Between 27 and 29 May, the CTAO ERIC Council held its first in-person meeting of the year on the island of La Palma (Canary Islands, Spain), home to the CTAO northern hemisphere array, or CTAO-North. The Council is the governing body of the CTAO ERIC and includes delegates from Austria, Croatia, the Czech Republic, the European Southern Observatory (ESO), France, Germany, Italy, Poland, Slovenia, Spain, and Switzerland. Further countries—Australia, Brazil, Japan, South Africa, and the United States—are currently engaged in the process of joining as Strategic Partners or Third Parties.
Delegates representing these nations, alongside members of the CTAO Central Organisation (legally, CTAO ERIC), travelled to the island or connected remotely to discuss the Observatory’s progress and strategic direction. Prior to the formal meeting sessions, the Council undertook its first official tour of the CTAO-North site, which currently hosts four Large-Sized Telescopes (LSTs) at various stages of development by the CTAO LST Collaboration.
Arrival and Institutional Welcome
Ascending to 2,200 metres above sea level to the Roque de los Muchachos Observatory (ORM), home of CTAO-North, visitors are greeted by the impressive LSTs standing tall against the landscape.
The delegates were officially welcomed to the ORM by Valentín Martínez, Director of the Instituto de Astrofísica de Canarias (IAC), CTAO hosting partner. He provided an overview of the ORM’s evolution and the CTAO’s neighbouring instruments, including the Gran Telescopio Canarias (GTC), which some delegates also had the opportunity to tour.
Standing before the towering telescopes, the group was greeted by Patricia Márquez, CTAO-North Station Manager. She detailed the project’s progress on the island, highlighting the expansion of the sea-level office, staff growth, and the future on-site operations building. Further enriching the welcome, Ramón García, Principal Investigator of the IAC’s gamma-ray group, shared insights into the groundbreaking science the Cherenkov telescopes can deliver.
Up Close with the Telescopes
While observing the telescopes from a distance offers a magnificent overview of the array, the delegates were invited to step inside and explore two of them up close. Divided into groups, they visited LST-1, the prototype undergoing commissioning since 2018, and LST-4, which recently completed its construction phase with the installation of its camera.
At LST-1, delegates climbed the tower that supports the camera whilst in its resting position. From this vantage point, the true scale of the camera became apparent; together with its exterior framework, it measures a massive 3×3 metres.
Guided by Oscar Blanch, Technical Coordinator of the LST Collaboration, the group opened the rear of the camera to reveal the back-end systems responsible for the evaluation and recording of gamma-ray events. From this elevated platform, they also had a direct view of the mirrors and the central calibration system located in the heart of the reflector.
Additionally, Alice Donini, Technical On-Site Coordinator of the LST Collaboration, showcased the control monitors currently used for the telescope’s commissioning. By keeping a close eye on individual subsystems and meteorological conditions, operators manage the observations that test the telescopes. Ultimately, all Observatory operations will be managed from the future on-site operations building.
The visit to LST-4 provided a deeper dive into the telescopes’ structural engineering. Walking through the framework, guided by Daniel Mazin, LST Project Manager, delegates closely examined the tubular carbon fibre structure. This design not only supports the 100-tonne telescope but also keeps it remarkably lightweight, enabling it to reposition to any point in the sky in under 20 seconds. This structure represents a true engineering milestone: the segments are joined by over 600 unique nodes, perfectly shaping the reflector.
Back on the ground, Juan Cortina, Chair of the LST Collaboration Steering Committee, showed the delegates spare mirrors stored in the LST-4 work area, allowing them to appreciate their impressive size of around two square metres. During the day, the mirrors installed on the telescopes are intentionally misaligned for safety reasons. However, before observations begin, the telescope is calibrated, and the mirrors are adjusted with micron-level precision to ensure the reflector perfectly focuses Cherenkov light into the camera, which is suspended 28 metres away by an arch and carbon-fibre tension rods.
The continuous progress of these four telescopes is a testament to the hard work of the LST Collaboration. Capitalising on this momentum, a press conference held prior to the visit—featuring the LST Collaboration alongside the CTAO Central Organisation, the Cabildo de La Palma, and the IAC—announced that the official inauguration of the LST sub-array will take place on 15 October, with special guests like Prof. Takaaki Kajita, Nobel Laureate in Physics.
Looking Ahead
This visit marked not only the CTAO ERIC Council’s first official tour of the CTAO-North site but also an invaluable opportunity to witness firsthand the development of what will become the world’s most powerful gamma-ray observatory—a growing international effort made possible by the unwavering support of the CTAO ERIC Council member countries and organisations.
An exciting path lies ahead. Following the inauguration, the LST Collaboration will continue the commissioning required before the telescopes can be officially accepted and operated by the CTAO Central Organisation, and the site will soon welcome the first Medium-Sized Telescope (MST).
As the Central Organisation’s dedicated team and daily operations continue to expand on La Palma, we are getting ready for the initial operations, thus beginning to unlock the high-energy Universe.