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{{Other uses|Merlin (disambiguation)}}
{{Use dmy dates|date=April 2022}}
{{Infobox Observatory|location=[[England]]}}

The '''Multi-Element Radio Linked Interferometer Network''' ('''MERLIN''') is an [[interferometer]] array of [[radio telescope]]s spread across [[England]]. The array is run from [[Jodrell Bank Observatory]] in [[Cheshire]] by the [[University of Manchester]] on behalf of [[UK Research and Innovation]].<ref>{{cite journal | last=Davies | first=J. G. |display-authors=etal | date=1980 | doi= 10.1038/288064a0 | title=The Jodrell Bank radio-linked interferometer network  | volume=288 | pages=64–66 | journal=[[Nature (journal)|Nature]]|bibcode = 1980Natur.288...64D | issue=5786| s2cid=4338231 }}</ref><ref>{{cite book | first = Bernard | last = Lovell | author-link = Bernard Lovell | title = The Jodrell Bank Telescopes | publisher=[[Oxford University Press]] |date=1985 | isbn = 0-19-858178-5}}</ref><ref>{{cite book | first=Lovell | last=Bernard | author-link=Bernard Lovell | date=1990 | title=Astronomer by Chance | publisher=Macmillan | location=London | isbn=0-333-55195-8}}</ref>

The array consists of up to seven [[radio telescope]]s and includes the [[Lovell Telescope]] at Jodrell Bank, [[Mark II (radio telescope)|Mark II]], Cambridge, [[Defford]] in [[Worcestershire]], [[Knockin]] in [[Shropshire]], and [[Darnhall]] and [[Pickmere]] (previously known as Tabley) in [[Cheshire]].<ref>{{Cite journal|last1=Bahcall|first1=J. N.|last2=Kirhakos|first2=S.|last3=Schneider|first3=D. P.|last4=Davis|first4=R. J.|last5=Muxlow|first5=T. W. B.|last6=Garrington|first6=S. T.|last7=Conway|first7=R. G.|last8=Unwin|first8=S. C.|date=1995|title=Hubble Space Telescope and MERLIN Observations of the Jet in 3C 273|journal=The Astrophysical Journal Letters|language=en|volume=452|issue=2|pages=L91|doi=10.1086/309717|issn=1538-4357|arxiv = astro-ph/9509028 |bibcode = 1995ApJ...452L..91B |s2cid=118401963}}</ref><ref>{{Cite journal|last1=Akujor|first1=Chidi E.|last2=Spencer|first2=R. E.|last3=Zhang|first3=F. J.|last4=Davis|first4=R. J.|last5=Browne|first5=I. W. A.|last6=Fanti|first6=C.|date=1991|title=MERLIN observations of steep-spectrum radio sources at 6 cm|journal=Monthly Notices of the Royal Astronomical Society|volume=250|issue=1|pages=215–224|doi=10.1093/mnras/250.1.215|issn=0035-8711|bibcode = 1991MNRAS.250..215A |doi-access=free}}</ref> The longest baseline is therefore 217&nbsp;km and MERLIN can operate at [[Frequency|frequencies]] between 151&nbsp;[[Hertz|MHz]] and 24&nbsp;[[Hertz|GHz]]. At a [[wavelength]] of 6&nbsp;cm (5&nbsp;GHz frequency), MERLIN has a resolution of 40 [[arcsecond|milliarcseconds]] which is comparable to that of the [[Hubble Space Telescope|HST]] at optical wavelengths.{{Citation needed|date=June 2007}}

Some of the telescopes are occasionally used for [[European VLBI Network]] (EVN) and [[Very Long Baseline Interferometry]] (VLBI) observations in order to create an [[interferometer]] with even larger baselines, providing images with much greater [[angular resolution]].

