The Kuffner observatory is one of two telescope-equipped public astronomical observatories situated in Austria's capital, Vienna. It is situated in the West of the city's Ottakring district, on the slope of the Gallitzinberg at 302 m altitude. Originally a private research institution, it was converted into an educational astronomy facility after World War II as buildings and city lights had encroached to a degree that severely hampered scientific nightsky observations. Today the main tasks of the observatory consist in public education on astronomy, operating and preserving the historical equipment, and minor projects in scientific astronomy. The observatory was noted for its work on photometry, conducted by astronomer Karl Schwarzschild, star catalogs, and the determining of distances to other stars. The observatory has several astronomical instruments of historical interest, including a noted heliometer and large meridian circle, and also a vertical circle. The observatory's first observations were made in 1886. Scientific achievements The Kuffner observatory was constructed from 1884-1886 according to plans of Franz Ritter von Neumann. Originally it was a private research institution for which the philanthropic head of the Kuffner brewery dynasty from Lundenburg, Moriz von Kuffner financed the construction (including extensions built in 1889-1890), the equipment, and also the operation. During the years leading up to World War I the observatory became one of the most important astronomy sites in the Austro-Hungarian monarchy, and established a considerable international reputation. Carl Wilhelm Wirtz, Leo Anton Karl de Ball, Samuel Oppenheim, and most notably Karl Schwarzschild spent parts of their careers here. During his assistantship at the Kuffner observatory, Schwarzschild – who would later become the “grandfather of black hole theory”—developed a formula that allowed to calculate the relation between the intensity of faint astronomical light sources, the exposure time, and the degree of opacity created in photographic emulsions. Schwarzschild is noted for his work on advancing photographic photometry. Demise and reactivation The financial situation of the Kuffner dynasty deteriorated with the onset of World War I. The observatory was closed in 1915 and, after several failed attempts, was reopened only in 1947. The Vienna city council acquired the facility in 1987, and initiated a total refurbishment that lasted from 1989 to 1995 when it was reopened to the public under the direction of the Folk high school Ottakring as an institution for public education, a Volkssternwarte. Historical equipment The Kuffner observatory maintains four major pieces of observation equipment from