SPECIAL ASTROPHYSICAL OBSERVATORY - OBSERVATOIRE SPÉCIAL D'ASTROPHYSIQUE

Under the barbaric name "Special Astrophysical Observatory" coupled with the sober reference "BTA-6" is in fact one of the most mythical astronomical observatories in the world, much better known to enthusiasts as the Zelentchukkaya Observatory ! Located in the Caucasus, in the Republic of Karachayevo-Cherkessia, at an altitude of 2,070 m, it was the world's largest telescope from 1975 to 1993, with its 6 m diameter mirror, supplanting its American competitor, and no less famous, the 5 m telescope on Mount Palomar in California. At that time, humanity was just emerging from the rivalry between the two great powers for the conquest of the Moon! The Zelentchouk has an incredible history, a mixture of cutting-edge technology for its design but also errors in the manufacture of its optics, in the architecture of its dome and even in the choice of the site for its installation!

It all began on 25 March 1960 when the USSR Council of Ministers adopted a resolution to build a giant telescope with a diameter of 6 m. We do not dare to say it, but in the middle of the Cold War this decision seems to be a logical step towards the conquest of space, in which the two great powers, the United States and the USSR, have embarked on a journey to establish their technological and political supremacy. Sending satellites and then men into space, arriving first on the Moon... and outperforming the world's largest telescope, and the American one at that, are all ultimate quests the Soviets are hoping for. Once the decision to build this telescope has been taken, the country's brightest institutions are called upon to design the 6 m diameter mirror (weighing some 70 tonnes), polish it, design the plans for the dome and related technical buildings, find the right site so that it can give the full measure of its performance, etc. From Moscow to Leningrad, Lytkarino, Gorky or Kirov, many cities and economic sectors are working together to complete the project. The USSR Academy of Sciences is responsible for finding the best location, with the imperative criteria of a geographical location that makes it easy to transport the large parts of this "giant mechanic", including the main mirror of the telescope. Finally, it is the Pastukhov mountain sector, not far from the municipality of Zelentchukkaya, that is chosen, with its altitude of 2,100 m and its surface area of 50 hectares, necessary to build the main building (a 53 m high tower, topped by a 45.2 m diameter dome!), the astronomers' hotel, accommodation for maintenance staff, technical outbuildings, etc. The first parts of the 650-ton telescope were brought in in 1968, before being patiently assembled in the following years. At the same time, buildings and domes are built to the highest standards. In June 1974 one of the most difficult phases began, the transport of the mirror to the observatory... and on August 21 it arrived at its destination. During the winter of 1974-1975, the telescope went into service and seemed destined to become a new national pride. This was without an optic that is of poor quality, probably made from glass that is poorly adapted to the climatic conditions on site (temperature differences expand and contract the material, changing its shape and consequently its performance). It was therefore decided to replace it, which was done in 1978 with a new mirror that is still in operation today. But the problems do not stop there.... The dome is poorly designed, not facilitating the telescope's temperature rise, while the site is very turbulent in atmospheric terms (the images are blurred and their accuracy is affected!). What was supposed to be the telescope of all superlatives turns out to be the telescope of all difficulties! Fortunately, over time, and with the constant improvement of digital equipment, the Zelentchouk offers very suitable performances, particularly thanks to its very large diameter allowing it to track objects of very low luminosity.

The guided tour of this impressive telescope takes place twice a week in low season, on Saturdays and Sundays, and in high season on Fridays, Saturdays and Sundays, from 9am to 3pm. The duration of the visit is approximately 35 minutes. A minimum of 10 people is required to register. It is also possible to observe from the site using a 280 mm diameter telescope installed for the occasion. These evenings take place every evening, but obviously depend on the weather (the confirmation or not of the evening is usually taken one hour before the departure). In summer, appointment is given at 9:30 pm, in the village of Nizhny Arkhyz (in winter around 7:30 pm). These evenings last on average 1 hour and 45 minutes. In low and high season, and due to the altitude and climatic conditions, it is imperative to come to the site dressed warmly.

Finally, it should be noted that another astronomical observatory can be visited in the region, this time of the radio-astronomical type (an array of antennas pointing towards the sky study the radio waves emitted by the stars). It is the RATAN 600 (another poetic name) whose diameter impresses the visitor (576 m) and which is one of the largest radio telescopes in the world! It is located near Zelentchoukskaya, about 21 km from the village of Nizhny Arkhyz, at an altitude of 970 m. It is an integral part of the Special Observatory of Astrophysics of the Russian Academy of Sciences, and studies galaxies, especially those far away, as a priority. Guided tours of the site take place every day from 9:30 am to 3 pm (except on January ^1st) by reservation at 8 928 3949139. Their duration varies around 40 minutes. Less interesting and above all infinitely less spectacular than those of the 6 m telescope, they have the merit of being very inexpensive (at the latest news 120 rubles, or less than 2 €, including for non-Russian nationals).