Abstract
Early observations of sunspot were realised by the naked eye. Possible
utilization of these records for studying the long-term change in the Sun is
discussed here. Other historical sunspot observations with camera obscuras are
also discussed. Moreover, the best record of the behaviour of the Sun exists
for the last four centuries thanks to the observations of sunspots with
telescope. These observations should allow us to know the number, position, and
area of sunspots as well as some relevant episodes (Maunder Minimum, optical
flares, etc.). Rudolf Wolf developed the first reconstruction of solar activity
in the 19th century. The next reconstruction was made by Hoyt and Schatten in
1998 by improving the database and using a new methodological approach. Here
some mistakes, pending tasks and minor improvements are discussed.
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