La Palma

CTAO's site in the northern hemisphere

>> Visit our Flickr page for more photos and renderings of the La Palma site. <<

Northern Hemisphere Array

CTAO’s northern hemisphere or CTAO-North site is located on the existing site of the Instituto de Astrofisica de Canarias’ (IAC’s) Observatorio del Roque de los Muchachos in Villa de Garafia on the island of La Palma, the fifth largest island in the Canary Islands. At 2,200 metres in altitude and nestled on a plateau below the rim of an extinct volcanic crater, the site currently hosts an operating gamma-ray observatory, the Major Atmospheric Gamma Ray Imaging Cherenkov (MAGIC) telescopes, as well as a wide variety of optical telescopes of various sizes.

See more pictures on our Flickr page.

Array Coordinates:

Longitude: 17º 53′ 31.218″ West
Latitude: 28º 45′ 43.7904″ North

Proposed Array Layout

While the southern hemisphere array will span over the medium and high CTAO’s energy range, optimized for gamma-ray energies between 150 GeV to 300 TeV, the northern hemisphere array will focus on the low- and mid-energy ranges from 20 GeV to 5 TeV, which implies the specialization of the northern array in extragalactic physics. For this reason, the northern hemisphere site will not host any Small-Sized Telescopes, which are tuned to capture the highest-energy gamma rays. For the first construction phase, the approved Alpha Configuration, the plan is for the site to host four Large-Sized Telescopes to capture the low-energy sensitivity of CTAO and nine Medium-Sized Telescopes to cover CTAO’s core energy range.


The proposed layout of the CTAO Northern array, which defines the geographical positions of the elements (telescopes, calibration systems and atmospheric characterization devices), is contingent on the approval of the construction permits released by the local authorities on La Palma, which is being managed by the IAC on behalf of the CTAO.


Large-Sized Telescope Prototype Live Webcam

A Large-Sized Telescope prototype is being commissioned on the La Palma site. Watch live:

Announcements and Construction Updates

Originally published (in English and Spanish) in March 2020 issue of CTA Newsletter.


The CTAO and the Instituto de Astrofísica de Canarias’ (IAC) are pressing forward with preparations for the construction of the CTA-North site array, which is located on the existing site of the Observatorio del Roque de los Muchachos (ORM) in Villa de Garafía on the island of La Palma, Spain. Work on the detailed design for the four Large-Size Telescopes (LSTs) and the operation building continues, and the permit process is ongoing, including a more detailed evaluation of the array’s projected environmental impact, as requested by the local municipality. The expectation is to begin construction this year.


In December 2019, a review panel of five external and two internal representatives completed the first CTA-North system definition review. A package of 33 documents was provided to the panel, identifying all the major systems (e.g. requirement specifications, product breakdown structure, operations concept) and sub-systems (e.g. infrastructure, information and communication, LST and Medium-Sized Telescope requirements, array control and data acquisition) required for the operation of the array. Since the review, the actions are being addressed and the documents are expected to be completed and released in March 2020.


On site, the LST prototype (LST-1) and ORM weathered their worst Calima (a hot eastern wind from Africa) in recorded history during the last week of February. Although the wind gusts reached 157 km, no major damage was reported, and the assessment of the effects is ongoing. CTAO Site Manager, Paolo Calisse, recently began taking shifts at the LST-1 to familiarize himself with the instrument and contribute to the commissioning. A Critical Design Review (CDR) for the LST-1 was held in October 2019, where both minor and major actions to be addressed by both the LST and CTAO teams were identified in order to close out the CDR. The next step, which is currently ongoing, is a design review of the infrastructure design.


Closer to sea level, the design has been finalized and an architect has been secured for the refurbishment of the space for the CTAO’s lower elevation office located in Breña Baja, which is about an hour drive from the observatory. In addition to workspace for approximately 15 staff, the design includes plans for meeting space and a control room for the potential remote operation of the array.

In its first attempt to detect a gamma-ray source, the Large-Sized Telescope prototype (LST-1) successfully detected its first gamma-ray signal on 23 November 2019 when it pointed to the Crab Nebula, which is considered the standard candle in very  high-energy  astronomy. Preliminary analyses show a very clear detection of a gamma-ray signal coming from the source, reassuring the team’s expectations that the telescope is performing as designed. Read the announcement.

Paolo Calisse joined the CTAO in January 2019 as the CTA-North Site Manager. Paolo will have a key role in supervising CTAO activities at the CTA-North site at Observatorio del Roque de los Muchachos in La Palma. He will supervise the integration and commissioning of the four Large-Sized and fifteen Medium-Sized Telescopes at the site. He will also provide the link between the site and the CTAO Project Office in Bologna, as well as the interface between the local project stakeholders and the hardware and software contributors. Once the array is operational, he will be responsible for the on-site management of science and technical operations. Read the announcement.

The first phase of the CTA-North site’s infrastructure design commenced in August 2019 as CTA site hosting partner the Instituto de Astrofisica de Canarias (IAC) initiated a contract for the infrastructure design and planning of the remaining Large-Sized Telescope (LST) foundations (LST 2, LST 3 and LST 4) and one of the Medium-Sized Telescopes (MST), the MST 3, as well as the auxiliary instrumentation for the site (three weather stations and several atmospheric monitoring and calibration devices). This project also includes roads and fencing, as well as accesses, underground services and power networks, to complete the infrastructure for the central part of the array. Read the announcement.

