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The transit method can be used to discover [[exoplanet]]s. As a planet eclipses/transits its host star it will block a portion of the light from the star. If the planet transits in-between the star and the observer the change in light can be measured to construct a [[light curve]]. Light curves are measured with a [[Charge-coupled device|charged-coupled device]]. The light curve of a star can disclose several physical characteristics of the planet and star, such as, density. Multiple transit events must be measured to determine the characteristics which tend to occur at regular intervals. Multiple planets orbiting the same host star can cause [[Transit-timing variation|Transit Time Variations(TTV).]] TTV is caused by the gravitational forces of all orbiting bodies acting upon each other. The probability of seeing a transit from Earth is low, however. The probability is given by the following equation.
<math>P_\text{transit}= (R_\text{star} + R_\text{planet})/a</math><ref name="Asher">{{Cite book|title=How do you find an exoplanet?|last=Asher|first=Johnson, John|date=29 December 2015|isbn=9780691156811|location=Princeton, New Jersey|oclc=908083548}}</ref>
Where Rstar and Rplanet is the radius of the star and planet, respectfully. The semi major axis length represented by a. Because of low probability large selections of the sky must be regularly observed in order to see a transit. [[Hot Jupiter]]s are more likely to be seen because of their larger radius and short semi major. In order to find earth size planets [[red dwarf]] stars are observed because of their small radius. Even though transiting has a low probability it has proven itself to be a good technique in discovering exoplanets.
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==== KELT ====
[[Kilodegree Extremely Little Telescope|KELT]] is a terrestrial telescope mission designed to search for transiting systems of planets of magnitude 8<M<10. It began operation in October 2004 in Winer Observatory and has a southern companion telescope added in 2009.<ref>{{Cite journal|last=Pepper|first=J.|last2=Pogge|first2=R.|last3=Depoy|first3=D. L.|last4=Marshall|first4=J. L.|last5=Stanek|first5=K.|last6=Stutz|first6=A.|last7=Trueblood|first7=M.|last8=Trueblood|first8=P.|date=1 July 2007|title=Early Results from the KELT Transit Survey|journal=Transiting Extrapolar Planets Workshop|volume=366|pages=27|bibcode=2007ASPC..366...27P|arxiv=astro-ph/0611947}}</ref> KELT North observes "26-degree wide strip of sky that is overhead from North America during the year", while KELT South observes single target areas of the size 26 by 26 degrees. Both telescopes dan detect and identify transit events as small as a 1% flux dip, which allows for detection of planetary systems similar to those in our solar system.<ref>{{Cite web|url=http://www.astronomy.ohio-state.edu/keltnorth/Method.html|title=KELT-North: Method|website=www.astronomy.ohio-state.edu|access-date=2018-12-16}}</ref><ref>{{Cite journal|last=Stassun|first=Keivan|last2=James|first2=David|last3=Siverd|first3=Robert|last4=Kuhn|first4=Rudolf B.|last5=Pepper|first5=Joshua|date=7 March 2012|title=The KELT-South Telescope|journal=Publications of the Astronomical Society of the Pacific|language=en|volume=124|issue=913|pages=230|doi=10.1086/665044|issn=1538-3873|arxiv=1202.1826|bibcode=2012PASP..124..230P}}</ref>
==== Kepler / K2 ====
The [[Kepler (spacecraft)|Kepler]] satellite served the Kepler mission between 7 March 2009 and 11 May 2013, where it observed one part of the sky in search of transiting planets within a 115 square degrees of the sky around the [[Cygnus (constellation)|Cygnus]], [[Lyra]], and [[Draco (constellation)|Draco]] constellations.<ref>{{Cite web|url=http://www.nasa.gov/mission_pages/kepler/overview/index.html|title=Mission overview|last=Johnson|first=Michele|date=13 April 2015|website=NASA|access-date=2018-12-16}}</ref> After that, the satellite continued operating until 15 November 2018, this time changing its field along the ecliptic to a new area roughly every 75 days due to reaction wheel failure.<ref>{{Cite journal|last=Fortney|first=Jonathan J.|last2=Twicken|first2=J. D.|last3=Smith|first3=Marcie|last4=Najita|first4=Joan R.|last5=Miglio|first5=Andrea|last6=Marcy|first6=Geoffrey W.|last7=Huber|first7=Daniel|last8=Cochran|first8=William D.|last9=Chaplin|first9=William J.|date=1 April 2014|title=The K2 Mission: Characterization and Early Results|journal=Publications of the Astronomical Society of the Pacific|language=en|volume=126|issue=938|pages=398|doi=10.1086/676406|issn=1538-3873|arxiv=1402.5163|bibcode=2014PASP..126..398H}}</ref>
==== TESS ====
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