Editing Radio astronomy (section)

====Very-long-baseline interferometry====
{{main|Very-long-baseline interferometry}}

Beginning in the 1970s, improvements in the stability of radio telescope receivers permitted telescopes from all over the world (and even in Earth orbit) to be combined to perform [[very-long-baseline interferometry]]. Instead of physically connecting the antennas, data received at each antenna is paired with timing information, usually from a local [[atomic clock]], and then stored for later analysis on magnetic tape or hard disk. At that later time, the data is correlated with data from other antennas similarly recorded, to produce the resulting image. Using this method, it is possible to synthesise an antenna that is effectively the size of the Earth. The large distances between the telescopes enable very high angular resolutions to be achieved, much greater in fact than in any other field of astronomy. At the highest frequencies, synthesised beams less than 1 [[Minute of arc|milliarcsecond]] are possible.

The pre-eminent VLBI arrays operating today are the [[Very Long Baseline Array]] (with telescopes located across North America) and the [[European VLBI Network]] (telescopes in Europe, China, South Africa and Puerto Rico). Each array usually operates separately, but occasional projects are observed together producing increased sensitivity. This is referred to as Global VLBI. There are also a VLBI networks, operating in Australia and New Zealand called the LBA (Long Baseline Array),<ref>{{Cite web| url=http://www.atnf.csiro.au/vlbi/| title=VLBI at the ATNF| date=7 December 2016| access-date=16 June 2015| archive-date=1 May 2021| archive-url=https://web.archive.org/web/20210501051105/https://www.atnf.csiro.au/vlbi/| url-status=live}}</ref> and arrays in Japan, China and South Korea which observe together to form the East-Asian VLBI Network (EAVN).<ref>{{Cite web | url=http://www.astro.sci.yamaguchi-u.ac.jp/eavn/index.html | title=East Asia VLBI Network and Asia Pacific Telescope | access-date=2015-06-16 | archive-date=2021-04-28 | archive-url=https://web.archive.org/web/20210428080543/http://astro.sci.yamaguchi-u.ac.jp/eavn/index.html | url-status=live }}</ref>

Since its inception, recording data onto hard media was the only way to bring the data recorded at each telescope together for later correlation. However, the availability today of worldwide, high-bandwidth networks makes it possible to do VLBI in real time. This technique (referred to as e-VLBI) was originally pioneered in Japan, and more recently adopted in Australia and in Europe by the EVN (European VLBI Network) who perform an increasing number of scientific e-VLBI projects per year.<ref>{{Cite web |url=http://www.innovations-report.com/html/reports/physics_astronomy/report-25117.html |title=A technological breakthrough for radio astronomy – Astronomical observations via high-speed data link<!-- Bot generated title --> |date=26 January 2004 |access-date=2008-07-22 |archive-date=2008-12-03 |archive-url=https://web.archive.org/web/20081203145055/http://www.innovations-report.com/html/reports/physics_astronomy/report-25117.html |url-status=live }}</ref>