The Bohinj native, astronomer Marian Koller (1792- 1866), was a star of the 19th century. Today, his work is gaining in importance again, focusing on the Dalton Minimum of sunspots as a counterbalance to other explanations for global warming. Apart from Hallerstein, Koller was unparalleled among Slovenian astronomers. Above all, he enabled the success of Jožef Stefan.