The English astronomer Edward Maunder worked as a spectroscopic assistant at the Royal Observatory in London, a job that included examining sunspot activity. He traced a change in the location of these sunspots over an eleven-year cycle, beginning near the poles, and then, as activity reached its peak, moving nearer to the sun's equator. When plotted on a graph of time against latitude, this displayed a characteristic 'butterfly' pattern, giving the impression of a line of butterflies in flight towards the left of the graph. This work gave important impetus to revising contemporary theories about the sun, although the precise reason for this pattern is still not known.
Editors. "Edward Maunder plots the first sunspot ’butterfly diagram’". The Literary Encyclopedia. First published 30 August 2013
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6397, accessed 30 April 2017.]