The High Energy Stereoscopic System
The HESS (High Energy Stereoscopic System) telescope allows scientists to explore gamma-ray sources with intensities at a level of a few thousandths of the flux of the Crab nebula (the brightest steady source of gamma rays in the sky). H.E.S.S. is located in Namibia, near the Gamsberg mountain, an area well known for its excellent optical quality.
The first of the four telescopes of Phase I of the H.E.S.S. project went into operation in Summer 2002; all four were operational in December 2003, and were officially inaugurated on September 28, 2004. A much larger fifth telescope - H.E.S.S. II - is operational since July 2012, extending the energy coverage towards lower energies and further improving sensitivity (you get better images with two eyes).
The largest of its kind, H.E.S.S. IIstands in the foreground of this photo.
Tilted horizontally it reflects the inverted landscape of the Namibian desert in a segmented
mirror 24 meters wide and 32 meters tall, equal in area to two tennis courts.
The H.E.S.S.
H.E.S.S. is a system of Imaging Atmospheric Cherenkov Telescopes that investigates cosmic gamma rays in the energy range from 10s of GeV to 10s of TeV. The name H.E.S.S. stands for High Energy Stereoscopic System, and is also intended to pay homage to Victor Hess, who received the Nobel Prize in Physics in 1936 for his discovery of cosmic radiation.
What is Cherenkov telescope?
Most ground-based telescopes with lenses and mirrors are hindered by the Earth's nurturing, protective atmosphere that blurs images and scatters and absorbs light. But the H.E.S.S. II telescope is a cherenkov telescope, designed to detect gamma rays - photons with over 100 billion times the energy of visible light - and actually requires the atmosphere to operate. As the gamma rays impact the upper atmosphere they produce air showers of high-energy particles. A large camera at the mirror's focus records in detail the brief flashes of optical light, called cherenkov light, created by the air shower particles.
Why stereoscopy is essential to their work?
The H.E.S.S. II telescope operates in concert with the array of four other 12 meter cherenkov telescopes to provide multiple stereoscopic views of the air showers, relating them to the energies and directions of the incoming cosmic gamma rays.
One of the Best in the World
The H.E.S.S. observatory is operated by the collaboration of more than 170 scientists, from 32 scientific institutions and 12 different countries: Namibia and South Africa, Germany, France, the UK, Ireland, Austria, Poland, the Czech Republic, Sweden, Armenia, and Australia. To date, the H.E.S.S. Collaboration has published over 100 articles in high-impact scientific journals, including the top-ranked ‘Nature’ and ‘Science’ journals. H.E.S.S. was awarded in 2006 the Descartes Prize of the European Commission - the highest recognition for collaborative research - and in 2010 the prestigious Rossi Prize of the American Astronomical Society. In a survey in 2006, H.E.S.S. was ranked the 10th most influential observatory worldwide, joining the ranks with the Hubble Space Telescope or the telescopes of the European Southern Observatory ESO in Chile.
