ASTRI (Astrofisica con Specchi a Tecnologia Replicante Italiana, in English: Astrophysics with Italian Replicating Technology Mirrors) is a project aimed at the technological and scientific development of the next generation of IACT (Imaging Atmospheric Cherenkov Telescope) telescopes, for ground-based gamma-ray astronomy in the energy band between 1 TeV and a few hundred of TeV.
It was initially financed as a flagship project of the MUR; it now represents one of the major ground-based astronomy projects led by INAF. The ASTRI-Horn prototype telescope, 4 m in diameter, was built on the slopes of Mount Etna (Sicily) at the Serra la Nave site, and entrusted to the management of the INAF-Astronomical Observatory of Catania (INAF-OACt).
It was named in honor of Guido Horn D’Arturo, the Italian astronomer who invented tessellated mirrors for telescopes.
ASTRI-Horn is the first telescope for Cherenkov astronomy with a wide field of view (10 degrees) to have adopted the very compact, aplanatic, two-mirror optical configuration of the Schwarzschild-Coudertype, with a camera equipped with SiPM silicon detectors.

The structure of the ASTRI telescopes. Credits: ASTRI.

Exploiting the experience thus developed, the National Institute for Astrophysics (INAF) is now engaged in the implementation of the second stage of the project, a group of nine telescopes Cherenkov - called ASTRI Mini-Array - at the Teide Observatory, on the island of Tenerife (Canary Islands, Spain). The telescopes will be built approximately 250 m apart. Telescopes and cameras are similar to the ASTRI-Horn ones, with some improvements.

The project exploits also the on-site support of the Istituto Astrofisico de Canarias (IAC), which hosts the infrastructure, and the Fundacion Galileo Galilei (FGG, governed by INAF), while other international institutions (Universidade de São Paulo, - USP, Brazil, North-West University Sud Africa, Université de Geneve, Switzerland) are contributing at various levels.
The ASTRI-Horn and ASTRI Mini-Array represent the precursor of the SST telescopes (Small Size Telescopes) at the southern site of the CTAO Observatory (Cherenkov Telescope Array Observatory), which will become operational in Chile, at Paranal, in 2027.

The ASTRI-Horn prototype telescope is located at the headquarters of the Catania Astronomical Observatory in Serra La Nave (Catania). Credits: ASTRI.

The main aim of ASTRI Mini-Array is to carry out, starting from 2025, for the first time, stereoscopic observations in Cherenkov light with wide-field telescopes and to study astronomical sources in the gamma-ray band from 1 to 200 keV.
Thanks to the optimal angular and energy resolutions of the ASTRI Mini-Array, the observations will be complementary to the direct high-altitude particle detectors already operating in the northern hemisphere such as LHAASO (Large High Altitude Air Shower Observatory) e HAWC (High-Altitude Water Cherenkov Observatory) which, in parallel, are monitoring the sky in the same band.

The ASTRI Mini-Array construction site. Credits: ASTRI.

Rendering of the ASTRI Mini-Array. Credits: ASTRI.