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The Wilkinson Microwave Anisotropy Probe (WMAP), originally known as the Microwave Anisotropy Probe (MAP and Explorer 80), was a NASA spacecraft operating from 2001 to 2010 which measured temperature differences across the sky in the cosmic microwave background (CMB) – the radiant heat remaining from the
Big Bang The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...
. Headed by Professor Charles L. Bennett of Johns Hopkins University, the mission was developed in a joint partnership between the NASA
Goddard Space Flight Center The Goddard Space Flight Center (GSFC) is a major NASA space research laboratory located approximately northeast of Washington, D.C. in Greenbelt, Maryland, United States. Established on May 1, 1959 as NASA's first space flight center, GSFC empl ...
and Princeton University. The WMAP spacecraft was launched on 30 June 2001 from Florida. The WMAP mission succeeded the COBE space mission and was the second medium-class (MIDEX) spacecraft in the NASA Explorer program. In 2003, MAP was renamed WMAP in honor of cosmologist
David Todd Wilkinson David Todd Wilkinson (13 May 1935 – 5 September 2002) was an American cosmologist, specializing in the study of the cosmic microwave background radiation ( CMB) left over from the Big Bang. Education He was born in Hillsdale, Michigan, an ...
(1935–2002), who had been a member of the mission's science team. After nine years of operations, WMAP was switched off in 2010, following the launch of the more advanced Planck spacecraft by
European Space Agency , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1205 ...
(ESA) in 2009. WMAP's measurements played a key role in establishing the current Standard Model of Cosmology: the
Lambda-CDM model The ΛCDM (Lambda cold dark matter) or Lambda-CDM model is a parameterization of the Big Bang cosmological model in which the universe contains three major components: first, a cosmological constant denoted by Lambda (Greek Λ) associated with d ...
. The WMAP data are very well fit by a universe that is dominated by dark energy in the form of a cosmological constant. Other cosmological data are also consistent, and together tightly constrain the Model. In the Lambda-CDM model of the universe, the age of the universe is billion years. The WMAP mission's determination of the age of the universe is to better than 1% precision. The current expansion rate of the universe is (see Hubble constant) . The content of the universe currently consists of ordinary baryonic matter;
cold dark matter In cosmology and physics, cold dark matter (CDM) is a hypothetical type of dark matter. According to the current standard model of cosmology, Lambda-CDM model, approximately 27% of the universe is dark matter and 68% is dark energy, with only a sm ...
(CDM) that neither emits nor absorbs light; and of dark energy in the form of a cosmological constant that accelerates the
expansion of the universe The expansion of the universe is the increase in distance between any two given gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion whereby the scale of space itself changes. The universe does not exp ...
. Less than 1% of the current content of the universe is in neutrinos, but WMAP's measurements have found, for the first time in 2008, that the data prefer the existence of a cosmic neutrino backgroundHinshaw et al. (2009) with an effective number of neutrino species of . The contents point to a Euclidean flat geometry, with curvature (\Omega_) of . The WMAP measurements also support the
cosmic inflation In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from  seconds after the conjectured Big Bang singularity ...
paradigm in several ways, including the flatness measurement. The mission has won various awards: according to ''Science'' magazine, the WMAP was the ''Breakthrough of the Year for 2003''.Seife (2003) This mission's results papers were first and second in the "Super Hot Papers in Science Since 2003" list. Of the all-time most referenced papers in physics and astronomy in the
INSPIRE-HEP INSPIRE-HEP is an open access digital library for the field of high energy physics (HEP). It is the successor of the Stanford Physics Information Retrieval System (SPIRES) database, the main literature database for high energy physics since the 1970 ...
database, only three have been published since 2000, and all three are WMAP publications. Bennett, Lyman A. Page Jr., and David N. Spergel, the latter both of Princeton University, shared the 2010
Shaw Prize The Shaw Prize is an annual award presented by the Shaw Prize Foundation. Established in 2002 in Hong Kong, it honours "individuals who are currently active in their respective fields and who have recently achieved distinguished and signifi ...
in astronomy for their work on WMAP. Bennett and the WMAP science team were awarded the 2012 Gruber Prize in cosmology. The 2018 Breakthrough Prize in Fundamental Physics was awarded to Bennett, Gary Hinshaw, Norman Jarosik, Page, Spergel, and the WMAP science team. In October 2010, the WMAP spacecraft was derelict in a
heliocentric Heliocentrism (also known as the Heliocentric model) is the astronomical model in which the Earth and planets revolve around the Sun at the center of the universe. Historically, heliocentrism was opposed to geocentrism, which placed the Earth at ...
graveyard orbit after completing 9 years of operations. All WMAP data are released to the public and have been subject to careful scrutiny. The final official data release was the nine-year release in 2012. Some aspects of the data are statistically unusual for the Standard Model of Cosmology. For example, the largest angular-scale measurement, the quadrupole moment, is somewhat smaller than the Model would predict, but this discrepancy is not highly significant. A large
cold spot Cold spot may refer to: * Cold spot (paranormal), an area of low temperature that allegedly indicates the presence of a ghost * CMB cold spot The CMB Cold Spot or WMAP Cold Spot is a region of the sky seen in microwaves that has been found to ...
and other features of the data are more statistically significant, and research continues into these.