==MTLRI==
[[File:Knockin Radio Telescope.jpg|thumb|right|200px|The radio telescope at Knockin]]
In 1973, Henry Proctor Palmer made the suggestion of extending the interferometer links already in place at Jodrell Bank at the time, which started the planning of the telescope array.<ref name="jbtelescopes_184">Lovell, ''Jodrell Bank Telescopes'', p. 184<br />Lovell, ''Astronomer by Chance'', p. 312</ref><ref name="1980Davies">Davies et al. (1980)</ref> Construction started in 1975.<ref name="1980Davies" /> The system was originally officially called MTRLI (Multi-Telescope Radio Linked Interferometer), but was commonly referred to by the simpler name of MERLIN. It originally consisted of either the 76m [[Lovell Telescope]] or the 25m [[Mark II (radio telescope)|Mark II]], along with the 25m [[Mark III (radio telescope)|Mark III]] at Wardle, the 85&nbsp;ft at Defford and a new telescope at Knockin. This
new telescope was made by [[E-Systems]] and was constructed based on the design for the telescopes in the [[Very Large Array]], which was being constructed at the same time also by E-Systems.<ref name="jbo_mtrli">{{cite web | url=http://www.jb.man.ac.uk/public/story/mtrli.html | title=JBO – MTRLI | access-date=2007-06-10}}</ref><ref name="jbtelescopes_185">Lovell, ''Jodrell Bank Telescopes'', p. 185</ref>

The construction of the new telescope, the installation of microwave communication links and the construction of the correlator were jointly called "Phase 1" of the MERLIN project, the funding for which was approved on 30 May 1975.<ref name="jbtelescopes_191">Lovell, ''Jodrell Bank Telescopes'', p. 191</ref> The construction of the new telescope started on 9 July 1976, and was completed by 8 October 1976. The telescope was first controlled remotely from Jodrell in January 1977.<ref name="jbtelescopes_201">Lovell, ''Jodrell Bank Telescopes'', p. 201</ref> The microwave links were installed in May 1978.<ref name="jbtelescopes_203">Lovell, ''Jodrell Bank Telescopes'', p. 203</ref> The first observations using the system – measurements of 30 distant radio sources – were taken in January and February 1980.<ref name="jbtelescopes_204">Lovell, ''Jodrell Bank Telescopes'', p. 204</ref> The final cost of phase 1 of the system was £2,179,000 (1976).<ref name="jbtelescopes_204" />

Two additional telescopes were added in Phase 2 of the project, along with their radio links to Jodrell Bank. While it was originally proposed that one of the telescopes would be sited at Jodrell Bank and the other at Darnhall, the pair were finally sited at Pickmere (also known as Tabley) and Darnhall. The two telescopes were the same as that at Knockin. Construction on both telescopes started on 9 April 1979, and was completed by 31 October 1979. The Pickmere telescope was connected into MTRLI for the first time on 20 July 1980, followed by the Darnhall telescope on 16 December 1980. The second phase was formally completed on the 31 December 1981, and had cost £3,142,210.<ref name="jbtelescopes_c20">Lovell, ''Jodrell Bank Telescopes'', Chapter 20 (pp. 208–215)</ref>

The longest baseline of MTRLI was 134&nbsp;km, between Pickmere and Defford.<ref name="jbo_mtrli" /> The first map produced by the array was published on 6 November 1980.<ref name="1980Davies" /> In the first 2 years of operation (1980–1982), the array was used to observe at frequencies of 408&nbsp;MHz (with a resolving power of 1&nbsp;[[arcsecond]]), 1666&nbsp;MHz (0.25&nbsp;arcsecond) and 5&nbsp;GHz (0.08&nbsp;arcsecond).<ref name="jbtelescopes_220">Lovell, ''Jodrell Bank Telescopes'', p. 220</ref>

