| Project/Area Number |
17540223
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Astronomy
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| Research Institution | National Astronomical Observatory of Japan |
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Principal Investigator |
SOMA Mitsuru National Astronomical Observatory of Japan, Division of Optical and Infrared Astronomy, Asistent Professor, 光赤外研究部, 主任研究員 (30187885)
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| Co-Investigator(Kenkyū-buntansha) |
TANIKAWA Kiyotaka National Astronomical Observatory of Japan, Division of Theoretical Astronomy, Associate Professor, 理論研究部, 助教授 (80125210)
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| Project Period (FY) |
2005 – 2006
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| Project Status |
Completed (Fiscal Year 2006)
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| Budget Amount *help |
¥2,900,000 (Direct Cost: ¥2,900,000)
Fiscal Year 2006: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2005: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Keywords | Historical Astronomy / Earth Rotation / Solar Eclipses / Ephemerides / Lunar Tidal Term / Occultations |
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| Research Abstract |
Our research started when we found that the first solar eclipse of the year 628 recorded in the Japanese Annals (Nihongi or Nihon-shoki in Japanese) was actually the total solar eclipse as recorded. We proved this fact by comparing the record with contemporary solar eclipses in the years 616 and 702 recorded in China and the lunar occultation of Mars in the year 681 recorded in Japan. Former researchers had assumed that the record of 628 had been an exaggeration based on the smooth variation of the Earth's rotation velocity. Our finding suggested that the variation of the Earth's rotation speed was not uniform, and led us to the investigation when the abrupt changes of the Earth's rotation speed occurred in the past.
We developed a new method in which we can obtain simultaneously the Earth's rotation angle parameter value Delta-T and the tidal term in the Moon's longitude using ancient contemporary solar eclipses. The current tidal term had been obtained from the recent precise laser ranging measurements of the lunar distance, but the constancy of the term from the past had not been confirmed. We proved that the lunar tidal term has been almost constant from the year 200 BC using the solar eclipses recorded from 198 BC in China, Japan, and Rome. In order to obtain the Delta-T values we investigated all the total and annular solar eclipse records from the year AD 1 up to AD 1200 and found that the Delta-T value changed abruptly between the years 454 and 616 by more than 3000 sec, and between 873 and 912 by more than 600 sec, whereas the Delta-T value was almost constant between the years 616 and 873.
In addition, we collected ancient lunar eclipse timing records which will serve an important role to determine the past Delta-T values precisely.
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