Objectives

The WMAP objective was to measure the temperature differences in the Cosmic Microwave Background (CMB) radiation. The anisotropies then were used to measure the universe's geometry, content, and evolution; and to test the
Big Bang The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...
model, and the
cosmic inflation In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from  seconds after the conjectured Big Bang singularity ...
theory. For that, the mission created a full-sky map of the CMB, with a 13
arcminutes A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The na ...
resolution via multi-frequency observation. The map required the fewest
systematic error Observational error (or measurement error) is the difference between a measured value of a quantity and its true value.Dodge, Y. (2003) ''The Oxford Dictionary of Statistical Terms'', OUP. In statistics, an error is not necessarily a " mistak ...
s, no correlated pixel noise, and accurate calibration, to ensure angular-scale accuracy greater than its resolution.Bennett et al. (2003a) The map contains 3,145,728 pixels, and uses the
HEALPix HEALPix (sometimes written as Healpix), an acronym for Hierarchical Equal Area isoLatitude Pixelisation of a 2-sphere, is an algorithm for pixelisation of the 2-sphere and the associated class of map projections. The pixelisation algorithm was de ...
scheme to pixelize the sphere.Bennett et al. (2003b) The telescope also measured the CMB's E-mode polarization, and foreground polarization. Its service life was 27 months; 3 to reach the position, and 2 years of observation.


Development

The MAP mission was proposed to NASA in 1995, selected for definition study in 1996, and approved for development in 1997. The WMAP was preceded by two missions to observe the CMB; (i) the Soviet RELIKT-1 that reported the upper-limit measurements of CMB anisotropies, and (ii) the U.S. COBE satellite that first reported large-scale CMB fluctuations. The WMAP was 45 times more sensitive, with 33 times the angular resolution of its COBE satellite predecessor.Limon et al. (2008) The successor European Planck mission (operational 2009–2013) had a higher resolution and higher sensitivity than WMAP and observed in 9 frequency bands rather than WMAP's 5, allowing improved astrophysical foreground models.


