Records of auroral candidates and sunspots in Rikkokushi, chronicles of ancient Japan from early 7th century to 887

Abstract

In this article, we present the results of the surveys on sunspots and auroral candidates in Rikkokushi, Japanese Official Histories from the early 7 th century to 887 to review the solar and auroral activities. In total, we found one sunspot record and 13 auroral candidates in Rikkokushi. We then examine the records of the sunspots and auroral candidates, compare the auroral candidates with the lunar phase to estimate the reliability of the auroral candidates, and compare the records of the sunspots and auroral candidates with the contemporary total solar irradiance reconstructed from radioisotope data. We also identify the locations of the observational sites to review possible equatorward expansion of auroral oval. These discussions suggest a major gap of auroral candidates from the late 7 th to early 9 th century, which includes the minimum number of candidates reconstructed from the radioisotope data, a similar tendency as the distributions of sunspot records in contemporary China, and a relatively high magnetic latitude with a higher potential for observing aurorae more frequently than at present. IntroductionInformation of long-term solar activity is important in the viewpoint of not only solar physics but also the relationship between solar activity and the terrestrial climate. Modern scientific data of solar activity are based on sunspot observations since the early 17 th century (Hoyt & Schatten 1998;Owens 2013; Clette et al. 2014;Savalgaard & Schatten 2016). On the contrary, in order to study the solar activity during the pre-telescopic age, there are two types of proxies: the ratio of radioactive isotopes and the records of sunspots and aurorae in historical documents (Eddy 1980;Vaquero & Vázquez 2009). Radioactive isotopes such as Carbon-14 and Beryllium-10 are used to reconstruct the group sunspot number or total solar irradiance (TSI) during the pre-telescopic age (e.g., Solanki et al. 2004;Steinhilber et al. 2009). Conversely, historical records of sunspots and aurorae can be used as another proxy for solar activity during the pre-telescopic era (e.g., Vaquero & Vázquez 2009;Riley et al. 2015).The largest solar event in the history of ground-based telescopic observations is thought to be the so-called Carrington event in 1859 (Carrington 1859). An unusually large magnetic change was recorded at low latitudes, which reached about −1600 nT. The disturbance storm index (Dst) was estimated to be −1760 nT (Tsurutani et al. 2003) and −625 nT (Siscoe et al 2006). Carrington (1859; 1863) reported a large sunspot coupled with a white flare in his study on 01 September 1859. This flare caused worldwide auroral observations even in low-latitude areas such as Hawaii, the 2 Caribbean coasts, and Japan on the following day,

Iwahashi Zenbei’s Sunspot Drawings in 1793 in Japan

“…They are of great importance to recover solar observations before the mid-19 th century (Domínguez-Castro et al, 2017;Denig and McVaugh, 2017). In this context, it must be noted that considerably longer traditions of sunspot observations are present not only in Europe (e.g., Stephenson and Willis, 1999;Willis and Stephenson, 2001) but also in East Asia or West Asia, even in pre-telescopic ages (Keimatsu, 1970;Clark and Stephenson, 1978;Willis et al, 1980Willis et al, , 1996Yau and Stephenson, 1988;Xu et al, 2000;Willis and Stephenson, 2002;Lee et al, 2004;Hayakawa et al, 2015Hayakawa et al, , 2017aHayakawa et al, , 2017bHayakawa et al, , 2017cTamazawa et al, 2017a;Goldstein, 1969;Vaquero and Gallego, 2002). After the 17 th century, these non-European astronomers began to make contact with European astronomy and some started to adopt European technology.…”

Revisiting Kunitomo’s Sunspot Drawings During 1835 – 1836 in Japan

“…Pankenier, 2013;Morgan, 2017), astronomers in East Asia also pursued solar observations including sunspots (e.g. Willis et al, 1980Willis et al, , 1996Yau and Stephenson, 1988;Willis et al, 2001Willis et al, , 2005Hayakawa et al, 2015Hayakawa et al, , 2017aHayakawa et al, , 2017bHayakawa et al, , 2017cHayakawa et al, , 2018cHayakawa et al, , 2018dTamazawa et al, 2017a). After a cultural contact with European astronomers, East Asian astronomers also began to undertake telescopic observations of sunspots activity (e.g.…”

A Transit of Venus Possibly Misinterpreted as an Unaided-Eye Sunspot Observation in China on 9 December 1874

“…The wrong usage of the terminology for sunspots to describe the transit of Venus suggests that this record was probably not made by contemporary professional astronomers in the court but by local observers. As pointed out by Willis et al (2005) and Hayakawa et al (2017b), the observers of the Chinese historical records were different in the official histories (正史) and the local treatises (地 方志). As documented in Lu and Li (2013), the contemporary officials and intellectuals in China were aware of the transit of Venus.…”