When the [[Mark II (radio telescope)|Mark II]]'s surface was replaced in 1987, it could be used along with the three E-systems telescopes on the 22&nbsp;GHz frequency, expanding MTRLI at that frequency.<ref name="jbo_mtrli" /> One of the 18&nbsp;m dishes of the [[One-Mile Telescope]] was temporarily used in MTRLI from 1987 until autumn 1990, which greatly improved its resolution.<ref name="jbo_onemile">{{cite web | url=http://www.merlin.ac.uk/about/layman/32m.html | title=MERLIN: The 32-metre Telescope | publisher=Merlin.ac.uk | access-date=2010-08-17}}</ref>
[[File:cmglee Cambridge MRAO MERLIN.jpg|thumb|right|200px|The Cambridge antenna in June 2014]]
MTRLI was renamed to MERLIN in the early 1990s, and shortly afterwards the addition of the purpose-built 32&nbsp;m Cambridge antenna in 1991 increased both the sensitivity and [[angular resolution]] of the array. The array also had a new correlator and new, cooled receivers, and some of the microwave links between the telescopes were improved so that the array could observe both hands of polarization.<ref name="jbo_merlin">{{cite web | url=http://www.jb.man.ac.uk/public/story/merlin.html | title=JBO – MERLIN | access-date=2007-06-10}}</ref>

Since 1996, carousels for the different receivers on each of the E-systems telescopes and the [[Mark II (radio telescope)|Mark II]] telescope were installed (the Cambridge telescope already had such a system installed), providing frequency agility. In 1997 and 1998, dual-frequency (5 and 22&nbsp;GHz) observations were made with the array for the first time.<ref name="jbo_merlin"/>

There are plans to construct a telescope in [[Ireland]] that would be added to the array.<ref name="bbc_irish_merlin">{{cite news | url=http://news.bbc.co.uk/1/hi/sci/tech/953415.stm | title=Irish giant could get new partner | publisher=[[BBC News]] | date=2 October 2000 | access-date=2007-04-06 }}<br />{{cite web | url=http://www.arti.ie/ | title=A Radio Telescope for Ireland | access-date=2007-04-06 | archive-url=https://web.archive.org/web/20070407003022/http://www.arti.ie/ | archive-date=2007-04-07 }}</ref>
{| class="wikitable" style="float: left; font-size: 90%"
|-
! colspan=2 | Original MTRLI telescopes
|-
! '''Name''' !! [[Geographic coordinate system|Coordinates]]<br />(links to map & photo sources)
|-
| [[Lovell Telescope]] || {{coord|53|14|10.50|N|02|18|25.74|W|name=Lovell Telescope}}
|-
| [[Mark II (radio telescope)|Mark II]] || {{coord|53|13|51.62|N|02|18|34.16|W|name=Mark II}}
|-
| [[Mark III (radio telescope)|Mark III]] || {{coord|53|06|09.16|N|02|31|15.63|W|name=Mark III}}<ref>{{cite web | url=http://www.merlin.ac.uk/user_guide/OnlineMUG-ajh/newch0-node62.html | title=MERLIN user guide – 4.1 Location of Telescopes | access-date=2010-09-01}}</ref>
|-
| Defford || {{coord|52|05|27.61|N|02|08|09.62|W|name=Defford}}
|-
| Knockin || {{coord|52|47|23.9|N|02|59|44.9|W|name=Knockin}}
|-
| Pickmere || {{coord|53|17|18.4|N|02|26|38.4|W|name=Pickmere}}
|-
| Darnhall || {{coord|53|09|21.6|N|02|32|03.3|W|name=Darnhall}}
|}

{| class="wikitable" style="float: left; font-size: 90%"
|-
! colspan=2 | Current MERLIN telescopes
|-
! '''Name''' !! [[Geographic coordinate system|Coordinates]]<br />(links to map & photo sources)
|-
| [[Lovell Telescope]] || {{coord|53|14|10.50|N|02|18|25.74|W|name=Lovell Telescope}}
|-
| [[Mark II (radio telescope)|Mark II]] || {{coord|53|13|51.62|N|02|18|34.16|W|name=Mark II}}
|-
| Defford || {{coord|52|05|27.61|N|02|08|09.62|W|name=Defford}}
|-
| Knockin || {{coord|52|47|23.9|N|02|59|44.9|W|name=Knockin}}
|-
| Pickmere || {{coord|53|17|18.4|N|02|26|38.4|W|name=Pickmere}}
|-
| Darnhall || {{coord|53|09|21.6|N|02|32|03.3|W|name=Darnhall}}
|-
| Cambridge ([[Mullard Radio Astronomy Observatory|MRAO]]) || {{coord|52|10|1.2|N|0|2|13.4|E|name=Cambridge}}
|-
| [[Goonhilly]]<ref>{{cite web | url=https://www.goonhilly.org/antennas/ghy-1-arthur | title=GHY-1 ARTHUR | access-date=2019-12-12 | archive-date=12 December 2019 | archive-url=https://web.archive.org/web/20191212125020/https://www.goonhilly.org/antennas/ghy-1-arthur }}</ref> || {{coord|50|02|53|N|05|10|55|W|name=Arthur}}
|}
{{clear}}