Spacecraft

The telescope's primary reflecting mirrors are a pair of Gregorian dishes (facing opposite directions), that focus the signal onto a pair of secondary reflecting mirrors. They are shaped for optimal performance: a carbon fibre shell upon a Korex core, thinly-coated with aluminium and
silicon oxide Silicon oxide may refer to either of the following: *Silicon dioxide or quartz, SiO2, very well characterized *Silicon monoxide Silicon monoxide is the chemical compound with the formula SiO where silicon is present in the oxidation state +2. In ...
. The secondary reflectors transmit the signals to the corrugated feedhorns that sit on a
focal plane In Gaussian optics, the cardinal points consist of three pairs of points located on the optical axis of a rotationally symmetric, focal, optical system. These are the '' focal points'', the principal points, and the nodal points. For ''ideal'' ...
array box beneath the primary reflectors. The receivers are
polarization Polarization or polarisation may refer to: Mathematics *Polarization of an Abelian variety, in the mathematics of complex manifolds *Polarization of an algebraic form, a technique for expressing a homogeneous polynomial in a simpler fashion by ...
-sensitive differential
radiometer A radiometer or roentgenometer is a device for measuring the radiant flux (power) of electromagnetic radiation. Generally, a radiometer is an infrared radiation detector or an ultraviolet detector. Microwave radiometers operate in the microwave w ...
s measuring the difference between two telescope beams. The signal is amplified with High-electron-mobility transistor (HEMT)
low-noise amplifier A low-noise amplifier (LNA) is an electronic amplifier that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio. An amplifier will increase the power of both the signal and the noise present at its input, ...
s, built by the
National Radio Astronomy Observatory The National Radio Astronomy Observatory (NRAO) is a federally funded research and development center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc. for the purpose of radio a ...
(NRAO). There are 20 feeds, 10 in each direction, from which a radiometer collects a signal; the measure is the difference in the sky signal from opposite directions. The directional separation azimuth is 180°; the total angle is 141°. To improve subtraction of foreground signals from our Milky Way galaxy, the WMAP used five discrete radio frequency bands, from 23 GHz to 94 GHz. The WMAP's base is a -diameter
solar panel A solar cell panel, solar electric panel, photo-voltaic (PV) module, PV panel or solar panel is an assembly of photovoltaic solar cells mounted in a (usually rectangular) frame, and a neatly organised collection of PV panels is called a photo ...
array that keeps the instruments in shadow during CMB observations, (by keeping the craft constantly angled at 22°, relative to the Sun). Upon the array sit a bottom deck (supporting the warm components) and a top deck. The telescope's cold components: the focal-plane array and the mirrors, are separated from the warm components with a cylindrical, -long thermal isolation shell atop the deck. Passive thermal radiators cool the WMAP to approximately ; they are connected to the
low-noise amplifier A low-noise amplifier (LNA) is an electronic amplifier that amplifies a very low-power signal without significantly degrading its signal-to-noise ratio. An amplifier will increase the power of both the signal and the noise present at its input, ...
s. The telescope consumes 419 W of power. The available telescope heaters are emergency-survival heaters, and there is a transmitter heater, used to warm them when off. The WMAP spacecraft's temperature is monitored with
platinum resistance thermometer Resistance thermometers, also called resistance temperature detectors (RTDs), are sensors used to measure temperature. Many RTD elements consist of a length of fine wire wrapped around a heat-resistant ceramic or glass core but other constructi ...
s. The WMAP's calibration is effected with the CMB dipole and measurements of Jupiter; the beam patterns are measured against Jupiter. The telescope's data are relayed daily via a 2-GHz transponder providing a 667 kbit/s downlink to a Deep Space Network station. The spacecraft has two transponders, one a redundant backup; they are minimally active – about 40 minutes daily – to minimize radio frequency interference. The telescope's position is maintained, in its three axes, with three
reaction wheel A reaction wheel (RW) is used primarily by spacecraft for three-axis attitude control, and does not require rockets or external applicators of torque. They provide a high pointing accuracy, and are particularly useful when the spacecraft must be ...
s,
gyroscope A gyroscope (from Ancient Greek γῦρος ''gŷros'', "round" and σκοπέω ''skopéō'', "to look") is a device used for measuring or maintaining orientation and angular velocity. It is a spinning wheel or disc in which the axis of rota ...
s, two star trackers and sun sensors, and is steered with eight
hydrazine Hydrazine is an inorganic compound with the chemical formula . It is a simple pnictogen hydride, and is a colourless flammable liquid with an ammonia-like odour. Hydrazine is highly toxic unless handled in solution as, for example, hydrazine ...
thrusters.


