Reanalysis of Horrebow notebooks yields sunspot position records for 1761 and 1764-1777 that produce a butterfly diagram matching the structure seen in 19th-20th century data.
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Annual sunspot numbers for 1-969 CE show 91 cycles averaging 10.6 years long, including a grand minimum around 650-730 CE and an extreme event in 774 CE.
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Christian Horrebow's Sunspot Observations -- II. Construction of a Record of Sunspot Positions
Reanalysis of Horrebow notebooks yields sunspot position records for 1761 and 1764-1777 that produce a butterfly diagram matching the structure seen in 19th-20th century data.