German astronomer Johannes Kepler, known for his laws of planetary motion and the namesake of a NASA space telescope, has discovered a new clue as to why the Sun went dark for 70 years. From 1645 until 1715, the Sun experienced a period of depressed solar activity known as the Maunder minimum, named after the English astronomer Edward Walter Maunder. This period was named after Maunder's discovery. Scientists from Nagoya University in Japan have reinterpreted Kepler's observations of sunspots made in 1607 using a camera obscura to reveal the origin of this period. The discovery could help astronomers unravel the mysteries of the solar cycle. Previously, astronomers have relied on tree-ring observations to understand solar cycles, but this study found that Kepler's observation likely occurred at the tail-end of Solar Cycle -13, rather than the beginning of -14.