Interferometry is the technique of combining two electromagnetic waves aligned in such a way that they increase their amplitude (and hence their visibility). A beam splitter is used to cut the incoming frequency (could be laser, starlight or radio wave) in half, and then with mirrors, to bring the two waves together. http://www.space.com/scienceastronomy/astronomy/interferometry_101.html There are a number of different types of interferometers, such as Fizeau, Michelson, Twyman-Green and Mach-Zehnder. http://docs.google.com/viewer?a=v&q=cache:EhQiK86DrC8J:www.optics.arizona.edu/jcwyant/Short_Courses/SIRA/2-BasicInterferometryAndOpticalTesting.pdf+interferometry+basics&hl=en&gl=us&pid=bl&srcid=ADGEESjNBlHvUv9yPOAOxWelulIAgZ-Cb_NBJeiiV1kkryiymR3s8mamlY-v3JMJFTtlWRa6SswZNhBqTcnqSIRF4pFAtWm_MeK9N3oIG3wZM7vq_So0uIJBchhlVf0SLg4jmJfVGbr8&sig=AHIEtbQYMxhxUEIpYwZURTx15yMSFMLY9wInterferometry is an important tool for physics because light sources such as stars and radio signals may be too faint or blurry to thoroughly analyze. http://www.europhysicsnews.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/epn/pdf/2001/06/epn01613.pdfhttp://outreach.atnf.csiro.au/education/senior/astrophysics/interferometry.html#interfoptical An interferometer was used in the Michelson-Morely Experiment to disprove the existence of ether. http://planetquest.jpl.nasa.gov/technology/michelson.cfm

Interferometry is used in astronomy to obtain the size of stars and planets.http://www.europhysicsnews.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/epn/pdf/2001/06/epn01613.pdf In 1891, Michelson was able to successfully measure the diameters of the moons around Jupiter. http://www.europhysicsnews.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/epn/pdf/2001/06/epn01613.pdf More recently, it has been used for searching for Extra-Solar Planets. http://planetquest.jpl.nasa.gov/technology/technology_index.cfmInterferometers can have a wider viewing angle and more precision (down to 20 microarcseconds) than other search methods. http://www.europhysicsnews.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/epn/pdf/2001/06/epn01613.pdf The Space Interferometry Mission, or SIM, is a project worked on by NASA where a satellite interferometer will be searching for planets around other stars from space. http://sim.jpl.nasa.gov/index.cfm However, due to government budget cuts, this project has been postponed. http://search.nasa.gov/search/search.jsp?nasaInclude=2008+SIM+project+postponed&entqr=0&output=xml_no_dtd&sort=date%3AD%3AL%3Ad1&ud=1&site=nasa_collection&client=nasa_production&ie=UTF-8&oe=UTF-8&simple_start=&news_start=&images_start=&videos_start=&podcasts_start=&baynote_start=&baynoteOrGSA=baynote

When two light waves interfere, they combine depending on what phase they are in. If one wave's peak is aligned with the other's trough, they cancel each other out (destructive interference). However, if both peaks and troughs are aligned, then a new wave will be formed with a greater amplitude (constructive interference).http://www.space.com/scienceastronomy/astronomy/interferometry_101.html The amplitude will increase by the sum of the original two amplitudes plus double the square root of the multiplication of both amplitudes. http://docs.google.com/viewer?a=v&q=cache:EhQiK86DrC8J:www.optics.arizona.edu/jcwyant/Short_Courses/SIRA/2-BasicInterferometryAndOpticalTesting.pdf+interferometry+basics&hl=en&gl=us&pid=bl&srcid=ADGEESjNBlHvUv9yPOAOxWelulIAgZ-Cb_NBJeiiV1kkryiymR3s8mamlY-v3JMJFTtlWRa6SswZNhBqTcnqSIRF4pFAtWm_MeK9N3oIG3wZM7vq_So0uIJBchhlVf0SLg4jmJfVGbr8&sig=AHIEtbQYMxhxUEIpYwZURTx15yMSFMLY9w

In an interferometer, the path of both waves is constructed in such a way to maximize the amplitude. http://outreach.atnf.csiro.au/education/senior/astrophysics/interferometry.html#interfoptical http://www.europhysicsnews.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/epn/pdf/2001/06/epn01613.pdf The wave, after interference, is displayed as a series of dark and bright lines. http://docs.google.com/viewer?a=v&q=cache:EhQiK86DrC8J:www.optics.arizona.edu/jcwyant/Short_Courses/SIRA/2-BasicInterferometryAndOpticalTesting.pdf+interferometry+basics&hl=en&gl=us&pid=bl&srcid=ADGEESjNBlHvUv9yPOAOxWelulIAgZ-Cb_NBJeiiV1kkryiymR3s8mamlY-v3JMJFTtlWRa6SswZNhBqTcnqSIRF4pFAtWm_MeK9N3oIG3wZM7vq_So0uIJBchhlVf0SLg4jmJfVGbr8&sig=AHIEtbQYMxhxUEIpYwZURTx15yMSFMLY9w Most people are familiar with this as the "slit" experiment. http://www.space.com/scienceastronomy/astronomy/interferometry_101.html The slits will be brighter than the original beam. Many different aberrations can occur in the resulting pattern, which can be due to a number of different factors, such as the symmetry of the interferometer, thermal expansion, pressure from securing elements to the apparatus or even the force of gravity. http://docs.google.com/viewer?a=v&q=cache:EhQiK86DrC8J:www.optics.arizona.edu/jcwyant/Short_Courses/SIRA/2-BasicInterferometryAndOpticalTesting.pdf+aberrations+in+interferometry+basics&hl=en&gl=us&pid=bl&srcid=ADGEESjNBlHvUv9yPOAOxWelulIAgZ-Cb_NBJeiiV1kkryiymR3s8mamlY-v3JMJFTtlWRa6SswZNhBqTcnqSIRF4pFAtWm_MeK9N3oIG3wZM7vq_So0uIJBchhlVf0SLg4jmJfVGbr8&sig=AHIEtbSRHG8Wg5Noxxl89PP4uoZ8SNAkNghttp://www.telescope-optics.net/induced2.htm