摘要
本文通过对近几年来由古代天象记录推出的△T序列的收集和整理,得到一样本点较多,在三千年尺度内分布较匀的△T序列.月球轨道角加速度取(-25.3±1.2)~″/cy^2.在计时天象所得△T序列的基础上,求得自转最佳平均相对角加速度/ω=-(19.9±1.8)×10^(-11)/yr.非潮汐相对角加速度_(NT)/ω=(8.3±0.5)×10^(-11)/yr.并且没有发现非潮汐项在千年尺度下有显著变化.
Since 1960's, more ancient observations have been used to detect the secluar change in the Earth Rotation, such as Babylonia Observations, Arabic Observations, Chinese Observations and telescope observations from 17th to 19th century. Several researchers such as P. M. Muller, F. R. Stephenson, L. V. Morrison, R. R. Newton, Han Yah-ben, Li Zhi-sen and Lu Ci-yuan have contributed a lot in this field. But their data samples differ not only in the number and the kind of observation but also in the time span the sample covered, their results, of course, are different. Basing on their work, we expect to obtain more reliable value of earth accerleration by using their medium results ΔT and selecting proper value of lunar tidal acceleration . We get seven ΔT sets according to different authors and different kinds of Observation, see table 2. By sorting out the data, the number of some ΔT set is cut down. It can be seen in table 3. Each set adopted different value of , i. e. they set up on different time scale. If we want to combine them into one series, we must give ΔT a correction: ΔT_((new))=ΔT_((old))-1/2(_(new)-_(old))T^2/0.508, T denote time in Julian Centuries from epoch 1790 year. We adopt _(new)=(-25.3±1.2)″/cy^2, which is wordly accepted as a reliable value recently. Then, we get a new ΔT series ranging from 708 B. C. to A. D. 1985, by combining the seven ΔT sets on the same time scale. Using least square fitting method, treating each ΔT value as equal weight, we can get a quadratic curve: ΔT_(fit)=a+bT+cT^2 from ΔT series. =-2c, /ω=0.634c(10^(-11)yr^(-1)), c(s/cy^2). The Earth Tidal Acceleration _T=53.5, non-tidal acceleration _(NT)=-_T. If we choice different ΔT set combination, we can get different new ΔT series. Comparing their standard error (EM) of least square fit, we get a best ΔT series which EM is minimum. See table 4. From the best ΔT series, we get /ω=(-19.9±1.8)×10^(-11)/yr, _(NT)/ω=(8.3±0.5)×10^(-11)/yr. We divide the best ΔT series into two part according to time span: -700 to 500; 500 to 1985. From the fiting results of two part ΔT series in table 6, we can see that the value of /ω in the two time span has no dramatic change, though its error change dramatically. This result is quite different from that of Stephenson.
出处
《天文学报》
CSCD
北大核心
1989年第3期315-322,共8页
Acta Astronomica Sinica