==e-MERLIN==
MERLIN  used [[microwave]] links to send astronomical data back from the remote stations. These links had a limited bandwidth so much of the data was thrown away.  In order to increase the sensitivity of the telescope the links were replaced by [[optical fibre]] links with a [[Bandwidth (signal processing)|bandwidth]] of 4&nbsp;GHz, compared to the original limit of 30&nbsp;MHz, increasing the sensitivity of the array by a factor of around 30.  This vast increase in data meant that the old correlator was no longer able to cope, so a new correlator was constructed which is capable of processing over 200&nbsp;Gbit/s.<ref>{{cite web|url=https://www.bbc.co.uk/news/science-environment-11952890|title= 'Superscope' yields first glimpse of Double Quasar|publisher=[[BBC]]|date=2010-12-10}}</ref>

Another major development which is part of the upgrade is frequency flexibility — the ability to alter the observing band of the entire array in a matter of minutes using rotating carousels of receivers.  Some telescopes in the array already had this capability, while the rest required the visit of an engineer to change the receiver.  When e-MERLIN becomes operational{{update-inline|date=June 2024}} the telescope will be able to switch rapidly between 1.4, 5, 6 and 22&nbsp;GHz.  This is required in order to take advantage of optimum conditions for high frequency observations where atmospheric conditions can severely affect results.{{Citation needed|date=June 2007}}

Work started on the e-MERLIN upgrade in May 2004 and it was completed in 2009.<ref name=HealyOBrien2016>{{cite journal|last1=Healy|first1=F.|last2=O'Brien|first2=T. J.|author-link2=Timothy John O'Brien|last3=Beswick|first3=R.|title=eMERLIN imaging of γ-ray nova V959 Mon's surprising evolution|journal=Journal of Physics: Conference Series|volume=728|issue=4|year=2016|article-number=042002|issn=1742-6588|doi=10.1088/1742-6596/728/4/042002|bibcode=2016JPhCS.728d2002H|doi-access=free}}</ref><ref name="bbc_merlin">{{cite news | url=http://news.bbc.co.uk/1/hi/sci/tech/3749919.stm | title=Giant UK telescope gets upgrade | publisher=BBC News | date=26 May 2004 | access-date=2007-04-05}}</ref>

=== STFC's Programmatic Review 2007–08 ===

On 6 March 2008 the Science and Technology Facilities Council ([[Science and Technology Facilities Council|STFC]]) announced that the (e-MERLIN/[[Joint Institute for VLBI in Europe|JIVE]]) project was at risk because of a £80m shortfall in its budget. This was due to the initial recommendations of the Particle Physics, Astronomy and Nuclear Physics Science Committee (PPAN), that had listed the project as a "lower priority". Following concerns that PPAN's recommendations did not adequately represent the UK's astronomical priorities,<ref>{{cite news | url=https://www.timesonline.co.uk/tol/news/uk/science/article3532951.ece | work=The Times | location=London | title=Jodrell Bank to close because scientists voted for own plans | first=Lewis | last=Smith | date=12 March 2008 | access-date=12 May 2010 }}{{Dead link|date=July 2025 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> [[Science and Technology Facilities Council|STFC]] established a wider consultation review involving various advisory panels to re-priorities the [[Science and Technology Facilities Council|STFC]] program.<ref>{{cite web|url=http://www.stfc.ac.uk/STFCConsultation/comment.aspx?ci%3D1%26m%3D2 |title=STFC Consultation - Comment |access-date=2008-08-15 |archive-url=https://web.archive.org/web/20080802001758/http://www.stfc.ac.uk/STFCConsultation/comment.aspx?ci=1&m=2 |archive-date=2008-08-02 }}</ref> The Ground-Based Astronomy Consultation Panel then recommended e-MERLIN should be changed from the lowest band ("lower priority"), to the second highest, adding that "e-Merlin could be a world-leading facility well into the next decade" and "e-Merlin offered dramatic potential to both traditional UK radio astronomy users and importantly to a broader community".<ref>{{cite web|url=http://www.stfc.ac.uk/STFCConsultation/sources/GBARep.pdf |title=Archived copy |access-date=2008-08-15 |archive-url=https://web.archive.org/web/20090227193151/http://www.stfc.ac.uk/STFCConsultation/sources/GBARep.pdf |archive-date=2009-02-27 }}</ref>