Launch, trajectory, and orbit

The WMAP spacecraft arrived at the Kennedy Space Center on 20 April 2001. After being tested for two months, it was launched via Delta II 7425 launch vehicle on 30 June 2001. It began operating on its internal power five minutes before its launching, and continued so operating until the solar panel array deployed. The WMAP was activated and monitored while it cooled. On 2 July 2001, it began working, first with in-flight testing (from launching until 17 August 2001), then began constant, formal work. Afterwards, it effected three Earth-Moon phase loops, measuring its sidelobes, then flew by the Moon on 30 July 2001, en route to the Sun-Earth
Lagrange point In celestial mechanics, the Lagrange points (; also Lagrangian points or libration points) are points of equilibrium for small-mass objects under the influence of two massive orbiting bodies. Mathematically, this involves the solution of th ...
, arriving there on 1 October 2001, becoming the first CMB observation mission posted there. Locating the spacecraft at Lagrange 2, ( from Earth) thermally stabilizes it and minimizes the contaminating solar, terrestrial, and lunar emissions registered. To view the entire sky, without looking to the Sun, the WMAP traces a path around in a
Lissajous orbit In orbital mechanics, a Lissajous orbit (), named after Jules Antoine Lissajous, is a quasi-periodic orbital trajectory that an object can follow around a Lagrangian point of a three-body system without requiring any propulsion. Lyapunov orbits ...
ca. 1.0° to 10°, with a 6-month period. The telescope rotates once every 2 minutes 9 seconds (0.464
rpm Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines. Standards ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...
) and precesses at the rate of 1 revolution per hour. WMAP measured the entire sky every six months, and completed its first, full-sky observation in April 2002. File:WMAP launch.jpg, WMAP launches from Kennedy Space Center, 30 June 2001 File:WMAP trajectory and orbit.jpg, The WMAP's trajectory and orbit File:WMAP orbit.jpg, WMAP's orbit and sky scan strategy


Experiment


Pseudo-Correlation Radiometer

The WMAP instrument consists of pseudo-correlation differential radiometers fed by two back-to-back primary Gregorian reflectors. This instrument uses five frequency bands from 22 GHz to 90 GHz to facilitate rejection of foreground signals from our own Galaxy. The WMAP instrument has a 3.5° x 3.5° field of view (FoV).


Foreground radiation subtraction

The WMAP observed in five frequencies, permitting the measurement and subtraction of foreground contamination (from the Milky Way and extra-galactic sources) of the CMB. The main emission mechanisms are
synchrotron radiation Synchrotron radiation (also known as magnetobremsstrahlung radiation) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in ...
and
free-free emission ''Bremsstrahlung'' (), from "to brake" and "radiation"; i.e., "braking radiation" or "deceleration radiation", is electromagnetic radiation produced by the deceleration of a charged particle when deflected by another charged particle, typicall ...
(dominating the lower frequencies), and
astrophysical dust Cosmic dust, also called extraterrestrial dust, star dust or space dust, is dust which exists in outer space, or has fallen on Earth. Most cosmic dust particles measure between a few molecules and 0.1 mm (100 micrometers). Larger particles are c ...
emissions (dominating the higher frequencies). The spectral properties of these emissions contribute different amounts to the five frequencies, thus permitting their identification and subtraction. Foreground contamination is removed in several ways. First, subtract extant emission maps from the WMAP's measurements; second, use the components' known spectral values to identify them; third, simultaneously fit the position and spectra data of the foreground emission, using extra data sets. Foreground contamination was reduced by using only the full-sky map portions with the least foreground contamination, while masking the remaining map portions.


