Astronomical observations in the Sòng dynasty
In this study, we used the Chapter of Astronomy (Tiānwénzhì) in Sòngshǐ, mainly because it includes one of the richest sets of astronomical information among the chronicles of the Chinese dynasties. All the capitals in the Sòng era, where the observations were made, were located at latitudes between 30 and 35 N. This period (CE 960–1279) overlaps with the CE 993–994 event as well as the so-called Medieval Warm Period (MWP: 10 CE–14 CE).
Among historical records worldwide, Chinese chronicles are remarkable for their feasibility as scientific data. Keimatsu (1976) emphasizes the predominance of Chinese astronomical records because trained experts on astronomical observation made continuous observations at specified locations and took dated records of astronomical phenomena, often with detailed notes such as motions, shapes, and colors.
Thus, records in the Chinese official chronicles are regarded to be more objective than many other historical documents (Keimatsu 1976), but we should keep in mind that Chinese astronomical observations were also made for the purpose of “fortunetelling” for policy makers. For example,
On–March CE 1204 at night, red clouds (chìyún) appeared within white vapors, crossing the sky from the east to the west. After that, conflagrations occupied the country for eight days. Thus, astrologers regarded this as a symbol of fire. (Sòngshǐ, Five Elements II b, p. 1413)
The reason for their consistent observations is based on Chinese culture and the politics of dynasties. Astronomical phenomena were traditionally thought to be signs from the heavens to the emperors reflecting their politics (i.e., stated at Sòngshǐ, Astronomical I, p. 949, translated text available in Appendix 1).
In order to deliver those heavenly messages to emperors, especially those of the Sòng dynasty, two observatories were constructed both in the imperial palace and near the capital city, Kāifēng, until the Jìngkāng Incident in CE 1126 (original text available in Appendices 2, 3, and 4, Yabuuchi 1967). Owing to their political importance, astronomical observations were made even during wars.
There is anecdotal evidence indicating the degree of sophistication and consistency of the astronomical observations in China during this period. During the invasion of the Sòng dynasty by the Jīn from the north, the Jīn captured Kāifēng in CE 1126. They broke all the observational instruments except for the spherical astrolabes, which were brought to Bĕijīng and adjusted by 4° in order to point to Polaris, as the instruments were moved from Kāifēng (35 N) to Bĕijīng (39 N) (the original text is available in Appendices 5 and 6).
After the fall of Kāifēng, the Sòng dynasty escaped southward via Shāngqiū (1128), Yángzhōu (CE 1128), and finally to Línān, the modern Hángzhōu (CE 1129–1279) (Mote 1999). It was in CE 1143 that the Sòng dynasty began reconstructing astrolabes. However, even during the period between CE 1126 and 1143 (without the use of astrolabes), we find records of both auroras and sunspots. This suggests that the Sòng dynasty continued observation even in such a chaotic time and without specially designed instruments (original text available in Appendix 6). Of course, we still have to note that frequency and accuracy of these observations must have been influenced by the political climate and other unknown factors.
The Sòngshǐ includes descriptions of many kinds of phenomena observed in the sky. Since we are interested in the past solar activities, we searched for descriptions that could be regarded as records of sunspots or auroras. For this purpose, we used a search engine, Scripta Sinica (2014), (http://hanchi.ihp.cinica.edu.tw) provided by Academia Sinica in Taiwan (http://www.sinica.edu.tw) that incorporates all the text data. This allowed us to automatically flag sentences that included keywords such as “black spot (hēizǐ)” and “red vapor (chìqì),” which may refer to sunspots and red auroras, respectively. Once the sentences that include the keywords were picked up, we read corresponding parts of the original text to check whether they actually refer to sunspots or auroras. We also calculated the moon phase to determine the sky conditions for each date of observation.
Sunspots are described as black spots or black vapors in the sun or in terms such as “the sun was weak and without light” (Saito and Ozawa 1992). In the Astronomical Treatise of Sòngshǐ, these are categorized in the subsection of unusual phenomena in the sun. Since this period was long before the invention of telescopes, the observations were presumably made by the naked eye during sunrises/sunsets or through clouds.
Sunspot records are often accompanied with information about number, shape, and size. Examples are given as follows:
On 11 January CE 1077, in the sun were black spots (
) as large as plums. They disappeared on 22.
(Sòngshǐ, Astronomy, p. 1087)
On—June CE 1145, in the sun were black vapors (hēiqì) shifting back and forth. (Sòngshǐ, Astronomy, p. 1088)
The sizes are expressed by comparison with something tangible. In the above example, it was “as large as plums.” The other expressions of size included are peach, glass, hen’s egg, and duck’s egg. Although we usually think of peaches as larger than plums, we do not know the relative and absolute size indicated by these expressions.
Although the ancient Chinese did not know the physical nature of the phenomena, there are numbers of records that can be considered as the observations of auroras. For example, Keimatsu (1969a, b) and Saito and Ozawa (1992) showed that the word “vapor” is likely to indicate auroras. Keimatsu (1976) listed all the luminous phenomena seen at night and also discussed whether they correspond to auroras or not.
Similarly to Keimatsu, we assume that the records of luminous phenomena observed at night are potentially those of auroras. Therefore, we surveyed the words that refer to luminous phenomena, such as vapor, light, and cloud. In the Astronomical Treatise of Sòngshǐ, these are categorized in the subsection of clouds and vapors. From the list of the potential auroral candidates, we manually removed the following two types. The first are those without dates. Most of these are found in the chapters explaining how fortunetelling is performed, which includes conversations between the emperor and servants or sages. Therefore, they are unlikely to be the direct records of the observations. The second type includes those seen during the daytime. Some of the daytime phenomena are presumably the halo around the sun.
Records of auroral candidates often include information about their color, motion, and direction; length, shape, and number of their bands; and sometimes the location of the observation when it was not made in the capital city. Examples of auroral records are given as follows:
On 26 February CE 996 at night, in the west were eight long and short bands of pale-white vapors (cāngbáiqì) like comets. They gradually passed the Milky Way, entwined like patterned snakes. (Sòngshǐ, Astronomy, p. 1308)
21 August CE 1119, red clouds (chìyún) appear in the northeast direction running through 30 ways of white vapors (báiqì). (Sòngshǐ, Astronomy, p. 1314)
The color is described as white, red, blue, yellow, or their mixture. The colors may be associated with what traditional Chinese called the Wŭxíng or Five Elements, in which the world consisted of five elements, namely metal, fire, wood, soil, and water, which correspond with colors of white, red, green, yellow, and black, respectively. Their motion and direction are usually given by the eight points of the compass.
Sometimes, these descriptions include information about constellations, planets, or the moon accompanying the auroras. Their lengths are given in units of “chǐ” or “zhàng.” In the Sòng Era, 1 chǐ was equal to 30.72 cm and 1 zhàng was 10 chǐ (Tonami et al. 2006). At this moment, we do not know how the lengths expressed using these units correspond to what was actually seen in the sky.
The shape and number of bands are described only in some of the recorded events. The shapes are expressed in a figurative way, such as “like serpents” or “like silk textiles.”
Moon phase calculation
The moon phase is a trait of the sky that we can calculate accurately for historic dates. To do this, we referred to the 6000-year catalog of moon phases with Julian dates found at the NASA Eclipse website (http://eclipse.gsfc.nasa.gov/phase/phasecat.html). This catalog is based on an algorithm developed by Meeus (1998).