This was somewhat disquieting — if the universe was so smooth, how and when did the seeds of the first structures form? Astronomers began work on instruments that would bring the snapshot into sharper focus. CMB radiation is so weak that Earth’s atmosphere muddies the signal. So in 1989, NASA launched a satellite to study it. In 1992, results from this mission, called the Cosmic Background Explorer (COBE), rocked the astronomical community.
Other experiments to measure the CMB are conducted in environments that minimize the atmosphere’s obscuring effects, such as on balloons and in high and dry regions.
The BOOMERANG (Balloon Observations of Millimetric Extragalactic Radiation and Geophysics) experiment flew in a circle 120,000 feet (37 kilometers) above Antarctica from December 29, 1998, to January 9, 1999. An international collaboration, BOOMERANG created a map of the CMB at least 40 times more detailed than COBE’s, and witnessed harmonic-type peaks in the radiation predicted by inflation theory.
A second international balloon experiment called MAXIMA (Millimeter Anisotropy Experiment Imaging Array) completed two successful flights over Texas in 1998 and 1999. It studied the CMB at even smaller angular scales than BOOMERANG and confirmed the other experiment’s results.
In 2001, NASA launched the Microwave Anisotropy Probe (MAP) to study the CMB in unprecedented detail. Data from this space mission is expected to be released in January 2003.
Other projects which have also used multiple, connected detectors, known as interferometers, to study the CMB include:
The Cosmic Anisotropy Telescope (CAT), based near Cambridge, England. The first interferometer to study the CMB, it began taking measurements in 1993 but was partially dismantled in 2000.
The ATCA Cosmic Microwave Background Radiation Anisotropy Experiment, based in Narrabri, Australia. Composed of five dishes which are each 22 meters across, it has been taking data since 1991 at a resolution of 2 arcminutes.
The Cosmic Background Imager (CBI), located in Chile’s Atacama desert. It is composed of 13 elements and began its measurements of the CMB in 1999.
The Very Small Array (VSA), located in Tenerife, Spain. Its 14 components can resolve objects between the angular sizes of 0.2° and 3° (the full moon is 0.5°). It began taking data in 2000.