Measurements and discoveries


One-year data release

On 11 February 2003, NASA published the first-year's worth of WMAP data. The latest calculated age and composition of the early universe were presented. In addition, an image of the early universe, that "contains such stunning detail, that it may be one of the most important scientific results of recent years" was presented. The newly released data surpass previous CMB measurements. Based upon the
Lambda-CDM model The ΛCDM (Lambda cold dark matter) or Lambda-CDM model is a parameterization of the Big Bang cosmological model in which the universe contains three major components: first, a cosmological constant denoted by Lambda (Greek Λ) associated with d ...
, the WMAP team produced cosmological parameters from the WMAP's first-year results. Three sets are given below; the first and second sets are WMAP data; the difference is the addition of spectral indices, predictions of some inflationary models. The third data set combines the WMAP constraints with those from other CMB experiments (
ACBAR ACBAR was an experiment to measure the anisotropy of the Cosmic microwave background. It was active 2000-2008. The ACBAR 145 GHz measurements were the most precise high multipole measurements of the CMB at the time. See also *Cosmic microwa ...
and CBI), and constraints from the
2dF Galaxy Redshift Survey In astronomy, the 2dF Galaxy Redshift Survey (Two-degree-Field Galaxy Redshift Survey), 2dF or 2dFGRS is a redshift survey conducted by the Australian Astronomical Observatory (AAO) with the 3.9m Anglo-Australian Telescope between 1997 and 11 A ...
and
Lyman alpha forest Lyman may refer to: Places Ukraine * Lyman, Ukraine United States * Lyman, Iowa * Lyman, Maine * Lyman, Mississippi * Lyman, Nebraska * Lyman, New Hampshire * Lyman, Oklahoma * Lyman, South Carolina * Lyman, South Dakota * Lyman County, South Dak ...
measurements. There are degenerations among the parameters, the most significant is between n_s and \tau; the errors given are at 68% confidence. Using the best-fit data and theoretical models, the WMAP team determined the times of important universal events, including the redshift of reionization, ; the redshift of decoupling, (and the universe's age at decoupling, ); and the redshift of matter/radiation equality, . They determined the thickness of the surface of last scattering to be in redshift, or . They determined the current density of baryons, , and the ratio of baryons to photons, . The WMAP's detection of an early reionization excluded warm dark matter. The team also examined Milky Way emissions at the WMAP frequencies, producing a 208- point source catalogue.


Three-year data release

The three-year WMAP data were released on 17 March 2006. The data included temperature and polarization measurements of the CMB, which provided further confirmation of the standard flat Lambda-CDM model and new evidence in support of inflation. The 3-year WMAP data alone shows that the universe must have dark matter. Results were computed both only using WMAP data, and also with a mix of parameter constraints from other instruments, including other CMB experiments (
Arcminute Cosmology Bolometer Array Receiver ACBAR was an experiment to measure the anisotropy of the Cosmic microwave background. It was active 2000-2008. The ACBAR 145 GHz measurements were the most precise high multipole measurements of the CMB at the time. See also *Cosmic microwa ...
(ACBAR),
Cosmic Background Imager The Cosmic Background Imager (or CBI) was a 13-element interferometer perched at an elevation of 5,080 metres (16,700 feet) at Llano de Chajnantor Observatory in the Chilean Andes. It started operations in 1999 to study the cosmic microwave bac ...
(CBI) and BOOMERANG),
Sloan Digital Sky Survey The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project began in 2000 a ...
(SDSS), the
2dF Galaxy Redshift Survey In astronomy, the 2dF Galaxy Redshift Survey (Two-degree-Field Galaxy Redshift Survey), 2dF or 2dFGRS is a redshift survey conducted by the Australian Astronomical Observatory (AAO) with the 3.9m Anglo-Australian Telescope between 1997 and 11 A ...
, the
Supernova Legacy Survey The Supernova Legacy Survey Program is a project designed to investigate dark energy, by detecting and monitoring approximately 2000 high-redshift supernovae between 2003 and 2008, using MegaPrime, a large CCD mosaic at the Canada-France-Hawaii ...
and constraints on the Hubble constant from the Hubble Space Telescope. Optical depth to reionization improved due to polarization measurements.Hinshaw et al. (2007)
<0.30 when combined with SDSS data. No indication of non-gaussianity.


