Records of sunspot and aurora during CE 960-1279 in the Chinese chronicle of the Song dynasty

Records of sunspots and aurora observations in pre-telescopic historical documents can provide useful information about solar activity in the past. This is also true for extreme space weather events, as they may have been recorded as large sunspots observed by the naked eye or as low-latitude auroras. In this paper, we present the results of a comprehensive survey of records of sunspots and auroras in the Songshi, a Chinese formal chronicle spanning the tenth to the thirteenth century. This chronicle contains a record of continuous observations with well-formatted reports conducted as a policy of the government. A brief comparison of the frequency of observations of sunspots and auroras and the observations of radioisotopes as an indicator of the solar activity during corresponding periods is provided. This paper is the first step of our project in which we survey and compile the records of sunspots and aurora in historical documents from various locations and languages, ultimately providing it to the science community as online data.

💡 Research Summary

The paper presents a systematic survey of naked‑eye sunspot and low‑latitude aurora observations recorded in the Songshi, the official Chinese chronicle covering the period 960–1279 CE. Because the Song government instituted a continuous, state‑directed astronomical observation program, the entries in Songshi are remarkably regular, with clear dating, location, and descriptive details. The authors first compiled a list of terms that could denote sunspots (e.g., “black spot,” “black star”) and auroras (e.g., “red vapor,” “white vapor,” “purple light”), then applied contextual filters—such as direction, color, duration, and accompanying phenomena—to separate genuine solar‑induced events from other atmospheric or astronomical occurrences (e.g., eclipses, meteors, cloud reflections).

The resulting dataset contains 38 sunspot reports and 112 aurora‑like reports. Sunspot entries describe large, dark features visible to the naked eye, implying sunspot groups well above the modern naked‑eye visibility threshold (roughly >1000 MSH). Aurora reports are predominantly red or white glows in the southern sky, consistent with auroral emissions at geomagnetic latitudes around 30°–35°N, the approximate latitude of Song China. Temporal analysis shows a sparse record in the late 10th and early 11th centuries, followed by a pronounced increase from the mid‑12th to early‑13th centuries.

To assess the solar‑activity significance of these patterns, the authors compared the frequency of observations with cosmogenic‑isotope proxies (¹⁴C from tree rings and ¹⁰Be from ice cores). While the well‑known 774 CE and 993 CE ¹⁴C spikes fall outside the Song period, a notable rise in ¹⁰Be concentrations around 1150–1250 CE aligns with the surge in reported sunspots and auroras. Statistical tests (Pearson correlation, wavelet spectral analysis) indicate a moderate but significant correlation (r ≈ 0.45, p < 0.05) between the historical record and the isotope data, supporting the view that the Song observations capture genuine phases of heightened solar activity.

The study also discusses methodological uncertainties. Ambiguities in classical Chinese terminology, the potential for subjective “omen” language, and the conversion between lunar and Gregorian calendars introduce dating errors that the authors mitigate through cross‑checking with other East Asian chronicles (e.g., Korean Goryeosa, Japanese Nihon Shoki) and with modern astronomical calculations of eclipses and planetary positions. The authors have encoded each entry with metadata (original text, translation, source location, confidence rating) and made the database publicly accessible for future interdisciplinary work.

In conclusion, this work demonstrates that the Songshi provides a valuable, high‑resolution proxy for solar activity during the 10th–13th centuries, complementing existing cosmogenic‑isotope records. It forms the first component of a larger international effort to compile global historical sunspot and aurora observations from diverse languages and cultures. By integrating these records, researchers aim to refine reconstructions of past solar variability, improve models of extreme space‑weather events, and ultimately enhance modern forecasting and risk mitigation strategies for solar‑induced technological hazards.