利用中国古代月掩星资料研究地球自转速率长期变化的方法探索

我国古代有相当丰富的月掩星观测记录。因其未记录观测时刻，用它们来研究地球自转速率的长期变化是相当困难的。刘次沅率先引入“可见时间段”的概念，使这一问题的解决成为可能。本文对刘次沅所采用的进行了分析和评述，并在此基础上提出了“最或然二次曲线拟合法”以综合处理中国古代的月掩星资料，期望能得到较为客观、合理、精确的地球自转速率的长期变化值。     

地球自转长期变化的最新结果

地球自转长期变化的研究依赖于古代天象记录.近年来这方面研究取得明显进展.本文着重介绍作者由中国古代公元十世纪以前732个月掩犯记录得到的最新结果,并与其他结果进行了对比和综合分析,中国月掩犯记录填补了公元三至八世纪的资料缺环,并证实了公元五世纪前后地球自转非潮项的明显变化.     

中国古日食记录和地球自转长期变化

古代日月食观测记录是研究过去几千年地球自转长期变化的最有用的材料, 本文对文献记载的中国古代(明末以前)的日食观测作了分析讨论。指出,西汉以后资料是系统完整的。多为当时首都的观测记录。可惜的是,古人不重视记录天象发生的准确时刻。 作者从这些材料中筛选出13次观测地点明确的日全食观测,探讨分析了地球自转长期变化的趋势。     

地球自转长期变化非潮汐机制之一

地球自转的长期减慢一般归为日月潮汐摩擦,根据古代日月食的记载及珊瑚类生物生长线的研究,可估算地球自转慢为每世纪２．４ｍｓ左右的日长变化,但是,潮汐摩擦并不是减速的唯一机制,还要考虑其它非潮汐因素,本试图考虑太阳风和磁层的相互作用,分析地球磁层中的磁力线在背阳面,由于地球自转引起磁力线压缩与稀疏,产生附加磁压力而引起的力矩对地球自转长期变化的影响,结果表明：这一非潮汐变化机制引起的角加速度约为ｗ＝     

引力常数变化对地球自转长期变化的影响

探讨和估计了各种引力常数变化理论对地球角速度和日长变化的影响。各种引力常数变化理论包括了引力常数G随时间、空间以及速度变化等几个方面的影响。另外也估计了对地球自转角速度和日长变化产生的效应。其中有些研究对探讨地球自转变化也有启发意义。     

地球自转长期变化非潮汐机制之一

地球自转的长期减慢一般归为日月潮汐摩擦,根据古代日月食的记载及珊瑚类生物生长线的研究,可估算地球自转变慢为每世纪２．４ｍｓ左右的日长变化．但是,潮汐摩擦并不是减速的唯一机制,还要考虑其它非潮汐因素．本文试图考虑太阳风和磁层的相互作用,分析地球磁层中的磁力线在背阳面,由于地球自转引起磁力线压缩与稀疏,产生附加磁压力而引起的力矩对地球自转长期变化的影响．结果表明：这一非潮汐变化机制引起的角加速度约为ω＝－１．６１×１０－２２ｒａｄ／ｓ．     

月掩星预报

月球在天球上每小时大约向东移动半度,这样我们有时候就会看到它会遮挡住一些恒星或行星等天体,过段时间后,这些天体又会重新出现,这就是月掩星。对这些现象进行计时观测,得到的时间数据可以用来修正月球轨道精确数据、准确预测月球的运动、研究地球自转的不均匀性。     

掩星情报站

五月份最引人注目的天象莫过于月掩金星了,这次月掩金星在我国只有南方一小部分地区可见,其他地区可见不同程度的金星合月现象。小行星掩星适合观测的有四次,掩食时间最长的一次是2．9秒。被掩星最亮的为5等,而且掩食时间近3秒,是一次十分难得的机会。     

掩星情报站

我们最常见的掩星事件就是月掩恒星,行星虽然也在黄道附近运行,但我们经常看到的是行星合月,这种现象几乎每个月都能看到。月掩行星相对来说就比较少见,所以每次月掩行星时都会引起爱好者的格外关注,在2月份我国爱好者将会看到一次月掩木星的天象奇观。     

中国古代月食记录中的月亮位置分析

统计和分析了我国古代月食记录中的月亮位置。这些宿度记录主要集中在北魏、宋朝和清朝,这三个朝代正史中记录的月食宿度错误率分别是15%、5%和4%。清代之前的大部分月食宿度记录应该是实测的结果,清代正史月食宿度记载则来自预报记录。地方性月食宿度记录绝大部分出自明清的地方志,其中对宋朝和明朝的月食宿度记录比较多,错误率分别为21%和6%,清朝地方志交食记录中对当朝发生日月食时的日月位置的记录很少,而对清之前出现此类天象时的日月位置有较多的记载。1740年前后至清末月食的宿度记录精度比之前有所提高,其主要原因是《历象考成后编》和《仪象考成》的编纂。     

Secular Variation of Earth's Rotation: Inferred from the Chinese Ancient Shoushi Calendar (Ad 1281)

The Shoushi calendar (epoch of AD 1281, Yuan dynasty) is famous and very accurate in ancient China. It has evolved perfect and complete theoretical models of solar system objects, such as solar and lunar motions during that period. Almost every part of this work corresponds to the modern astronomical yearbooks. Compiled by native Chinese astronomers, it sums up through their studies many real observing results. The mathematical methods were adopted in this calendar before the foundation of Newton’s mechanical system. It is presented in this paper that the indirect system is also very useful to recover the real observing historical material. By selecting these calculating results, we may sum up the integral data of the secular variation of the Earth’s rotation from 1000 BC to AD 1500. This revised version was published online in July 2006 with corrections to the Cover Date.     