On the night of 14-15 December 2018, the Large-Sized Telescope (LST) prototype recorded its first Cherenkov light on the northern site of the Cherenkov Telescope Array (CTA), located at the Instituto de Astrofísica de Canarias’ (IAC’s) Observatorio del Roque de los Muchachos (ORM), on the Canary island of La Palma.


Read the full story here.

On Wednesday, 10 October 2018, more than 200 guests from around the world gathered on the northern array site of the Cherenkov Telescope Array (CTA) to celebrate the inauguration of the prototype Large-Sized Telescope (LST). The telescope, named LST-1, is intended to become the first of four LSTs on the CTA-North site, which is located on the existing site of the Instituto de Astrofisica de Canarias’ (IAC’s) Observatorio del Roque de los Muchachos located in the municipality of Villa de Garafia on the island of La Palma.


Read the full story here.

Daniel López / IAC

On 25 September 2018, the team constructing the LST prototype telescope, achieved the final major milestone of the construction project when they successfully installed the camera. The camera, which covers a field of view of around 4.3 degrees, is composed of 1855 photomultiplier tubes (PMTs) – devices that transform the light into an electrical signal. After a complete performance review at the Institut de Fisica d’Altes Energies (IFAE) in Barcelona (Spain), performed with LST members from Madrid (CIEMAT, UCM) as well as France (CPPM, LAPP) and Japan (ICRR, Kyoto University), the camera was shipped to La Palma at the end of the summer, but it was not until 24 September that it was finally transported up to the ORM and then successfully installed on 25 September.


Read the full story.

During 21 and 22 June, the LST1 prototype hit another structural milestone when its camera support structure (CSS) was installed. With the addition of the CSS – the parabolic arc holding the camera on the mirror dish – the LST is taking its final, spectacular form. Read more here:

On 17 February, the LST prototype structure was completed when the dummy counterweight was put into place. The counterweight structure resembles the camera support structure but is somewhat shorter and heavier, allowing the dish to turn toward the park position. In this position, 198 segmented mirrors will be mounted in the coming months. The dummy counterweight will be removed before the installation of the proper camera support structure in June 2018. Read more:

In addition to the LST prototype milestones, there was considerable activity on CTA’s northern hemisphere site in the second half of 2017. The CTA Project Office, along with the Managing Director, made several visits to the island to meet with local authorities and to continue infrastructure surveys and planning. With the topographical survey and power concept studies complete, the positions of the telescopes, buildings and underground services on the site are now defined and detailed designs can begin for the array’s power distribution system.


Tendering will start in 2018 for the first phase of the design contract with local architects and engineers, which includes starting the environmental impact assessments for the site. The detailed design and obtaining the necessary permits for construction, will take approximately one year. If all goes as planned, the first phase of construction should start in the middle of 2019.

On 4 December 2017, The LST prototype, under construction at Roque de los Muchachos Observatory in La Palma, reached an important milestone when its 18-ton mirror dish, mostly made of reinforced carbon fiber tubes, was lifted to the lower structure successfully. After careful preparation, the dish was lifted 18 meters above the ground and secured using a 200-ton crane. The whole operation only took four hours. A big congratulations to the team for bringing the telescope one step closer to operation! Watch the time lapse on YouTube:

In July, the prototype’s center pin was installed in the middle of the foundation to support the mechanical structure of the LST. The circular 23 m diameter rail and six wheel bogies used to spin the telescope have been installed. The lower structure, which is the mount on which the mirror dish will be placed, is near completion.

The CTA northern hemisphere array site in La Palma has been full of activity recently as site infrastructure design studies commence.  Work on the site’s infrastructure, which is being coordinated by the CTA Project Office, is well underway. A Madrid-based company, Geo-Avance, has been contracted to conduct the topographical study of the site, which is estimated to begin in May. The study will report on the site’s characterization by taking detailed accounts of the contours of the rolling, rocky hills of the site and giving a bird’s-eye view with aerial photography. These details will be integral to design decisions for the placement of telescopes, roads and underground services (power and data). Preparations are underway for the geotechnical study, which is estimated to begin this summer.

The foundation for a prototype of CTA’s largest telescope, the Large-Sized Telescope, was completed on 11 January 2017. The main elements of the foundation, the telescope and the camera access tower foundations, were constructed with 620 cubic metres of concrete or about 1,500 tonnes! This massive amount of concrete will help keep the telescope and its mirror (400 square metres) stable with winds up to 200 km per hour. Additionally, a large area of the land next to the foundation has been flattened so it can be used to assemble the telescope structure.


The next step is to install the circular 23 m diameter rail used to spin the telescope, followed by the installation of six wheel bogies. The telescope structure is planned for installation between April and October. The camera access tower should be built in September and, in the final step, the camera is scheduled to be installed in November 2017.

The hosting agreement with the Instituto de Astrofisica de Canarias (IAC) was signed in September 2016 (read the press release). The agreement allows the construction of the CTA northern array to proceed at the Roque de los Muchachos site and ensures access to the infrastructure and common services needed for the operation of the Observatory.

On Friday, 9 October 2015, the first stone-laying ceremony for the Large-Sized Telescope (LST) prototype took place at the Roque de los Muchachos Observatory (ORM) on the island of La Palma (read the press release).