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Improving sunspot records: Solar drawings of the late 19th century from the Royal Astronomical Observatory of Lisbon

Abstract:

The reconstruction of solar activity in the past is very important for a number of astrophysical and geophysical studies. In this work, we recovered and analysed a collection of historical solar drawings made by the Portuguese astronomer Manuel S. Melo e Simas in 1895-6 and 1898 and preserved in the archive of the Royal Astronomical Observatory of Lisbon. We have computed the sunspot number from these observations and compared it with the standard International Sunspot Number. Moreover, we have also analysed a set of detailed drawings of a large sunspot group observed in 1898 March. That group has been associated with the great geomagnetic storm of 1898 March 15.