Sunspot Drawings by Japanese Official Astronomers in 1749-1750

TL;DR

This paper analyzes 18th-century Japanese sunspot drawings from 1749-1750, revealing their placement around the solar maximum and contributing to historical solar activity records.

Contribution

It provides the first detailed analysis of Japanese sunspot observations from 1749-1750, enhancing historical solar activity data and cross-cultural sunspot records.

Findings

Sunspot observations were made during the solar maximum in 1749-1750.

Japanese observations align with European records, aiding crosscheck of sunspot indices.

Locations and areas of sunspots were computed from historical manuscripts.

Abstract

Sunspot observations with telescopes in 18th century were carried out in Japan as well. One of these sunspot observations is recorded in an account called Sansaizusetsu narabini Kansei irai Jissoku Zusetsu (Charts of Three Worlds and Diagrams of Actual Observations since Kansei Era). We analyze manuscripts of this account to show in total 15 sunspot drawings in 1749-1750. These observations were carried out by contemporary official astronomers in Japan, with telescopes covered by zongurasus (< zonglas in Dutch, corresponding to "sunglass" in English). We count their group number of sunspots to locate them in long-term solar activity and show that their observations were situated around the solar maximum in 1749 or 1750. We also computed their locations and areas, while we have to admit the difference of variant manuscripts with one another. These observational records show the spread of sunspot observations not only in Europe but also in Japan and hence may contribute to crosscheck or possibly improve the known sunspot indices.