From the Royal Observatory at Greenwich he observed the Sun and recorded sunspots on every possible day for forty years, assisted by his second wife, Annie Scott Dill Maunder, née Russell (1858–1947). He established the Sun’s differential rotation from the motions of sunspots at different latitudes, and identified the relationship between solar activity and disturbances in the Earth’s magnetic field. The Maunders also studied the history of astronomy; his research, published in 1894 and 1922, revealed what is now called the Maunder minimum.