Five-year data release

The five-year WMAP data were released on 28 February 2008. The data included new evidence for the cosmic neutrino background, evidence that it took over half billion years for the first stars to reionize the universe, and new constraints on
cosmic inflation In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch lasted from  seconds after the conjectured Big Bang singularity ...
. The improvement in the results came from both having an extra 2 years of measurements (the data set runs between midnight on 10 August 2001 to midnight of 9 August 2006), as well as using improved data processing techniques and a better characterization of the instrument, most notably of the beam shapes. They also make use of the 33-GHz observations for estimating cosmological parameters; previously only the 41-GHz and 61-GHz channels had been used. Improved masks were used to remove foregrounds. Improvements to the spectra were in the 3rd acoustic peak, and the polarization spectra. The measurements put constraints on the content of the universe at the time that the CMB was emitted; at the time 10% of the universe was made up of neutrinos, 12% of atoms, 15% of photons and 63% dark matter. The contribution of dark energy at the time was negligible. It also constrained the content of the present-day universe; 4.6% atoms, 23% dark matter and 72% dark energy. The WMAP five-year data was combined with measurements from Type Ia supernova (SNe) and Baryon acoustic oscillations (BAO). The elliptical shape of the WMAP skymap is the result of a Mollweide projection.WMAP 1-year Paper Figures
Bennett, et al.
The data puts limits on the value of the tensor-to-scalar ratio, r <0.22 (95% certainty), which determines the level at which gravitational waves affect the polarization of the CMB, and also puts limits on the amount of primordial non-gaussianity. Improved constraints were put on the redshift of reionization, which is , the redshift of decoupling, (as well as age of universe at decoupling, ) and the redshift of matter/radiation equality, . The
extragalactic Extragalactic astronomy is the branch of astronomy concerned with objects outside the Milky Way galaxy. In other words, it is the study of all astronomical objects which are not covered by galactic astronomy. The closest objects in extragalactic ...
source catalogue was expanded to include 390 sources, and variability was detected in the emission from Mars and
Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
.


Seven-year data release

The seven-year WMAP data were released on 26 January 2010. As part of this release, claims for inconsistencies with the standard model were investigated. Most were shown not to be statistically significant, and likely due to ''a posteriori'' selection (where one sees a weird deviation, but fails to consider properly how hard one has been looking; a deviation with 1:1000 likelihood will typically be found if one tries one thousand times). For the deviations that do remain, there are no alternative cosmological ideas (for instance, there seem to be correlations with the ecliptic pole). It seems most likely these are due to other effects, with the report mentioning uncertainties in the precise beam shape and other possible small remaining instrumental and analysis issues. The other confirmation of major significance is of the total amount of matter/energy in the universe in the form of dark energy – 72.8% (within 1.6%) as non 'particle' background, and dark matter – 22.7% (within 1.4%) of non baryonic (sub-atomic) 'particle' energy. This leaves matter, or baryonic particles (atoms) at only 4.56% (within 0.16%).


Nine-year data release

On 29 December 2012, the nine-year WMAP data and related images were released. billion-year-old temperature fluctuations and a temperature range of ± 200 micro kelvins are shown in the image. In addition, the study found that 95% of the early universe is composed of dark matter and dark energy, the curvature of space is less than 0.4% of "flat" and the universe emerged from the cosmic Dark Ages "about 400 million years" after the
Big Bang The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...
.Hinshaw, et al., 2013
/ref>


Main result

The main result of the mission is contained in the various oval maps of the CMB temperature differences. These oval images present the temperature distribution derived by the WMAP team from the observations by the telescope during the mission. Measured is the temperature obtained from a
Planck's law In physics, Planck's law describes the spectral density of electromagnetic radiation emitted by a black body in thermal equilibrium at a given temperature , when there is no net flow of matter or energy between the body and its environment. At ...
interpretation of the microwave background. The oval map covers the whole sky. The results are a snapshot of the universe around 375,000 years after the
Big Bang The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...
, which happened about 13.8 billion years ago. The microwave background is very homogeneous in temperature (the relative variations from the mean, which presently is still 2.7 kelvins, are only of the order of ). The temperature variations corresponding to the local directions are presented through different colors (the "red" directions are hotter, the "blue" directions cooler than the average).


