G. Montemagno, Caltagirone 1870
Size 270×340 mm
INAF-Palermo Astronomical Observatory, Historical Archives
The three plates on show were part of a six watercolour sequence illustrating the various phases of the aurora which took place in the nights of 24 and 25 October 1870. It was not an unusual occurrence, during the maximum solar activity, to observe auroras at relatively low latitudes, given the purity of the sky at that time. The 1870 auroras were quite spectacular and they were accompanied by the usual geomagnetic perturbations which take place simultaneously. The aurora lights were spectroscopically analyzed in the 19th century, but the wavelength of the aurora spectral lines was difficult to be determine with some precision. Nowadays we know that auroras are produced by charged particle in the solar wind interacting with the ionosphere (upper part of the terrestrial atmosphere) and that they occur more frequently in the periods of maximum solar activity. [i.c., d.r.]
Bibl.: Tacchini 1870; Chinnici 2009, p. 235.