High Energy Stereoscopic System (H.E.S.S.) is an array of four imaging atmospheric Cherenkov telescopes located in the Khomas Highland region of Namibia. It is used to study very-high-energy gamma rays from astronomical objects such as active galaxies, pulsars and supernova remnants.
The system consists of a central telescope with a mirror area of 107 m2 and four smaller telescopes with mirror areas of 24 m2 each. The telescopes are positioned at the corners of a square with sides of 120 m, which gives H.E.S.S. a field of view of about 2% of the sky at any one time.
HESS was inaugurated in 2002 and has been fully operational since 2004. In 2005, it discovered the first TeV gamma-ray source outside our Galaxy: the Galactic Centre black hole Sgr A*. Since then, HESS has made many important discoveries including:
the discovery that most Galactic cosmic rays are accelerated in supernova remnants;
the detection of extremely energetic particles from distant active galaxies;
the measurement of the highest energy photons ever seen from Earth;
and the discoveryof unexpected sourcesof very high energy gamma rays such as millisecond pulsars and “dark” matter annihilation sites..