Editing Astronomy (section)

=== Astrometry and celestial mechanics ===
{{Main|Astrometry|Celestial mechanics}}
[[File:EmissionNebula NGC6357.jpg|thumb|Star cluster [[Pismis 24]] with a nebula]]
One of the oldest fields in astronomy, and in all of science, is the measurement of the positions of celestial objects. Historically, accurate knowledge of the positions of the Sun, Moon, planets and stars has been essential in [[celestial navigation]] (the use of celestial objects to guide navigation) and in the making of [[calendar]]s.<ref name=":0">{{Cite book |last=Fraknoi |first=Andrew |url=https://openstax.org/details/books/astronomy-2e |title=Astronomy 2e |date=2022 |display-authors=etal |publisher=OpenStax |isbn=978-1-951693-50-3 |edition=2e |oclc=1322188620 |access-date=16 March 2023 |archive-date=23 February 2023 |archive-url=https://web.archive.org/web/20230223211041/https://openstax.org/details/books/astronomy-2e |url-status=live }}</ref>{{rp|39}}

Careful measurement of the positions of the planets has led to a solid understanding of gravitational [[Perturbation theory|perturbations]], and an ability to determine past and future positions of the planets with great accuracy, a field known as [[celestial mechanics]]. More recently the tracking of [[near-Earth object]]s will allow for predictions of close encounters or potential collisions of the Earth with those objects.<ref>{{cite web|last = Calvert|first = James B.|date = 28 March 2003|url = http://www.du.edu/~jcalvert/phys/orbits.htm|title = Celestial Mechanics|publisher = University of Denver|access-date = 21 August 2006|archive-url = https://web.archive.org/web/20060907120741/http://www.du.edu/~jcalvert/phys/orbits.htm|archive-date = 7 September 2006}}</ref>

The measurement of [[stellar parallax]] of nearby stars provides a fundamental baseline in the [[cosmic distance ladder]] that is used to measure the scale of the Universe. Parallax measurements of nearby stars provide an absolute baseline for the properties of more distant stars, as their properties can be compared. Measurements of the [[radial velocity]] and [[proper motion]] of stars allow astronomers to plot the movement of these systems through the Milky Way galaxy. Astrometric results are the basis used to calculate the distribution of speculated [[dark matter]] in the galaxy.<ref>{{cite web|url=http://www.astro.virginia.edu/~rjp0i/museum/engines.html|title=Hall of Precision Astrometry|publisher=[[University of Virginia]] Department of Astronomy|access-date=17 November 2016|archive-url=https://web.archive.org/web/20060826104509/http://www.astro.virginia.edu/~rjp0i/museum/engines.html|archive-date=26 August 2006 }}</ref>

During the 1990s, the measurement of the [[stellar wobble]] of nearby stars was [[Methods of detecting extrasolar planets#Astrometry|used to detect]] large [[extrasolar planet]]s orbiting those stars.<ref name="Wolszczan">{{cite journal| author=Wolszczan, A.| author2=Frail, D. A.| title=A planetary system around the millisecond pulsar PSR1257+12| journal=Nature| date=1992| volume=355| issue=6356|pages=145–47| doi= 10.1038/355145a0| bibcode=1992Natur.355..145W| s2cid=4260368}}</ref>