On the quality of sunspot images from observations at the STT-2 of CrAO

Abstract

We perform a statistical analysis of the quality of sunspot images on a five-point scale obtained during the maxima of cycles 20–25 from April to September 1969–2023. In total, 747 observation days were analyzed taking into account scheduled maintenance works associated with aluminizing the telescope mirrors. The image quality assessments by different observers are shown to be in good agreement. For images assessed by more than three points (275 observation days), it was obtained evidence in favor of a deterioration in the quality of images since 1979. We give reasons for the necessity of conducting timely repair and maintenance works at the solar tower telescope STT-2 of CrAO.