CTAO's site in the southern hemisphere

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CTAO’s southern hemisphere array or CTAO-South is located less than 10 km southeast of the European Southern Observatory’s (ESO’s) existing Paranal Observatory in the Atacama Desert in Chile, which is considered one of the driest and most isolated regions on Earth – a paradise for stargazers. The telescope array along with the support facilities located in Santiago, Chile, is known as the “Southern Station.”

CTAO-South site. Credit: CTAO ERIC

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Array Coordinates:

Latitude: 24º 41′ 0.34″ South
Longitude: 70º 18′ 58.84″ West

Proposed Array Layout

While the northern hemisphere array will be more limited in size and will optimize the CTAO’s low- and mid-energy ranges from 20 GeV to 5 TeV, the southern hemisphere array will be optimized for the medium and high-energy ranges of the CTAO, from 150 GeV to 300 TeV, which implies the specialization of the southern array in Galactic targets. The approved Alpha Configuration will include an array spread over three square kilometers with 14 Medium-Sized Telescopes to cover CTAO’s core energy range and 37 Small-Sized Telescopes to cover CTAO’s highest energy gamma rays.


The Alpha Configuration does not consider LSTs in the CTAO southern array, but it includes the preparation of the foundation for four of them, as well as the foundation for three more SSTs, to allow for the construction of these telescopes in a future enhancement of the array. The positions of these telescopes are also included in the layout, which defines the geographical positions of the elements in the array (telescopes, calibration systems and atmospheric characterization devices).


Layout of the CTAO southern array in the Atacama Desert (Chile), according to the Alpha Configuration.