Editing Astrophysics (section)

{{Short description|Subfield of astronomy}}
{{for|the academic journal|Astrophysics (journal)}}
[[Image:NIEdot362.jpg|thumb|Early 1900s comparison of elemental, solar, and stellar spectra]]
{{TopicTOC-Physics}}

'''Astrophysics''' is a science that employs the methods and principles of [[physics]] and [[chemistry]] in the study of [[astronomical object]]s and phenomena.<ref>{{cite book |title=Astrophysics in a Nutshell |first=Dan |last=Maoz |year= 2016 |publisher=Princeton University Press |pages=272 |isbn=978-1400881178 |url=https://books.google.com/books?id=bmBeCwAAQBAJ&pg=PA1}}</ref><ref>{{cite web | title=astrophysics | publisher=Merriam-Webster, Incorporated | url=http://www.merriam-webster.com/dictionary/astrophysics | access-date=2011-05-22 | archive-url= https://web.archive.org/web/20110610085146/http://www.merriam-webster.com/dictionary/astrophysics| archive-date= 10 June 2011 | url-status= live}}</ref> As one of  the founders of the discipline, [[James Edward Keeler|James Keeler]], said, astrophysics "seeks to ascertain the nature of the heavenly bodies, rather than their positions or motions in space—''what'' they are, rather than ''where'' they are",<ref>{{Citation | last = Keeler | first = James E. | author-link = James E. Keeler | title = The Importance of Astrophysical Research and the Relation of Astrophysics to the Other Physical Sciences | journal = The Astrophysical Journal | volume = 6 | issue = 4 | pages = 271–288 | date = November 1897 | bibcode = 1897ApJ.....6..271K |doi = 10.1086/140401 | pmid = 17796068 | doi-access = free }}</ref> which is studied in [[celestial mechanics]].

Among the subjects studied are the [[Sun]] ([[solar physics]]), other [[star]]s, [[galaxy|galaxies]], [[extrasolar planet]]s, the [[interstellar medium]], and the [[cosmic microwave background]].<ref name="nasa.gov">{{cite web|url=https://science.nasa.gov/astrophysics/focus-areas/|title=Focus Areas – NASA Science|work=nasa.gov|access-date=2017-07-12|archive-date=2017-05-16|archive-url=https://web.archive.org/web/20170516154030/https://science.nasa.gov/astrophysics/focus-areas|url-status=dead}}</ref><ref>{{cite encyclopedia|url=https://www.britannica.com/EBchecked/topic/40047/astronomy|title=astronomy|encyclopedia=Encyclopædia Britannica|date=29 May 2023 }}</ref> Emissions from these objects are examined across all parts of the [[electromagnetic spectrum]], and the properties examined include [[luminosity]], [[density]], [[temperature]], and [[chemistry|chemical]] composition. Because astrophysics is a very broad subject, ''astrophysicists'' apply concepts and methods from many disciplines of physics, including [[classical mechanics]], [[electromagnetism]], [[statistical mechanics]], [[thermodynamics]], [[quantum mechanics]], [[theory of relativity|relativity]], [[nuclear physics|nuclear]] and [[particle physics]], and [[atomic, molecular, and optical physics|atomic and molecular physics]].

In practice, modern astronomical research often involves substantial work in the realms of [[Theoretical physics|theoretical]] and observational physics. Some areas of study for astrophysicists include the properties of [[dark matter]], [[dark energy]], [[black holes]], and other [[celestial bodies]]; and the [[Cosmogony|origin]] and [[ultimate fate of the universe]].<ref name="nasa.gov"/> Topics also studied by theoretical astrophysicists include [[Formation and evolution of the Solar System|Solar System formation and evolution]]; [[stellar dynamics]] and [[Stellar evolution|evolution]]; [[galaxy formation and evolution]]; [[magnetohydrodynamics]]; [[large-scale structure of the universe|large-scale structure]] of [[matter]] in the universe; origin of [[cosmic ray]]s; [[general relativity]], [[special relativity]], and [[quantum cosmology|quantum]] and [[physical cosmology]] (the physical study of the largest-scale structures of the universe), including [[string theory|string]] cosmology and [[astroparticle physics]].