  Between 1761 and 1776, Christian Horrebow made regular observations of
sunspots from Rundetaarn in Copenhagen. Based on these observations he writes
in 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 of
the spots". Thus, Horrebow hypothesized the idea of a cyclic Sun several
decades before Heinrich Schwabe discovered the solar cycle and estimated its
period. This proves the ability of Horrebow as a sunspot observer. In this
article, we present a general overview of the work of Christian Horrebow,
including a brief biography and a complete bibliography. We also present a
translation from Danish to English of his writings on sunspots in the Dansk
Historisk Almanak. These writings include tables of daily sunspot measurements
of which we discuss the completeness.
