6m telescope

The 6-m alt/az mounted telescope (BTA - Big Telescope Alt-azimuth) is the largest optical telescope in Eurasia. Special Astrophysical Observatory RAS provides continual operation of the telescope on requests of both Russian and foreign scientists. Scientific equipment necessary for astrophysical observations is made and designed by the staff of the observatory. The telescope is located near Mt.Pastukhova at the altitude of 2070 m above sea-level. The co-ordinates of the site are longitude 41^o26'30", latitude +43^o 39'12".

BTA

Main mirror diameter 6.05 m

Focal length 24 m

Light collecting area 25.1 sq.m

Wavelength range 0.3 - 10 mkm

Angular resolution 0.6 arcsec

Angular resolution with the application
of speckle interferometry techniques 0.02 arcsec

Mass of the main mirror 42 tons

Total telescope mass 850 tons

Telescope height 42 m

Dome height 53 m

Optical scheme of the telescope

The main mirror (MM) is parabolic in shape and has a focal length of 24 meters. Its diameter is 605 cm. The diameter of the cylindrical prime focus cage is 2 meters. Some removable optical devices together with the drive mechanisms for the movements of the lens corrector and the hyperbolic secondary mirror are located here. Laboratory tests have shown that 90% of the energy is concentrated within a circle of 0.8" in diameter. The image diameter is determined by the micro-climate in the dome, as well as the thermal state of the mirror. Under favorable conditions (small temperature difference between the MM, and the air inside the dome and outside it), the size of stellar images is limited by atmospheric turbulence.

The optical scheme of the telescope guarantees working at the prime focus (f/4) and also at two Nasmyth foci (f/30). The time required to switch the beam from one focus to another is 3-4 minutes, which makes it possible to carry out observations on various focal distances within a single night.