Sky transparency over Naini Tal : a retrospective study

We present an analysis of the atmospheric extinction coefficients measured during 1964 to 1999 in broad-band photometric passbands at U.P. State Observatory, Naini Tal. The extinction properties are also studied from the monochromatic extinction measurements carried out during 1970 to 1978. It is observed that except the yearly variation, no noticeable long term variation in extinction has been found over last 35 years. The extinctions in the ultraviolet region were found low at Naini Tal in comparison to other sites in the world. The extinctions due to aerosols are observed to be the minimum