He was a sunspotter
(1822 – 1895) A German astronomer noted for his studies of sunspots and sunspot cycles. He was the first to note the prolonged period of low sunspot activity from 1645 to 1715 that is now called the Maunder Minimum.
1. The Sporer Minimum is a period of low sunspot activity that occurred from roughly 1420 to 1570.