss, R. |author11=Wright, E. L. |author12=Bennett, C. L. |author13=Boggess, N. W. |author14=Kelsall, T. |author15=Moseley, S. H. |author16=Silverberg, R. F. |author17=Smoot, G. F. |author18=Wilkinson, D. T. |date=1994 |title=Cosmic microwave background dipole spectrum measured by the COBE FIRAS instrument |bibcode=1994ApJ...420..445F |journal=Astrophysical Journal |volume=420 |issue=2 |pages=445–449 |doi=10.1086/173575}}</ref>