Historical solar observations archive at the Ulugh Beg Astronomical Institute (Tashkent): catalogue of monthly averaged sunspot activity indices (1932–2000)

ABSTRACT Solar observations at the Ulugh Beg Astronomical Institute (UBAI) of the Uzbekistan Academy of Sciences (formerly the Tashkent Astronomical Observatory) have been conducted since its foundation in the late 19th century, spanning the period from 1884 to 2010. However, systematic solar observation programmes began in 1932 as part of the USSR Sun Service initiative. This paper presents an overview of the solar observations archive maintained by UBAI, focusing on systematic data collected from 1932 to 2000. As an initial step in the digitization of this archive, we converted time series of key solar activity indices into machine-readable formats. These indices include the monthly averaged relative sunspot number (Wolf number), sunspot group number, and sunspot area expressed in millionths of a solar hemisphere. The digitized catalogue has been compared with other existing sunspot data sets to assess its reliability. Our analysis shows that the historical sunspot data compiled by UBAI are consistent and reliable, representing a valuable contribution to global records of solar activity.