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Between 1761 and 1776, Christian Horrebow made regular observations ofsunspots from Rundetaarn in Copenhagen. Based on these observations he writesin 1775 that "it appears that after the course of a certain number of years,the appearance of the Sun repeats itself with respect to the number and size ofthe spots". Thus, Horrebow hypothesized the idea of a cyclic Sun severaldecades before Heinrich Schwabe discovered the solar cycle and estimated itsperiod. This proves the ability of Horrebow as a sunspot observer. In thisarticle, we present a general overview of the work of Christian Horrebow,including a brief biography and a complete bibliography. We also present atranslation from Danish to English of his writings on sunspots in the DanskHistorisk Almanak. These writings include tables of daily sunspot measurementsof which we discuss the completeness.

Christian Horrebow's Sunspot Observations -- I. Life and Published Writings