Follow-on missions and future measurements

The original timeline for WMAP gave it two years of observations; these were completed by September 2003. Mission extensions were granted in 2002, 2004, 2006, and 2008 giving the spacecraft a total of 9 observing years, which ended August 2010 and in October 2010 the spacecraft was moved to a heliocentric "graveyard" orbit. The Planck spacecraft also measured the CMB from 2009 to 2013 and aims to refine the measurements made by WMAP, both in total intensity and polarization. Various ground- and balloon-based instruments have also made CMB contributions, and others are being constructed to do so. Many are aimed at searching for the B-mode polarization expected from the simplest models of inflation, including
The E and B Experiment The E and B Experiment (EBEX) will measure the cosmic microwave background radiation of a part of the sky during two sub-orbital (high-altitude) balloon flights. It is an experiment to make large, high-fidelity images of the CMB polarization aniso ...
(EBEX), Spider, BICEP and Keck Array (BICEP2), Keck,
QUIET Quiet may refer to: * Silence, a relative or total lack of sound In music * The Quiett (born 1985), South Korean rapper * ''Quiet'' (album), a 1996 John Scofield album * "Quiet", a song by Lights, from her album '' The Listening'' (2009) * "Qui ...
,
Cosmology Large Angular Scale Surveyor The Cosmology Large Angular Scale Surveyor (CLASS) is an array of microwave telescopes at a high-altitude site in the Atacama Desert of Chile as part of the Parque Astronómico de Atacama. The CLASS experiment aims to improve our understanding of c ...
(CLASS), South Pole Telescope (SPTpol) and others. On 21 March 2013, the European-led research team behind the Planck spacecraft released the mission's all-sky map of the cosmic microwave background. The map suggests the universe is slightly older than previously thought. According to the map, subtle fluctuations in temperature were imprinted on the deep sky when the cosmos was about 370,000 years old. The imprint reflects ripples that arose as early, in the existence of the universe, as the first nonillionth (10−30) of a second. Apparently, these ripples gave rise to the present vast cosmic web of galaxy clusters and dark matter. Based on the 2013 data, the universe contains 4.9%
ordinary matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic par ...
, 26.8% dark matter and 68.3% dark energy. On 5 February 2015, new data was released by the Planck mission, according to which the age of the universe is 13.799 ± 0.021 billion years and the Hubble constant is 67.74 ± 0.46 (km/s)/Mpc.


See also

* Explorer program *
Illustris project The Illustris project was a series of astrophysical simulations run by an international collaboration of scientists. The aim was to study the processes of galaxy formation and evolution in the universe with a comprehensive physical model. Early r ...
* List of cosmic microwave background experiments *
List of cosmological computation software The cosmic microwave background (CMB) is the thermal radiation assumed to be left over from the " Big Bang" of cosmology. The CMB is a snapshot of the oldest light in our universe, imprinted on the sky when the universe was just 380,000 years ol ...
*
S150 Galactic X-Ray Mapping Skylab 3 (also SL-3 and SLM-2) was the second crewed mission to the first American space station, Skylab. The mission began on July 28, 1973, with the launch of NASA astronauts Alan Bean, Owen Garriott, and Jack Lousma in the Apollo command an ...


References


Primary sources

* * * * * * * * *


Further reading

*


External links


Sizing up the universe

Big Bang glow hints at funnel-shaped Universe
New Scientist, 15 April 2004
NASA 16 March 2006 WMAP inflation related press release
* {{Authority control Articles containing video clips Artificial satellites at Earth-Sun Lagrange points Cosmic microwave background experiments Derelict satellites in heliocentric orbit Explorers Program NASA space probes Space probes launched in 2001 Space telescopes Spacecraft launched by Delta II rockets Spacecraft using Lissajous orbits