The Baksan Neutrino Observatory is a scientific laboratory of INR RAS located in the Baksan Rivergorge in the Caucasus mountains in Russia. Cleared for building in 1967, it started operations in 1977, becoming the first such neutrino observatory in the USSR. It consists of the Baksan Underground Scintillation Telescope, located below the surface, the gallium–germanium neutrino telescope located 4,700 m.w.e. deep as well as a number of ground facilities. The Baksan Experiment on Sterile Transitions is currently being conducted at Baksan with aims of understanding sterile neutrinos. The laboratory itself is located in a 4000 meter long horizontal tunnel mined specifically for this purpose; this is in contrast to most underground physics laboratories which are placed in abandoned or still in-use mines. The entrance of the tunnel is at a valley at 1700 meters high from sea level and the tunnel itself is located under the 4000 meters tall mountain Mount Andyrchi. A small town of Neutrino was constructed in the valley in conjunction with the construction of the laboratory to house the scientists and their families. The first experiment undertaken at BNO was not underground; it was the Carpet air-shower cosmic ray experiment in 1973. Carpet relied on liquid scintillator detectors to study cosmic ray air-showers. Carpet also made discoveries of astrophysical importance, such as detecting a giant flare in the Crab Nebula in 1989. The Carpet cosmic ray experiment continues as of 2017, and it is being upgraded in to gamma ray telescope. Further upgrades are also planned. The first underground experiment, the BUST started operations in 1977. It is located 550 meters from the tunnel entrance. It detected neutrinos from the SN1987A supernova. It continues to operate. The next experiment at BNO was the Gallium-Germanium Neutrino Telescope as part of the SAGE experiment. It started operation 1986. It is located 3500 meters from the tunnel entrance. It continues to operate. In addition to the big experiments BUST and SAGE, a number of smaller experiments that benefit from the low-background location have taken place at BNO; for example, the isotopic composition of the lunar samples brought by Luna-16, Luna-20 and Luna-24 spacecraft was measured in BNO. BNO is also home to the Andyrchi air-shower array, located on the surface above BUST in the mountain slope. The array and BUST work in coincidence. BNO hosts also a small gravitational-wave detector, OGRAN. OGRAN would be capable of registering a galactic supernova, should one occur in the Milky Way. The BNO-observatory is planning a new major detector, the Baksan Large Underground Neutrino Telescope. This detector would consist of huge amounts of liquid scintillator. It would be located at the end of the laboratory tunnel. It would mainly detect neutrinos. As of 2017, the director of the observatory is Valery Kuzminov.
