CTAO's site in the northern hemisphere

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The CTAO’s northern hemisphere array or CTAO-North is located on the island of La Palma in the Canary Islands (Spain) at the Instituto de Astrofísica de Canarias’ (IAC’s) Observatorio del Roque de los Muchachos in Villa de Garafía . At 2,200 metres in altitude and nestled on the slope below the rim of an extinct volcanic crater, the site currently hosts a prototype of one of the CTAO’s Large-Sized Telescopes, the LST-1. In addition to the telescope array, the CTAO will have an operations building and calibration devices on site, as well as an office at sea level. The sum of these facilities is known as the “Northern Station.”

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Array Coordinates:

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

Proposed Array Layout

While the southern hemisphere array will span from the medium to the high end of 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. The approved Alpha Configuration hosts four Large-Sized Telescopes to capture the low-energy gamma rays and nine Medium-Sized Telescopes to cover CTAO’s core energy range. A prototype of an LST, the LST-1, was completed on site in October 2018 and is foreseen to become the CTAO’s first telescope once it has completed its commissioning and is accepted by the CTAO.


The proposed layout of CTAO-North, which defines the geographical positions of the elements (operations building, 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.


Layout of the CTAO northern array on La Palma (Spain), according to the Alpha Configuration.

Operations Building

CTAO-North Operations Building Rendering

Rendering of the CTAO Operations Building (credit: Arch. Gabriel Henríquez Pérez S. L. P.)

Planning and preparations for the operations building, which will be built in a prominent position near the entrance of the Roque de los Muchachos Observatory, is underway. Staff in this building will operate and maintain the CTAO-North telescopes and infrastructure with support from a smaller office located closer to sea level. The building design has been finalised and work has begun to prepare the site for construction, including a geotechnical site investigation commissioned by the IAC.