  We revise the sunspot observations made by Galileo Galilei and Christoph
Scheiner in the context of their controversy on the nature of sunspots. Their
sunspot records not included in the current sunspot group database, used as a
basis to calculate the sunspot group number, are analyzed. Within the
documentary sources consulted in this work, we can highlight the sunspot
observations by Scheiner included in the letters sent under the pseudonym
Apelles to Marcus Welser and the first sunspot observations made by Galileo,
which can be consulted in Le opere di Galileo Galilei. These sunspot
observations would extend the temporal coverage for these two observers and
filling some gaps in the current group database in the earliest period where
the data available is sparse. Moreover, we have detected changes in the quality
of the sunspot drawings made by Galileo and Scheiner in their observation
series affecting to the number of groups recorded by the two observers. We also
compare these records with sunspot observations made by other astronomers of
that time. According to this comparison and regarding the same observation
days, Scheiner was generally the astronomer who reported more sunspot groups
while Harriot, Cigoli, and Galileo recorded a similar number of groups. We
conclude these differences are mainly because of the observational method used
by the observers.

Solar and Stellar Astrophysics