Iwahashi Zenbei's Sunspot Drawings in 1793 in Japan

TL;DR

This paper analyzes 18th-century Japanese sunspot drawings by Iwahashi Zenbei, revealing observational details, comparing them with global data, and highlighting their significance for understanding historical solar activity and Japanese astronomical knowledge.

Contribution

It identifies and dates Zenbei's sunspot drawings, locates the observation site, and contextualizes these observations within global solar data, filling gaps in historical sunspot records.

Findings

The drawing dated 26 August 1793 was confirmed.

Observations lasted over a year, providing extended data.

The drawings offer valuable non-European solar observations.

Abstract

Three Japanese sunspot drawings associated with Iwahashi Zenbei (1756-1811) are shown here from contemporary manuscripts and woodprint documents with the relevant texts. We revealed the observational date of one of the drawings to be 26 August 1793, and the overall observations lasted for over a year. Moreover, we identified the observational site for the dated drawing at Fushimi in Japan. We then compared his observations with group sunspot number and raw group count from Sunspot Index and Long-term Solar Observations (SILSO) to reveal its data context, and concluded that these drawings filled the gaps in understanding due to the fragmental sunspots observations around 1793. These drawings are important as a clue to evaluate astronomical knowledge of contemporary Japan in the late 19 th century and are valuable as a non-European observation, considering that most sunspot observations up to mid-19 th century are from Europe.