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Kepler's 400-year-old sunspot sketches helped solve a modern mystery
A sharp decline in sunspot activity in the 17th century has long puzzled astronomers.
A Benedictine monk in 807 thought he'd observed Mercury passing in front of the Sun when, in reality, he had witnessed a sunspot; similar mistaken interpretations were also common in the 12th century. German astronomer Gustav Spörer noted the steep decline in 1887 and 1889 papers, and his British colleagues, Edward and Annie Maunder, expanded on that work to study how the latitudes of sunspots changed over time. That's why Hisashi Hayakawa of Nagoya University in Japan and co-authors turned to Kepler's drawings of sunspots for additional insight, which predate existing telescopic observations by several years.
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