The 3.6m Devasthal (Hindi: देवस्थल) Optical Telescope is a clear-aperture Ritchey–Chrétien telescope built by Aryabhatta Research Institute of Observational Sciences (ARIES) and is located at the Devasthal Observatory site near Nainital, Kumaon, India. ARIES operates another 1.3m telescope at the same location. The telescope was activated remotely on 31 March 2016 by Indian Prime Minister Narendra Modi and Belgian Prime Minister Charles Michel from Brussels. The telescope optics were built in collaboration with the Belgian firm Advanced Mechanical and Optical System (AMOS).

3.6m Devasthal Optical Telescope

ARIES 3.6m Telescope at Devasthal, India
Part of	Devasthal Observatory
Location(s)	Nainital district, Kumaon division, Uttarakhand, India
Coordinates	29°21′39″N 79°41′04″E / 29.36088°N 79.68433°E / 29.36088; 79.68433
Organization	Aryabhatta Research Institute of Observational Sciences
Altitude	2,540 m (8,330 ft)
Wavelength	350 nm (860 THz)–5,000 nm (60 THz)
Telescope style	optical telescope Ritchey–Chrétien telescope
Diameter	3.6 m (11 ft 10 in)
Focal length	32.4 m (106 ft 4 in)
Website	www.aries.res.in/facilities/astronomical-telescopes/360cm-telescope
Location of 3.6m Devasthal Optical Telescope
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The 3.6m DOT is currently the largest reflecting telescope in Asia.^[1] The telescope intends to fill a large longitudinal gap in the 4m class of telescopes in the Asia region. The telescope features an optical spectrograph, a CCD imager and a near-infrared spectrograph. The telescope is also the first of its kind in India that features an active optics^[2] system, featuring a wavefront sensor and pneumatic actuators which compensates for small distortions in the shape of the 4.3 tonne mirror due to gravity or atmospheric aberrations.