Editing Astronomy (section)

=== Deep space astronomy ===
[[File:Andromeda_Nebula_-_Isaac_Roberts,_29_December_1888 (cropped).jpg|thumb|The earliest known photograph of the [[Andromeda Galaxy|Great Andromeda "Nebula"]], by [[Isaac Roberts]] from 29 December 1888. With the calculation of its distance in 1923 [[intergalactic space]] was proven, allowing the calculation of the age and expanse of the [[Universe]].]]
The existence of the Earth's galaxy, the [[Milky Way]], as its own group of stars was only proven in the 20th century, along with the existence of "external" galaxies. The observed recession of those galaxies led to the discovery of the expansion of the [[Universe]].<ref name=Belkora2003>{{cite book|author=Belkora, Leila|title=Minding the heavens: the story of our discovery of the Milky Way|isbn=978-0-7503-0730-7|url=https://books.google.com/books?id=qBM-wez94WwC|publisher=[[CRC Press]]|date=2003|pages=1–14|access-date=26 August 2020|archive-date=27 October 2020|archive-url=https://web.archive.org/web/20201027093857/https://books.google.com/books?id=qBM-wez94WwC|url-status=live}}</ref> In 1919, when the [[Hooker Telescope]] was completed, the prevailing view was that the universe consisted entirely of the Milky Way Galaxy. Using the Hooker Telescope, [[Edwin Hubble]] identified [[Cepheid variable]]s in several spiral nebulae and in 1922–1923 proved conclusively that [[Andromeda Galaxy|Andromeda Nebula]] and [[Triangulum Nebula|Triangulum]] among others, were entire galaxies outside our own, thus proving that the universe consists of a multitude of galaxies.<ref name="SharovNovikov1993">{{cite book|last1=Sharov|first1=Aleksandr Sergeevich|last2=Novikov|first2=Igor Dmitrievich|title=Edwin Hubble, the discoverer of the big bang universe|url=https://books.google.com/books?id=ttEwkEdPc70C&pg=PA34|access-date=December 31, 2011|date=1993|publisher=Cambridge University Press|isbn=978-0-521-41617-7|page=34|archive-date=June 23, 2013|archive-url=https://web.archive.org/web/20130623075250/http://books.google.com/books?id=ttEwkEdPc70C&pg=PA34|url-status=live}}</ref> With this Hubble formulated the [[Hubble constant]], which allowed for the first time a calculation of the age of the Universe and size of the Observable Universe, which became increasingly precise with better meassurements, starting at 2 billion years and 280 million light-years, until 2006 when data of the [[Hubble Space Telescope]] allowed a very accurate calculation of the age of the Universe and size of the Observable Universe.<ref name="p537">{{cite web | title=Cosmic Times | website=Imagine the Universe! | date=December 8, 2017 | url=https://imagine.gsfc.nasa.gov/educators/programs/cosmictimes/educators/guide/age_size.html | access-date=October 31, 2024}}</ref>

[[File:Black hole - Messier 87 crop max res.jpg|thumb|First ever direct image of a ([[supermassive black hole|supermassive]]) [[black hole]], taken 2019 [[Radio astronomy|in radio wavelength]], located at the core of [[Messier 87]].]]

Theoretical astronomy led to speculations on the existence of objects such as [[black hole]]s and [[neutron star]]s, which have been used to explain such observed phenomena as [[quasar]]s, [[pulsar]]s, [[blazar]]s, and [[radio galaxy|radio galaxies]]. [[Physical cosmology]] made huge advances during the 20th century. In the early 1900s the model of the [[Big Bang]] theory was formulated, heavily evidenced by [[cosmic microwave background radiation]], [[Hubble's law]], and the [[Big Bang nucleosynthesis|cosmological abundances of elements]]. [[Space telescope]]s have enabled measurements in parts of the electromagnetic spectrum normally blocked or blurred by the atmosphere.<ref>{{cite book | chapter=Beating the atmosphere | first=Ian S. | last=McLean | title=Electronic Imaging in Astronomy | series=Springer Praxis Books | date=2008 | isbn=978-3-540-76582-0 | pages=39–75 | publisher=Springer | location=Berlin, Heidelberg | doi=10.1007/978-3-540-76583-7_2 }}</ref> In February 2016, it was revealed that the [[LIGO]] project had [[first observation of gravitational waves|detected evidence]] of [[gravitational waves]] in the previous September.<ref name="Discovery 2016">{{cite journal |title=Einstein's gravitational waves found at last |journal=Nature News |url=http://www.nature.com/news/einstein-s-gravitational-waves-found-at-last-1.19361 |date=11 February 2016 |last1=Castelvecchi |first1=Davide |last2=Witze |first2=Witze |doi=10.1038/nature.2016.19361 |s2cid=182916902 |access-date=11 February 2016 |archive-date=12 February 2016 |archive-url=https://web.archive.org/web/20160212082216/http://www.nature.com/news/einstein-s-gravitational-waves-found-at-last-1.19361 |url-status=live }}</ref><ref name='Abbot'>{{cite journal |title=Observation of Gravitational Waves from a Binary Black Hole Merger| author=B.P. Abbott |collaboration=LIGO Scientific Collaboration and Virgo Collaboration| journal=Physical Review Letters| year=2016| volume=116|issue=6| pages=061102| doi=10.1103/PhysRevLett.116.061102| pmid=26918975| bibcode=2016PhRvL.116f1102A|arxiv = 1602.03837 | s2cid=124959784}}</ref>