Editing Very Small Array (section)

== Results ==
[[Image:WMAP TT power spectrum.png|thumb|right|300px|The power spectrum of the cosmic microwave background radiation temperature anisotropy in terms of the angular scale (or [[multipole moment]]). The data shown come from the [[WMAP]] (2006), [[Arcminute Cosmology Bolometer Array Receiver|Acbar]] (2004) [[BOOMERanG experiment|Boomerang]] (2005), [[Cosmic Background Imager|CBI]] (2004) and Very Small Array (2004) instruments.]]

The fields observed with the VSA were chosen to minimize the amount of bright radio sources and large clusters in the field (the latter to avoid the [[Sunyaev-Zel'dovich effect]]), as well as to avoid contamination by emission from [[Milky Way|our galaxy]].<ref name="dickinson" /> The radio point sources present in the VSA fields were observed with the [[Ryle Telescope]] at 15&nbsp;GHz, then monitored by the VSA source subtracters during the VSA observations.<ref name="watson" />

In the compact array configuration, the telescope observed three 7×7 degree areas of the sky to high precision<ref name="cam" /> in an observing session between August 2000 and August 2001.<ref name="maisinger" /> These observations were taken at the highest frequency of the telescope, centered at 34&nbsp;GHz, to reduce foreground contamination.<ref name="taylor" /> Another, larger area of the sky was also observed, but less precisely.<ref name="taylor" /> The data from these observations were reduced independently at all three involved institutions.<ref name="jbo_dev" /> The results from these observations were published in a series of four papers in 2003; those by Watson et al., Taylor et al., Scott et al. and Rubino-Martin et al. (see References below). The key results were the power spectra of the [[Cosmic Microwave Background]] between multipoles of 150 and 900,<ref name="scott" /> and the resulting limits on [[Lambda-CDM model#Parameters|cosmological parameters]] when combined with data from observations from other experiments.<ref name="rubino" />

The second observing session ran between September 2001<ref name="maisinger" /> and July 2003, and was using the extended array.<ref name="vsaextendedobs" /> The first results from the extended array were published as a Letter in 2003, simultaneously with the first four publications, using data taken up until April 2002. The sections of the sky observed were located within the previously-observed fields, with the measurements being both more accurate and in greater detail. The result was an improved power spectrum of the CMB, going out to a multipole of 1400,<ref name="grainge" /> and refined cosmological parameters.<ref name="slosar" /> The second set of results were published in 2004, and consisted of the original observations plus more observations taken in the same regions of the sky, as well as observations in three new regions. This yielded measurements of the CMB power spectra out to l of 1500 much more accurately than previously,<ref name="dickinson" /> and more accurate cosmological parameter estimates.<ref name="rebolo" />

Observations with the VSA continued until the end of August 2008, using the Super-Extended configuration. Also, the Ryle Telescope has been upgraded to detect lower flux point sources, and the OCRA receiver on a telescope in Poland will be used to more accurately subtract the point sources.<ref name="cleary" />

{| class="wikitable"
|- style="text-align:center;"
| [[Image:VSA CMB spectra 1.png|250px|First results.<ref name="scott" />]]
| [[Image:VSA spectra 2.png|250px|Second results.<ref name="grainge" />]]
| [[Image:VSA spectra 3.png|250px|Third results.<ref name="dickinson" />]]
|-
| colspan=3 | The Very Small Array's measurements of the [[Cosmic Microwave Background|CMB]] power spectra. From left to right: from first observations,<ref name="scott" /> the first results from the second observing session<ref name="grainge" /> and the final results from the second observing session.<ref name="dickinson" />
|}