This time, the research group found a 1770 aurora record in the diary of the Higashi Hakura family in Kyoto.It was written in the diary that the aurora covered half of the sky and that the aurora streaks pierced the Milky Way.As a result of calculating how the aurora looks from Kyoto based on that description, the same shape as the one drawn in the aurora picture drawn in the classic book "Seikai" of the Edo period was reproduced. ..Considering the strength of the geomagnetism, it is estimated that the 1770 geomagnetic storm was as large as or larger than the largest geomagnetic storm in the history of observation.

　The largest ever magnetic storm on record occurred in September 1859.It is called the "Carrington Event" after an English observer.Even in Japan, there is a description in Fujiwara no Teika's diary "Meigetsuki" that the aurora was seen many nights in a week in Kyoto in 9.The record of "Hoshikai" examined this time is from September 1204, 1 (July 1770th year of Meiwa), and the picture of the aurora that radiates from the mountain is famous.The aurora at this time has been witnessed in the largest number of areas in the country.

　Auroras occur in association with the occurrence of magnetic storms.Due to the explosion in the sun, a large amount of plasma is emitted together with the solar magnetic field and reaches the earth, causing a magnetic storm that temporarily weakens the earth's magnetic field.When the magnetic storm is large, the aurora becomes active in the polar regions, and it can be seen even in low latitude areas such as Japan.

　During the Edo period, there was a great deal of interest in astronomical science, and detailed records and management can be called "citizen science."The results are said to have been brought about by combining the research results of 250 years ago with the latest scientific research today.

Paper information:[Space Weather] Inclined zenith aurora over Kyoto on 17 September 1770: Graphical evidence of extreme magnetic storm