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1993-05-03
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PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109. TELEPHONE (818) 354-5011
FOR IMMEDIATE RELEASE
Analyzing ancient Chinese accounts of solar
eclipses up to nearly 4,000 years old, Jet Propulsion
Laboratory researchers have determined to within a few
thousandths of a second the rate at which the Earth's daily
rotation has been gradually slowing down.
Their results -- from examining Chinese reports of
eclipses in the years 532 A.D., 899 B.C. and 1876 B.C. --
closely match previous studies.
They showed that the span of each day was shorter
by about 22/1,000ths of a second in 532 A.D., 42/1,000th
second in 899 B.C. and 70/1,000th second in 1876 B.C.
The study, due for publication in the British
journal Vistas in Astronomy, was authored by JPL astronomer
Kevin D. Pang, Kevin Yau of the University of Durham,
England, Hung-hsiang Chou of UCLA and Robert Wolff, a former
JPL staff member now with Apple Computer Inc.
Previously, other astronomers had analyzed accounts
of solar eclipses from Arabian and Babylonian sources for
historical evidence of the gradual slowing of the Earth's
rotation.
The oldest of those Middle Eastern solar eclipse
reports analyzed dated to about 700 B.C. Key gaps in the
Arabian and Babylonian records occurred during the Middle
Ages.
Dr. Pang and his colleagues turned to a formidable
1.2-million-word collection of ancient Chinese astronomical
records currently being prepared for publication by the
Beijing Observatory.
The Chinese text contains records of thousands of
eclipses extending back almost unbroken to the 19th century
B.C.
In order for an eclipse record to be useful, Pang
said, the time of the eclipse must be accurately known.
Since ancient accounts generally do not specificy
time of day, Pang explained that he and his colleagues
limited themselves to eclipses which occurred at sunrise or
sunset. The time of sunrise or sunset can be computed
retroactively.
One of the eclipses they focused on took place on
November 13 of the year 532 A.D., when China was divided into
separate northern and southern kingdoms. From historical
records it appears that sunrise took place during a solar
eclipse as observed from Loyang, the capital of the then
northern Wei kingdom.
A second eclipse studied by the team occurred on
April 21 of 899 B.C., when historical accounts relate that
the day "dawned twice" at the since-vanished city of Zheng. A
very similar "double sunrise" will occur over Helsinki,
Finland, on July 22, 1990.
Finally, the researchers were able to extend their
analysis back in time another 1,000 years -- far more ancient
than any other eclipse study -- by examining records of a
solar eclipse which occurred on October 16 of 1876 B.C.,
according to another report published recently by Pang in the
Journal of Hydrology.
Continued analysis of such ancient eclipse records
is expected to refine our understanding of the history of
rotation of the Earth, Pang said.
The JPL research is funded by NASA's Office of
Space Science and Applications.
#####
9-21-88 FOD
#1208