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Cometary tails visually manifest the solar wind and became an initial hint for its discovery. While the solar wind is being directly monitored with satellites, its time series before the space age has been controversially reconstructed with multiple proxies. Recently, archival reports of cometary plasma tails have been subjected to consideration to indirectly measure the solar wind but brought conclusion that no plasma tails had been reported prior to 1769 probably due to their brightness. However, historical records have occasionally reported comets with two tails even before 1769. These cases have been tentatively associated with visual reports of cometary plasma and dust tails. Therefore, we examined three such cases (C/1577 V1, 1P/837, and 1P/760), and compared the descriptions in historical records with calculated direction of their plasma tails. Our comparisons show that the records and calculations agree in these cases and plasma tails were visually recorded corresponding to these three great comets. These cases certify the capability of plasma tail observations with the unaided eye even before 1769, qualitatively imply their extreme brightness, proximities with the Sun and the Earth, relative enhancements of UV radiations, and interaction of cometary neutral atmosphere with solar wind plasma and magnetic field, while the lack of their detailed length or kink hinders us from their quantitative measuring. Further investigations will likely lead to the re-discovery of even more visual evidence of cometary plasma tails and, hence, improve our understanding on past space climate.

Three case reports on the cometary plasma tail in the historical documents