Verification of Sunrise and Solar Eclipse Times stated in theChongxiu-Daming Calendar
Go-Eun Choia,b, Ki-Won Leec, Byeong-Hee Mihna,baKorea University of Science and Technology, 217, Gajeong-ro, Yuseong-gu, Daejeon 34113, Republic of Korea(eun19831@kasi.re.kr)
bKorea Astronomy and Space Science Institute, 776, Daedeok-daero, Yuseong-gu,Daejeon 34055, Republic of Korea
cDaegu Catholic University, 13-13, Hayang-ro, Hayang-eup, Gyeongsan 38430, Republic of Korea

1. Introduction
The Chongxiu-Damingli 重修大明曆 (Greatly Revised Enlightenment Calendar1, hereafter GRE calendar) wasused in the Jin 金 dynasty (AD 1115–1234). This calendar was developed by Zhao, Zhi-Wei 趙知微 in 1171 bygreatly revising the Damingli 大明曆 compiled by Yang, Ji 楊級 of the same dynasty in 1127; and it wascontinued in the subsequent dynasty, the Yuan 元 dynasty (AD 1271–1368), before the enforcement of theShoushili 授時曆 (Seasons-Granting Calendar) in 1281 (Lee 1996).
It is known that the GRE calendar was a source for the Qitai calendar incorporated in the Zīj-i Īlkhānī, a Persian
astronomical handbook compiled by Nasīr al-Dīn Tūsī in 1272 (Isahaya 2013). In Korea, the GRE calendar wasused in the Joseon 朝鮮 dynasty (AD 1392–1910) since the reign of King Sejeong 世宗 (AD 1418–1450) tosupplement the calculations of solar and lunar eclipse times by the Chiljeongsan-Naepyeon 七政算內篇 (InnerParts for the Calculations of the Sun, Moon, and Five Planets, hereafter Naepyeon), a Korean calendar, together
with the Chiljeongsan-Oepyeon 七政算外篇 (Outer Parts for the Calculations of the Sun, Moon, and FivePlanets, hereafter Oepyeon), a Chinese-Islamic calendar.
This study aims to verify the sunrise and solar eclipse times by the GRE calendar, which have received littleattention from astronomical societies, based on the Jeongmyoyeon-Gyeosik-Garyeong 丁卯年交食假令(Example Supplement for the Calculation of the Solar and Lunar Eclipses that Occurred in 1447, hereafter
Garyeong). However, in this study, we will not discuss the calculation methods of the GRE calendar and themodern calculation methods in detail, as they will be published elsewhere (Choi et al. 2018). Instead, we introduce
the main results with the historical literature associated with the GRE calendar.

2. Historical literature
In China, the main contents of the GRE calendar are recorded in the astronomical chapter of the Jinshi 金史(History of the Jin Dynasty). The calendar was published as a book, in addition to the Garyong of the GREcalendar in Korea. Both Korean books are currently preserved in the Kyujanggak 奎章閣 Institute for KoreanStudies (see Figure 1). The GRE calendar consists of seven chapters: Qishuo 氣朔 (Solar Term and New Moon),
Guahou 卦候 (Hexagram and Seasons), Richan 日躔 (Solar Motion), Guilou 晷漏 (Sundial and Water Clock),
1In this study, the Chinese term li is translated as “calendar” as per astronomy conventions; however, a more appropriate

translation for modern concepts would be “system” (Sivin 2009). That is, Greatly Revised Enlightenment System andSeasons-Granting System.

Yuechan 月躔 (Lunar Motion), Jiaohui 交會 (Eclipses), and Wuxing 五星 (Five Planets). In Appendix A, welist the entire contents of the Garyeong, which we have referred to in this study.

(a)
(b)
(c)
Figure 1. Historical literature associated with the GRE calendar: (a) Jinshi (source: National Library of Korea),(b) the GRE calendar of Korean edition (source: Kyujanggak Institute for Korean Studies), and (c) the Garyeong(source: Kyujanggak Institute for Korean Studies).

3. Sunrise times
According to the preface of the astronomical chapter of the Jinshi, the GRE calendar was designed based on theJiyuanli 纪元曆 (Epoch Calendar) of the Northern Song 北宋 dynasty (AD 1127–1279). In order to verify thetruth of the records, we reproduced the sunrise and sunset times by the GRE calendar and compared them withresults of modern calculations using the astronomical algorithms of Meeus (1998) and the DE405 ephemeris ofStandish et al. (1996). For the observation sites, we assumed the historical capitals of the dynasties that used thecalendar including Luoyang 洛陽, which was an Old Chinese capital before the Northern Song dynasty. Table 1
lists the historical capitals assumed in this study.
Table 1. Historical capitals assumed in this study for estimating the observation site of sunrise and sunset times
in the GRE calendar.