双星系中两子星的自转对双星轨道变化的后牛顿效应

本文利用解摄动方程的平均值法求得在PPN框架中二体自转对轨道要素产生的后牛顿效应的长期变化影响．利用这一理论对CWCep和DRVul两颗双星中两子星的自转对轨道近星点和平近点角的长期摄动的后牛顿效应做了计算。结果表明：对于两个质量较大快速自转的子星,由此所产生的后牛顿效应的摄动量是不能忽视的。     

An Interpretation of the Non-Tidal Secular Variation in the Earth Rotation: the Interaction Between the Solar Wind and the Earth's Magnetosphere

The long period variation of the earth rotation is generally explained by the tidal friction. The tidal friction, however, is not the only source to influence the earth rotation in long term. In this paper, by means of the interaction between the solar wind and the magnetosphere of the earth, the additional magnetic pressure will exist in the magnetic tail due to the crowding and sparseness of the magnetic lines in the consideration of the earth rotation, which could be considered as a source of effecting the long term variation of the earth rotation. It is shown in this paper that this mechanism can produce angular deceleration of the Earth rotation in the magnitude of ω = −1.7 × 10-22 s-2. This result might be a prompt to search for other sources in the secular variation of the rate of the Earth rotation variation further in order to regulate the observed result with the theoretical one. This revised version was published online in July 2006 with corrections to the Cover Date.     

Trends of sea level variations in the South China Sea from merged altimetry data

In this study, more than 13 yr of merged altimetry sea level anomalies (SLA) data were used to analyze the trends of sea level variations in the South China Sea (SCS). The result shows that the mean sea level over the SCS has a rise rate of 11.3 mm/yr during 1993–2000 and a fall rate of 11.8 mm/yr during 2001–2005. The geographical distribution of the sea level variations over the SCS is asymmetric with a pronounced variation existing in the deep water. The trends of thermosteric sea level variations were also examined using Ishii data and MITgcm assimilation data. The result indicates that the thermal change of the upper layer of the SCS has a significant contribution to the sea level variations. Heat budget analysis suggests that heat advection may be a key factor influencing the thermal change. Apart from thermal contribution, the effect of water exchange on the sea level variations was also studied.     

在后牛顿引力理论(PPN形式)中引力常数变化对地球自转产生的效应

介绍和论述了在后牛顿引力理论(PPN形式)中在优越参考系和非优越参考系中经过参数化后引力常数变化对地球自转产生的效应,其中特别重点介绍了年周期变化的效应。此外也将理论结果同观测结果相对比。     

液核地球自转速率变化的带谐潮效应Ⅱ--数值计算与比较

地球自转速率的潮汐变化可由无量纲参数k/cm)(k和cm分别为壳幔的有效Love数和有效极转动惯量)来表征。对于一个具有弹性地幔、平衡海潮和核幔不耦合的地球k/cm=0.944,且与潮波频率无关。海潮的非平衡扰动使k/cm为复数,且与频率有关。大气对自转速率有效勒夫数的贡献约为Δkat=0.0075。同时地幔滞弹性对勒夫数也产生扰动。利用本文得到的理论公式和最新的潮汐数据计算了地球自转速率的潮汐变化,及其有关地球物理机制的影响。     

液核地球自转速率变化的带谐潮效应Ⅰ--理论公式

根据液核地球动力学原理,重新推导了在日月子引潮力作用下的地球自转速率变化的理论公式,由此明确地引入了液核影响因子,它与地球和液核的极转动惯量的变化有关。不同于Yoder.C.F(1981)的理论,本文给出了基于引潮力位Doodson展开的地球自转速率变化、日长变化和世界时变化的理论公式,指出尺度因子的转动惯量应取为地幔的有效极转动惯量,Love数应取地幔的有效Love数的理由。     

The brightness of the helium D3 line in the undisturbed chromosphere from eclipse observations

Slitless spectra of the chromosphere, observed cinematographically at the total solar eclipse of 10 July 1972, were reduced. The surface brightness distribution of the helium D₃ line in the undisturbed chromosphere was obtained in agreement with results by other observers. The available eclipse data on the D₃ absolute brightness was analysed by means of theoretical curves of growth. Intensity data by some observers were found to be certainly too high. A trend was found that the D₃ absolute brightness in the quiet chromosphere decreases with the increasing solar activity (sunspot number). This perhaps indicates a variation of the spicule number over the solar surface during a sunspot cycle.