Auroral Observations in Finland-Visual Sightings during the 18th and 19th Centuries

Abstract

Systematic naked eye sightings of northern lights started in Finland in 1748. Such observations were carried out for about 100 years at two places in Southern Finland. All observations were compiled and published by Hällström (1847). Auroral occurrence frequencies in this compilation obey well the semiannual variation and the 11-year sunspot cycle when compared with other coeval auroral and magnetic data available in Europe. In the middle of the 100-year auroral series there was an anomalous period of very low auroral occurrence, known as Dalton's solar activity minimum, lasting about three decades from 1795 to 1825. As a signature of Dalton's minimum, auroras were totally absent from the sky in Southern Finland for the 10 years 1806-1815.