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Description
The continuous spatio-temporal evolution (the so-called 'Maunder butterfly diagram') of sunspot activity was available since 1874 using data from the Royal Greenwich Observatory since 1875, extended by SOON network data after 1976. Here we present a new extended butterfly diagram of sunspot group occurrence continuously since 1826, using the recently digitized data from Schwabe (1826-1867) and Spoerer (1868-1874). The wings of the diagram are separated using a recently developed method based on long gaps in sunspot group occurrence in different latitude bands. Characteristic latitudes, corresponding to the start, end and the latitudinal span of the wings, F-, L- and H-latitudes, respectively, as well as times and asymmetries of the butterfly wings are analyzed. The F-latitude depict a weak tendency, especially in the S-hemisphere, to follow the wing strength (quantified in the total sum of monthly numbers of sunspot groups). The H-latitudes are highly significantly correlated with the strength of the wings during cycles 12-23. The L-latitudes show no clear relation to the wing strength. Overall, stronger cycle wings tend to start at higher latitudes and have greater wing's span. A strong (5-6)-cycle periodic oscillation was found in many latitudinal parameters, such as dates of the start and end of the wings and, most pronounced, in the difference between the wing lengths in the two hemispheres. A barely significant oscillation of about 10 cycles period is found in the asymmetry of the L-latitudes. The new long database of butterfly wings and the results based on it provide new observational constraints to the spatio-temporal distribution of sunspot occurrence and their solar cycle related time-latitude evolution.
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