Editing Very-long-baseline interferometry (section)

== VLBI arrays ==
There are several VLBI arrays located in [[Europe]], [[Canada]], the [[United States]], [[Chile]], [[Russia]], [[China]], [[South Korea]], [[Japan]], [[Mexico]], [[Australia]] and [[Thailand]]. The most sensitive VLBI array in the world is the [[European VLBI Network]] (EVN). This is a part-time array that brings together the largest European radiotelescopes and some others outside of Europe for typically weeklong sessions, with the data being processed at the [[Joint Institute for VLBI in Europe]] (JIVE). The [[Very Long Baseline Array]] (VLBA), which uses ten dedicated, 25-meter telescopes spanning 5351 miles across the United States, is the largest VLBI array that operates all year round as both an astronomical and [[geodesy]] instrument.<ref>{{cite web|url=http://www.nrao.edu/index.php/about/facilities/vlba |title=Very Long Baseline Array (VLBA) |work=National Radio Astronomy Observatory |access-date=May 30, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120611150939/https://www.nrao.edu/index.php/about/facilities/vlba |archive-date=June 11, 2012 }}</ref> The combination of the EVN and VLBA is known as [[Global VLBI]]. When one or both of these arrays are combined with space-based VLBI antennas such as [[HALCA]] or [[Spektr-R]], the resolution obtained is higher than any other astronomical instrument, capable of imaging the sky with a level of detail measured in [[microarcsecond]]s. VLBI generally benefits from the longer baselines afforded by international collaboration, with a notable early example in 1976, when radio telescopes in the United States, USSR and [[Australia]] were linked to observe [[hydroxyl radical|hydroxyl]]-[[astrophysical maser|maser]] sources.<ref>First Global Radio Telescope, Sov. Astron., Oct 1976</ref> This technique is currently being used by the [[Event Horizon Telescope]], whose goal is to observe the [[supermassive black holes]] at the centers of the [[Milky Way Galaxy]] and [[Messier 87]].<ref name="APJL-20190410">{{cite journal |author=The Event Horizon Telescope Collaboration |title=First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole |date=April 10, 2019 |journal=[[The Astrophysical Journal Letters]] |volume= 875|pages=L1 |number=1 |doi=10.3847/2041-8213/ab0ec7 |arxiv=1906.11238 |doi-access=free |bibcode=2019ApJ...875L...1E }}</ref><ref name="BoumanJohnson2016">{{cite book|last1=Bouman|first1=Katherine L.|title=2016 IEEE Conference on Computer Vision and Pattern Recognition (CVPR)|author-link1=Katie Bouman|last2=Johnson|first2=Michael D.|last3=Zoran|first3=Daniel|last4=Fish|first4=Vincent L.|last5=Doeleman|first5=Sheperd S.|last6=Freeman|first6=William T.|chapter=Computational Imaging for VLBI Image Reconstruction|year=2016|pages=913–922|doi=10.1109/CVPR.2016.105 |hdl=1721.1/103077|arxiv=1512.01413|isbn=978-1-4673-8851-1|s2cid=9085016}}</ref><ref>{{cite news |last=Webb |first=Jonathan |url=https://www.bbc.com/news/science-environment-35258378 |title=Event horizon snapshot due in 2017 |publisher=[[BBC News]] |date=8 January 2016 |access-date=2017-10-22 |website=bbc.com}}</ref>

[[File:Malargue-VLBI distances.png|thumb|left|upright=1.5|Distance to Malargue station from the other stations of the NASA VLBI network]]
[[NASA]]s [[Deep Space Network]] uses its larger antennas (normally used for spacecraft communication) for VLBI, in order to construct radio reference frames for the purpose of spacecraft navigation. The inclusion of the ESA station at Malargue, Argentina, adds baselines that allow much better coverage of the southern hemisphere.<ref>{{cite conference |title=The X/Ka Celestial Reference Frame: towards a GAIA frame tie |author=Garcia-Mir, C and Sotuela, I and Jacobs, CS and Clark, JE and Naudet, CJ and White, LA and Madde, R and Mercolino, M and Pazos, D and Bourda, G.
  |conference=12th European VLBI Network Symposium and Users Meeting (EVN 2014)
  |volume=3
  |year=2014 |url=https://pos.sissa.it/230/033/pdf}}</ref>