TIMING RECORDS OF ANCIENT LUNAR ECLIPSES IN CHINA AND LONG-TERM VARIATION OF THE EARTH'S SPIN SPEED

The Chinese ancient accounts of timing observations of 48 lunar eclipses and the secular variation of the Earth's spin speed are discussed. A series of ${\Delta}$T expressing the secular deceleration of the Earth's rotation was obtained. The average increase rate of length of the day is about 1.5 milliseconds per century.