Editing Astrometry (section)

==Applications==
[[Image:orbit3.gif|thumb|right|200px|Diagram showing how a smaller object (such as an [[extrasolar planet]]) orbiting a larger object (such as a [[star]]) could produce changes in position and velocity of the latter as they orbit their common [[center of mass]] (red cross).]]
[[Image:Solar system barycenter.svg|thumb|right|200px|Motion of [[Barycentric coordinates (astronomy)|barycenter]] of solar system relative to the Sun]]
Apart from the fundamental function of providing [[astronomer]]s with a [[Frame of reference|reference frame]] to report their observations in, astrometry is also fundamental for fields like [[celestial mechanics]], [[stellar dynamics]] and [[galactic astronomy]]. In [[observational astronomy]], astrometric techniques help identify stellar objects by their unique motions. It is instrumental for [[time standard|keeping time]], in that [[Coordinated Universal Time|UTC]] is essentially the [[International Atomic Time|atomic time]] synchronized to [[Earth]]'s rotation by means of exact astronomical observations. Astrometry is an important step in the [[cosmic distance ladder]] because it establishes [[parallax]] distance estimates for stars in the [[Milky Way]].

Astrometry has also been used to support claims of [[Methods of detecting extrasolar planets#Astrometry|extrasolar planet detection]] by measuring the displacement the proposed planets cause in their parent star's apparent position on the sky, due to their mutual orbit around the center of mass of the system. Astrometry is more accurate in space missions that are not affected by the distorting effects of the Earth's atmosphere.<ref>Nature  462, 705 (2009) 8 December 2009 {{doi|10.1038/462705a}}</ref> NASA's planned [[Space Interferometry Mission]] ([[SIM PlanetQuest]]) (now cancelled) was to utilize astrometric techniques to detect [[terrestrial planet]]s orbiting 200 or so of the nearest [[Solar analog|solar-type stars]]. The European Space Agency's [[Gaia Mission]], launched in 2013, applies astrometric techniques in its stellar census. In addition to the detection of exoplanets,<ref>{{cite web| url = http://www.esa.int/esaSC/120377_index_0_m.html| title = ESA - Space Science - Gaia overview}}</ref> it can also be used to determine their mass.<ref>{{cite news|url=https://www.esa.int/Our_Activities/Space_Science/Gaia/Infant_exoplanet_weighed_by_Hipparcos_and_Gaia |title=Infant exoplanet weighed by Hipparcos and Gaia|date=20 August 2018|access-date=21 August 2018}}</ref>

Astrometric measurements are used by [[astrophysicist]]s to constrain certain models in [[celestial mechanics]]. By measuring the velocities of [[pulsar]]s, it is possible to put a limit on the [[asymmetry]] of [[supernova]] explosions. Also, astrometric results are used to determine the distribution of [[dark matter]] in the galaxy.

Astronomers use astrometric techniques for the tracking of [[near-Earth objects]]. Astrometry is responsible for the detection of many record-breaking Solar System objects. To find such objects astrometrically, astronomers use telescopes to survey the sky and large-area cameras to take pictures at various determined intervals. By studying these images, they can detect Solar System objects by their movements relative to the background stars, which remain fixed. Once a movement per unit time is observed, astronomers compensate for the parallax caused by Earth's motion during this time and the heliocentric distance to this object is calculated. Using this distance and other photographs, more information about the object, including its [[orbital elements]], can be obtained.<ref>{{cite web
 | first=Chadwick | last=Trujillo | author2=Rabinowitz, David
 | date=1 June 2007
 | url=http://www.gps.caltech.edu/%7Embrown/papers/ps/sedna.pdf
 | title=Discovery of a candidate inner Oort cloud planetoid
 | publisher=European Space Agency
 | access-date=2007-12-06 | archive-url= https://web.archive.org/web/20071026202421/http://www.gps.caltech.edu/~mbrown/papers/ps/sedna.pdf| archive-date= 26 October 2007 <!--DASHBot-->|url-status = live}}</ref> [[Asteroid impact avoidance]] is among the purposes.

[[Quaoar]] and [[Sedna (dwarf planet)|Sedna]] are two trans-Neptunian [[dwarf planet]]s discovered in this way by [[Michael E. Brown]] and others at Caltech using the [[Palomar Observatory]]'s [[Samuel Oschin telescope]] of {{convert|48|in|m}} and the Palomar-Quest large-area CCD camera. The ability of astronomers to track the positions and movements of such celestial bodies is crucial to the understanding of the Solar System and its interrelated past, present, and future with others in the Universe.<ref>{{cite web
 | first=Robert Roy | last=Britt
 | date=7 October 2002
 | url=http://www.space.com/scienceastronomy/quaoar_discovery_021007.html
 | title=Discovery: Largest Solar System Object Since Pluto
 | publisher=[[SPACE.com]] | access-date=2007-12-06
}}</ref><ref>{{cite web
 | first=Whitney | last=Clavin
 | date=15 May 2004
 | url=http://www.nasa.gov/vision/universe/solarsystem/planet_like_body.html
 | title=Planet-Like Body Discovered at Fringes of Our Solar System
 | publisher=[[NASA]] | access-date=2007-12-06 | archive-url= https://web.archive.org/web/20071130032242/http://www.nasa.gov/vision/universe/solarsystem/planet_like_body.html| archive-date= 30 November 2007 <!--DASHBot-->|url-status = live}}</ref>