the totality of climatic factors that determine a given locality’s suitability for conducting astronomical observations. These factors include the number of clear days and nights, the transparency of the atmosphere, the number of days and nights with maximum transparency, the stability of optical characteristics of the atmosphere, the degree of dust in the air, the brightness of the night sky’s background, the frequency of occurrence of dew and fog, and the intensity of atmospheric turbulence, which determines the degree of flicker and twinkling of stellar images. The astronomical climate determines the quality of the images of celestial objects during astronomical observations and the average annual number of days and nights which are suitable for observations. It also plays an important role in selecting the construction sites for astronomical observatories with large telescopes. In the USSR favorable astronomical climatic conditions exist in regions of Eastern Siberia, Middle Asia, the Crimea, the Caucasus, and the southern European part of the country. Special astronomical expeditions conduct studies of astronomical climates.
N. B. DIVARI