The cosmic microwave background is a window on the early universe that is rich in information on the origin of structure in the universe and the values of the fundamental cosmic parameters. Observational cosmology as a precision science dates only from 1992, when the Cosmic Background Explorer (COBE) detected fluctuations in the background. George Smoot and John Mather shared the 2006 Nobel Prize for this work. Although the fluctuations in the temperature of the background amount to only 1 part in 105, they nevertheless have imprinted within them information on the distribution of matter in the early universe.

The most-cited papers in the past decade are based on results from the Wilkinson Microwave Anisotropy Probe (WMAP), the successor to COBE. WMAP provided data of sufficient accuracy to discriminate between cosmological models. This group of papers gives a value of 13.7 billion years for the age of the universe, and establishes that the geometry is flat. The matter content of the universe is given as 4.4% baryons (i.e., visible matter such as stars and galaxies), 22% dark matter, and 73% dark energy. One paper draws attention to evidence that the expansion of the universe is accelerating, thus reviving Einstein’s concept of a cosmological constant, a speculation that had been dismissed for decades.

The accelerating universe is the focus of attention for several of the most-cited papers in the past two years. Three of the most-cited papers showcase evidence for acceleration from the new sub-discipline, supernova cosmology. One paper combines results from the Sloan Digital Sky Survey and WMAP to refine even further the values of the cosmological parameters. Papers in this two-year group chart the emergence of a "consensus cosmology" in which the values of the parameters are no longer a matter for debate because they are now so tightly constrained. Other topics touched on are neutrino mass (which is extremely small and could be zero), the linear growth of structure in the universe from a redshift of 1000 to the present, and the results from galaxy redshift surveys.

Methodology

To construct this database, papers were extracted based on topic-supplied keywords for Cosmic Microwave Background Radiation. The keywords used were as follows: 

cosmic microwave background
OR
CMB

The baseline time span for this database is 1996-August 31, 2006. The resulting database contained 3,811 (10 years) and  1,316 (2 years) papers; 5,027 authors; 58 countries; 313 journals; and 1,311 institutions.

Rankings

Once the database was in place, it was used to generate the lists of top 20 papers (two- and ten-year periods), authors, journals, institutions, and nations, covering a time span of 1996-August 31, 2006 (fourth bimonthly, ten-year plus eight-month period).

The top 20 papers are ranked according to total cites. Rankings for author, journal, institution, and country are listed in three ways: according to total cites, total papers, and total cites/paper. The paper thresholds and corresponding percentages used to determine scientist, institution, country, and journal rankings according to total cites/paper, and total papers respectively are as follows:

Entity:	Scientists	Institutions	Countries	Journals
Thresholds:	29	15	24	18
Percentage:	1%	10%	50%	10%

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