CapitalLongitude

Latitude

NoteHarbin 哈爾濱126° 57 ʹ E

45° 32ʹ NJin dynasty (1115–1127)

Beijing 北京

116° 25 ʹ E

40° 15ʹ N

Jin dynasty (1128–1234)

Kaifeng 開封

114° 18 ʹ E

34° 19ʹ N

Northern Song dynasty (960–1127)

Hanyang 漢陽

126° 59 ʹ E

37° 37ʹ N

Joseon dynasty (1392–1910)

Luoyang 洛陽

112° 27 ʹ E

34° 40ʹ N

Old Chinese dynasties (BC 771 – AD 589)

For the direct comparison of sunrise and sunset times between the GRE calendar and modern calculations, we
obtained the daily daytime length (i.e., the period from sunrise to sunset) as it does not require the time conversion
between the apparent solar time of the past and the mean solar time of the present (refer to Lee et al. 2011). Figure
2 shows the differences in the daily daytime length between the GRE calendar and modern calculations for eachcapital. For a quantitative comparison, we determined the mean absolute difference (MAD) of the daily daytime
length between the GRE calendar and the modern calculations. We found that the sunrise and sunset times of theGRE calendar are more suitable at Kaifeng rather than those at Harbin or Beijing, i.e., MAD values are 5.58, 15.54

or 37.98 min, respectively, although the MAD value shows the minimum at Luoyang (i.e., 4.44 min). Therefore,
we believe that this fact supports the record of the Jinshi that the GRE calendar was compiled based on the Jiyuanliof the Northern Song dynasty.

Figure 2. Differences in the daily daytime length between the GRE calendar and modern calculations. The
horizontal axis represents the number of days since the winter solstice in 1170 (i.e., December 15). The verticalaxis represents the differences for the assumed capitals in units of minutes: Harbin (black solid), Beijing (magentadotted), Kaifeng (red short-dashed), Hanyang (blue long-dotted), and Luoyang (green dot and short-dashed).

4. Solar eclipse times
In the Garyeong, the calculation of the times of the solar eclipse that occurred on 10 September 1447 is explained
as an example (see also Mihn et al. 2014). We verified the calculation procedure of the solar eclipse times andcompared them with modern calculations. We used the observation site as Hanyang in the modern calculations tocompare the times with other calendars such as the Naepyeon, although the sunrise and sunset times show good
agreement at Kaifeng. In Figure 3, we present the diagram of the solar eclipse that occurred on 10 September 1447
using Besselian elements (e.g., Lee 2008). We used a ∆T value (difference between the terrestrial and universaltimes) of 4.25 min (Morrison and Stephenson 2004). According to our calculations, this partial eclipse began at
17 h 19 min and ended at 19 h 21 min in units of KST (Korean Standard Time, i.e., UT+9 h) at Hanyang. On theother hand, the greatest eclipse (18 h 23 min) occurred just before the sunset time (18 h 35 min).
In Table 2, we summarized the times of the solar eclipse for three stages—Chukui 初虧 (first external contact),
Shiji 食旣 (greatest eclipse), and Fuyuan 復圓 (last external contact) —for the GRE calendar, Naepyeon, andOepyeon together with the times from modern calculations. In the table, columns 2, 3, 4, 5, and 6 (i.e., A, B, C,D, and E) are eclipse times from the Gyosilkchubobeob-Garyong 交食推步法假令 (Example Supplement forCalculation Method for Solar and Lunar Eclipses, hereafter Chubobeob), Naepyeon, Oepyeon, the GRE calendar,
and modern calculations, respectively. Column 7, 8, 9, and 10 (i.e., A–E, B–E, C–E, and D–E) are the differencesof the times with modern calculations. The Chubobeob was compiled by Yi, Sunji 李純之 and Kim, Seok-Je
金石梯 in 1458 and its contents are basically same as the Garyeong of the Naepyeon, but they use slightly
different constant values and formulae (Hahn and Lee 2012). As is evident from Table 2, the GRE calendar shows
the smallest difference in the greatest eclipse time (i.e., ~1.2 min) but relatively large differences in the first andlast external contact times (i.e., ~33 min).

