Evaluation of Devasthal site for optical astronomical observations

Based on an extensive site survey conducted during 1980-1990 in the Shivali k Hills of the Central Himalayan range, a promising site Devasthal has been identified. The longitude and latitude of Devasthal Peak: are 79 degrees 4 1' E and 29 degrees 23' N. It is situated at an altitude of 2540 m and abou t 50 km by road from Nainital toward:; East. The surroundings of Devasthal are thinly populated and it is logistically well suited for establishing mo dern optical observational facilities. The prevailing wind direction at Dev asthal is NW. For a large fraction of the night, time, variation in the amb ient temperature was less than a degree and wind speed was less than 10 m/s . During; spectroscopic nights (> 200 in a year) relative humidity is less than 80% for about 70% of the time. During 1997 and 1998 seeing measurement s using differential image motion techniques have been carried out close to ground at two locations namely Site 1 and Site 2 in Devasthal. Our observa tions for Site 1 carried over 88 nights yield a median seeing value of 1'.' 4. For Devasthal Site 2 observations carried over 37 nights yield a median seeing value of 1'.'1 Devasthal Site 2 has therefore been selected for loca ting a modern 3 m optical telescope.