Sam Hooke

Map of the Mullard Radio Astronomy Observatory (MRAO)

SITE 1.ADMINISTRATIONCambridge RoadWimpoleRoadHaslingfieldRoadBarton RoadLord's BridgeStationAMI Small ArrayCOASTAMI Large Array†Pulsar Array4C Array†Half-Mile Telescope (small) & †One-Mile Telescope (large)†One-MileTelescopeTrack continues 1km eastwardse-MERLIN†CLFST†CATUnknown?Unknown?†SKA†HERAUnknown?†SKAPrototypearrayPrototypeindividualPrototypeRyle ControlRoomOne-MileControlRoom(Previously site of †Ryle Telescope)(Track is shared)Name†NameLong BrookBourn Brook𝕳𝖊𝖞 𝕳𝖎𝖑𝖑𝕽𝖔𝖒𝖆𝖓𝕭𝖆𝖗𝖗𝖔𝖜NSITE 6.SEWAGE DISPOSALSITE 2.BOMB STORESSITE 4.F.F.D.4.1 Mile1 Kilometerhttps://sam.hooke.me/mraoJune 2024Mullard Radio AstronomyObservatory (MRAO)KeyFormer railwayTelescope railwayMain roadMRAO tarmac roadMRAO trackTelescope (static)Telescope (on track)Telescope (approx. area)Telescope (active)Telescope (inactive)MRAO (approx. area)

After visiting the Mullard Radio Astronomy Observatory (MRAO) in June 2024, I was surprised to find that there is no comprehensive map available online which displays the locations of all the telescopes. So, using photos and notes from my visit, combined with research online, I created the above map. The MRAO was formerly site of the Lord’s Bridge railway station, and during WWII the sidings served as a munitions storage facility. During my visit I found a map1 of these old facilities, so I have overlaid some of them (such as the location of the railway line), as they help explain the seemingly unusual layout.2

You can download a copy of the map below:

Telescopes §

Following is a full list of all the telescopes found at MRAO. As best as I can tell, at time of writing (January 2025) the Wikipedia page is not quite complete: it misses out the HERA prototype and SKA prototypes. There is also some other radio equipment I am uncertain about (labelled “Unknown?” on the map).

HERA (Hydrogen Epoch of Re-ionization Array) prototype §

Three dish shaped mesh receivers in a triangle formation on a grassy field.
The three prototype HERA receivers.

There are three prototype HERA receivers at MRAO, tessalated together in a triangle just west of the e-MERLIN receiver. Each dish is placed horizontally on the ground, with a receiver suspended above in the middle.

Papers §

SKA (Square Kilometer Array) prototype §

An antenna about the size and appearance of a Christmas tree.
An individual SKA prototype.

Each prototype SKA antenna at MRO is about the side of a Christmas tree, and similar in appearance. They are near the AMI Small Array. In one plot there is an individual SKA antenna, and behind a nearby hedge is a small array of SKA antennas.

CAT (Cosmic Anistrophy Telescope) §

Since CAT was decommissioned in 20003 there is not much left to see.

  • CAT official website (Internet Archive link because website has been down since April 2019)
  • Wikipedia
    • NOTE: The “Coordinates” field on Wikipedia has incorrectly marked the location of the CAT at MRAO! However, if you go to the category page, the map on the right has a hexagon with the CAT in the right place (but the marker is in the wrong place).
    • NOTE: The External link to “The CAT enclosure” is also wrong.

Cambridge MERLIN (enhanced Multi Element Remotely Linked Interferometer Network) §

A big parabolic receiver on a tower behind a line of trees.
Cambridge MERLIN.

With a 32m diameter, this is the biggest dish at MRAO. The Cambridge MERLIN radio telescope is part of the e-MERLIN network, which consists of seven radio telescopes situated around England.

Ryle Telescope §

The old Lord’s Bridge railway line ran almost exactly along an east-west parallel. For reasons I can’t pretend to explain, this alignment was ideal for the Ryle Telescope. It consisted of eight elements (dishes) arranged along the east-west parallel: four mounted on the 1.2km railway track, and four fixed at 1.2km intervals.

In 2006, the Ryle Telescope was repurposed for the AMI Large Array. So the Ryle Telescope itself no longer exists, however the same elements (dishes) are still present, but in a different configuration.

AMI (Arcminute Microkelvin Imager) §

Several big parabolic receivers, the nearby ones static, the distant ones mounted on a track.
AMI Large Array.
Seven medium sized parabolic receivers, all are static, encircled by an angled wall.
AMI Small Array.

The AMI consists of a pair of radio telescopes: the Small Array and Large Array. The Large Array consists of eight 12.8m diameter parabolic antennas (previously part of the Ryle Telescope).

COAST (Cambridge Optical Aperture Synthesis Telescope) §

A bunker covered in grass, with some white boxes and pipes on the field outside.
COAST.

Most of the COAST equipment is inside a bunker, so there is not much to see from outside.

CLFST (Cambridge Low Frequency Synthesis Telescope) §

Like the Ryle Telescope, the CLFST makes use of the east-west parallel from the old Lord’s Bridge railway line. It consisted of 60 yagi antennas. It ceased operating in 20004, but a group of antennas has been preserved which can still be seen today near the old Lord’s Bridge station house.

One-Mile Telescope §

An 18m wide parabolic receiver mounted on a very wide track.
The movable receiver of the One-Mile Telescope. The two fixed receivers are behind, out of view: one is directly behind, the other is half a mile away.

The One-Mile Telescope consists of two fixed receivers and one on a track.

Half-Mile Telescope §

Two slightly smaller parabolic receivers on a very wide track (exact diameter is unknown).
The two movable receivers of the Half-Mile Telescope. The two fixed receivers are further away at the other end of the track.

The Half-Mile Telescope consists of two fixed receivers and two on a track. It shares the same track as the One-Mile Telescope.

4C Array §

A row of 22 crescent moon shaped antennas, disappearing into the distance.
4C Array.

The 4C Array is a 450m long row of 20m wide antennas.5 It runs parallel to the track used by the One-Mile and Half-Mile Telescopes.

Interplanetary Scintillation Array §

The Interplanetary Scintillation Array, or Pulsar Array, consists of an array of 4096 dipole antennas spread across nine acres.

There are good pictures of it on this website.


  1. The old map of the munitions storage facility used to be classified information, but at some point since WWII was declassified. ↩︎

  2. For fun, I also included the nearby Hey Hill Roman Barrow↩︎

  3. According to this archive of the official CAT website from 26th April 2019, which says “The telescope was turned off and partly dismantled in 2000.” ↩︎

  4. According to this archive of the official CLFST website from 26th April 2019, which says “The 151-MHz telescope far exceeded its original projected lifetime and eventually ceased operating in 2000, but a group of aerials similar to those pictured here has been preserved at Lord’s Bridge.” ↩︎

  5. According to Wikipedia, there used to be “a second, moveable element (now mostly removed; some of it is still visible, beyond COAST)”. However, I am unsure where exactly this is. ↩︎