Figure 3. Diagram of the solar eclipse that occurred on 10 September 1447. The blue dashed, green dotted, andred solid lines represent eclipse magnitudes of 0.3, 0.5, and 0.7, respectively.
Table 2. Summary of the times of the solar eclipse that occurred on 10 September 1447.
AB

CD

E

A–E

B–E

C–E

D–Ehminhminhminhminhminminminminmin

P116

33.91606.7

1650.51650.91653.3

−19.4

−46.6

−2.8

−32.4

GE

1756.91728.81753.2

1753.1

1756.3

+0.6

−27.5

−3.1

−1.2

P4

1919.91850.91855.91929.3

18

55.3

+24.6

−4.4

+0.6

+34.0

1P1, GE, and P4 stand for first external contact, greatest eclipse, and last external contact, respectively.
2A, B, C, D, and E are eclipse times from the Chubobeob (Hahn and Lee 2012), Naepyeon (Lee 2007, Hahn et al. 2016),

Oepyeon (Ahn 2007), the GRE calendar, and modern calculations (this study), respectively.

It is unknown why the Joseon astronomer selected the solar eclipse of 1447 as an example. As mentioned above,the maximum of this eclipse occurred just before sunset at Hanyang. However, we think that this eclipse wasselected as it may a good example to calculate the magnitude at sunset or sunrise time, as its calculation method
is explained in the Garyeong. Based on the study for the solar eclipse of 1447, we developed the algorithm for thecalculation of solar eclipse times by the GRE calendar. To verify our algorithm, we compared the eclipse times
presented in the Yuanshi 元史 (History of the Yuan Dynasty). In the Yuanshi, the eclipse times by the GRE
calendar and Shoushili are recorded for 31 solar eclipses, with their observation times. As a first step, we compared
the greatest eclipse times for seven solar eclipses for the period from 1183 to 1277, and we found that the threeeclipses show differences of 1 Ke 刻 (~14.4 min). We believe that a detailed analysis of these differences isrequired, including the comparison for the first and last external contact times.

Acknowledgements
Ki-Won Lee is supported by National Research Foundation of Korea (NRF) grant funded by Korea government(MSIP) (No. 2016R1A2B4010887)

References
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Lee, K.-W., Ahn, Y. S., Yang, H.-J. 2011, Study on the system of night hours for decoding Korean astronomicalrecords of 1625-1787, Advances in Space Research, 48, 592-600
Meeus, J. 1998, Astronomical Algorithms, 2nd edition (Willmann-Bell, Inc.,Richmond)
Mihn, B.-H., Lee, K.-W., Ahn, Y. S. 2014, Analysis of interval constants in calendars affiliated with the Shoushili,
Research in Astronomy and Astrophysics, 14, 485-496
Morrison, L. V., Stephenson, F. R. 2004, Historical values of the Earth’s clock error ∆T and calculation ofeclipses, Journal of History and Astronomy, 35, 327-336
Sivin, N. 2009, Granting the Seasons: The Chinese Astronomical Reform of 1280, With a Study of Its Many
Dimensions and an Annotated Translation of Its Record (Springer, New York)Standish, E. M., Newhall, X. X., Williams, J. S., Folkner, W. F. 1997, JPL Planetary and Lunar Ephemeris (CDROM) (Willmann-Bell, Inc., Richmond)Appendix A. Contents of the Garyeong of the GRE calendar.
ContentsNote

求天正冬至

Qishuo 氣朔 (Solar Term and New Moon) chapter

求天正经朔
求弦望及次朔求经朔弦望入氣

Richan 日躔 (Solar Motion) chapter

求每日損益盈缩朓朒求经朔弦望入氣朓朒定數
求每日出入晨昏半晝分Guilou 晷漏 (Sundial and Water Clock) chapter

求經朔弦望入轉

Yuechan 月躔 (Lunar Motion) chapter

求朔弦望入轉朓朒定數
求朔望定日
求朔望入交

Jiaohui 交會 (Eclipses) chapter

求朔‧望加時入交常日及定日
求朔‧望加時入交常日及定日
求人交陰陽曆前後分
求日月蝕甚定餘
求日月食甚日行積度
求氣差
求刻差
求日食去前後定分
求日食分
求日食定用分求發斂1)

求日食所起
求日月出入带食所見分數
求冬至積度日度
求天正冬至加時黄道日度

2)

求日月食甚宿次
1)Guahou 卦候 (Hexagram and Seasons) chapter, 2)Richan 日躔(Solar Motion) chapter.