On 8 July 2008 [[Science and Technology Facilities Council|STFC]] presented their final version of the programmatic review at a Town
Meeting at the Royal Society stating: "Given the strategic importance of e-MERLIN to the future of UK radio astronomy and to the highly ranked SKA project, we are working with the University of Manchester and other stakeholders to find a viable way in which e-MERLIN operations can be supported in the medium term on a shared cost basis. We have made provision for [[Science and Technology Facilities Council|STFC]] support of operations to be made available to facilitate such a solution."<ref>{{cite web|url=http://www.stfc.ac.uk/STFCConsultation/sources/PPANRep.pdf |title=Archived copy |access-date=2009-04-12 |archive-url=https://web.archive.org/web/20090227193148/http://www.stfc.ac.uk/STFCConsultation/sources/PPANRep.pdf |archive-date=2009-02-27 }}</ref>

== Scientific results ==
Among many other things, MERLIN has been used to observe:
* Radio-loud galaxies, for example [[Messier 87]].<ref name="jbtelescopes_220"/>
* Quasars, for example [[3C 418]].<ref name="jbtelescopes_221">Lovell, ''Jodrell Bank Telescopes'', p. 221</ref>
* Spectral line observations of [[Hydroxyl]] (OH) in interstellar gas clouds.<ref name="jbtelescopes_224">Lovell, ''Jodrell Bank Telescopes'', p. 224</ref>
The telescope can also be used for highly precise [[astrometry]].<ref name="jbtelescopes_226">Lovell, ''Jodrell Bank Telescopes'', p. 226</ref> In 1998, MERLIN in conjunction with the [[Hubble Space Telescope]] discovered the first [[Einstein ring]].<ref>{{cite web | url=http://www.merlin.ac.uk//press/PR9801/press.html | title=A Bull's Eye for MERLIN and the Hubble | access-date=2007-06-10}}</ref> The telescope has also been used in combination with the VLA to carry out a [[Weak gravitational lensing|weak lensing analysis]].<ref>{{cite journal | title=Radio weak gravitational lensing with VLA and MERLIN | bibcode=2010MNRAS.401.2572P | last1=Patel | first1=P. | last2=Bacon | first2=D. J. | last3=Beswick | first3=R. J. | last4=Muxlow | first4=T. W. B. | last5=Hoyle | first5=B. | volume=401 | date=2010 | page=2572 | journal=[[Monthly Notices of the Royal Astronomical Society]] | doi=10.1111/j.1365-2966.2009.15836.x | issue=4| doi-access=free |arxiv = 0907.5156 | s2cid=55876431 }}</ref>

== References ==
{{Reflist|35em}}

{{commons category|MERLIN}}

{{geoGroup}}

{{Radio-astronomy}}
{{Jodrell Bank Observatory}}

{{DEFAULTSORT:Merlin}}
[[Category:Jodrell Bank Observatory]]
[[Category:Astronomical observatories in England]]
[[Category:Radio telescopes]]
[[Category:Interferometric telescopes]]
[[Category:Science and Technology Facilities Council]]