BTA Telescope (Arkhyz)

The BTA Telescope — the Large Altazimuth Telescope — is the largest optical telescope in Russia and Eurasia, with a primary mirror 6 meters in diameter. It is installed at the Special Astrophysical Observatory of the Russian Academy of Sciences at the foot of Mount Pastukhov, in the settlement of Nizhny Arkhyz in the Zelenchuksky District of Karachay-Cherkessia. From 1975 to 1993, the BTA was the largest telescope in the world.

History

The observatory was established in 1966 as a center to operate what were then the largest instruments of their kind — the BTA telescope and the RATAN-600 radio telescope. The BTA's primary mirror was installed in October 1974, and the telescope itself went into operation on December 30, 1975. It immediately took first place in the Guinness Book of Records as the largest optical telescope in the world and held that title until 1993, when it was surpassed by the telescopes of the Keck Observatory in Hawaii.

Over half a century of operation, the BTA has played an important role in space research and in the development of optical and astrophysical technology. Its dome is the largest astronomical dome in the world.

The Mirror

The primary mirror is 6 meters in diameter (more precisely, 6.05 m) and weighs 42 tons; the telescope together with its structure weighs about 850 tons. The telescope has repeatedly faced problems with mirror quality and degradation over time: the first mirror turned out to be defective and was replaced in 1979. In 2007 a decision was made to refurbish that original mirror and return it to the telescope, but this step did not bring the desired result either.

Today the BTA uses a different mirror. In 2025 its reflective coating was renewed (an aluminizing procedure was carried out), and on August 4 the mirror was returned to the telescope; observations have continued with almost no downtime since.

Getting There and What to See

The observatory is open to visitors: daytime excursions to the telescope and nighttime observation sessions are held, during which visitors can see the planets and the rings of Saturn through the telescope. The BTA building can be reached by a paved road from the entrance to the settlement of Nizhny Arkhyz.