Historical sunspot observations: A review

Early observations of sunspots were made by the naked eye. We discuss here the possibilities to use these records to study the long-term change in the Sun. Other historical sunspot observations with camera obscura are also discussed. The best record of the behaviour of the Sun is available for the last four centuries thanks to the observations of sunspots with telescope. These observations allow us to know the number, position, and area of sunspots as well as some specific episodes like the Maunder Minimum, optical flares, etc. Rudolf Wolf developed the first reconstruction of solar activity in the 19th century. Another reconstruction was made by Hoyt and Schatten in 1998 which improves the database and uses a new methodological approach. Here we also discuss some mistakes, pending tasks and minor improvements related to sunspot observations. (C) 2007 COSPAR. Published by Elsevier Ltd. All rights reserved.