共查询到20条相似文献，搜索用时 281 毫秒
1.
B. P. Kondratyev 《Astronomy Reports》2018,62(8):542-550
It is known from observations of the gravitational field and figure of the Moon that its center of mass (COM) does not coincide with its geometric center, with the line connecting these two points deviating to the Southeast of the direction toward the center of the Earth. The deviation of the lunar COM to the South was explained earlier. Here, the deviation of the lunar COMto the East of the direction toward the Earth is considered. The theory of the optical libration of a satellite orbiting synchronously about a planet for an observer at the secondary (free) focus of the orbit is first refined. It is shown that the main axis of inertia of the satellite undergoes asymmetric, non-linear oscillations whose amplitude is proportional to the square of the orbital eccentricity. A mechanism for the evolution of the orbit has been developed, taking into account the preferred direction of the axis of inertia of the Moon toward the empty focus. Of two alternative scenarios—evolution of the lunar orbit with decreasing or increasing eccentricity—only the latter scenario is consistent with the observed eastward shift of the lunar COM. This mechanism predicts that the lunar orbit had a lower eccentricity in the past than it does today. This conclusion is consistent with the results of observations and also with the fact that the eccentricity of the Moon’s orbit is indeed currently increasing, indicating that it was lower in the past than its current value, e = 0.0549. It is shown by averaging themotion over a rapid variable that thismechanismfor the orbital evolution can explain about 18% of the currently known eastward shift of the lunar COM. The results obtained refine the theory of the tidal evolution of the Moon. 相似文献
2.
B. P. Kondratyev 《Astronomy Reports》2018,62(10):705-712
It is known that the center of mass (CM) of the Moon does not coincide with its geometrical center of figure (CF), and that the CF–CMline deviates to the Southeast of the direction toward the center of the Earth. An investigation of this phenomenon, which has remained incompletely understood, has been carried out in two stages. One mechanism can explain part of the eastward shift of the lunar CM as being due to tidal evolution of the lunar orbit. A second mechanism is considered here, which relates this shift of the lunar CM with evolution of the shape of the Moon. A differential equation describing the shift of the lunar CMto the East in the course of the physically inevitable rounding of its shape as it moves away from the Earth is derived and solved. This mechanism not only explains the eastward shift of the lunar CM, but also predicts that the oblateness of the Moon could have been appreciable at earlier epochs, reaching values ε ≈ 0.31. The theory of figures of equilibrium in a tidal gravitational field is used to determine how close to the Earth the Moon could have formed. 相似文献
3.
Thermal inertia (I) is an important parameter in the Earth’s thermal study. There is no doubt that correct and up-to-date knowledge of thermal inertia particularly as it is affected by the land use/cover will provide good and useful information to agriculturists and environmental scientists. In this work, thermal inertia of Abeokuta City of Ogun State, southwestern Nigeria, was determined. Map of the study area was gridded using 2-min resolution which gave 5 × 5 sampling points from where core samples were collected. Bulk density (ρ s ), thermal conductivity (λ s ), and heat capacity (C s ) of the samples were determined. The pattern of variation of the city view of I (in the order of ×103 Jm?2 s?1/2 K?1) showed that the main urban built-up part of the study area, Abeokuta South, had the highest I mean, 0.76160 with standard deviation of 0.032547 and standard error of 0.01455541. The trend also varied along each sampling latitudinal line. It ranges between 0.509 and 0.756 on latitude 7° 14′, 0.557 and 0.768 on latitude 7° 12′, 0.642 and 0.782 on latitude 7° 10′, 0.7 and 0.794 on latitude 7° 08′, and between 0.642 and 0.728 on latitude 7° 06′. Hence, we have estimated thermal inertia of Abeokuta using the thermophysical properties of the study area. Thermal inertia tends to gradually decrease with distance from the city center (Abeokuta South). This result is promising in possible future consideration of urban ground heat energy conversion to other forms of energy. 相似文献
4.
现浇X形桩是为了提高单位混凝土承载力性能而开发的一种新型桩,异形横截面在确保桩周周长的前提下,能有效地减少混凝土用量;但目前针对异形横截面对水平向承载力特性影响方面的研究相对较少。基于X形横截面的3个控制参数：外包圆直径、开弧间距和开弧弧度,建立任意方向轴惯性矩控制方程,并分析X形横截面3个控制参数对截面轴惯性矩的影响规律。最后,提出控制截面面积或周长情况下X形截面惯性矩的最优化设计方案。研究结果表明,X形截面惯性矩随着开弧角度、开弧间距的减小而增大,随着外包圆直径的增大而增大。因此,在等混凝土材料用量或者控制桩周长情况下,适当增大外包圆直径、减小开弧角度和开弧间距有利于提高X形截面轴惯性矩,从而提高X形桩整体水平向承载力。 相似文献
5.
以2003年的中国第2次北极科学考察的海冰物理过程调查数据为依据,分析了海冰动力学特征并给出体现动力学特征的定量参数。这些参数指出:现场调查的海冰密集度同NOAA冰图上的密集度相比低2~3成,而厚度比1999年的中国首次北极考察结果减少2 m;冰层底面起伏方差约是冰层表面积雪起伏方差的3.8倍;浮冰最快以1 300m/h速度运动并伴随振荡旋转。实测浮冰向东北运动时,旋转角度增加,最大达到37.8o,东南方向旋转时,角度减小;浮冰运动的振荡周期为12.45 h,同该纬度惯性流振荡周期一致,体现出惯性流对浮冰运动的贡献。 相似文献
6.
It is proved that the projection of a triaxial ellipsoid with rectilinear meridians orthogonal to the rectilinear equator cannot be strictly conformal. The proof is based on the fact that due to the degeneration of the horizontal coordinate in latitude the relation between arc differentials in the projection depends linearly on the relation between the latitude and longitude differentials, but due to the dependence of the vertical coordinate on both latitude and longitude, the direction and certain value of this relation is retained upon the integration path selection. Other directions do not keep the relation between differentials of the corresponding arcs in the triaxial ellipsoid and in the projection plane. A projection keeping the angle between the parallel and the meridian obtained by the integration path selection by the initial meridian and then by the parallel is offered. 相似文献
7.
Petrova N. K. Nefedyev Yu. A. Zagidullin A. A. Andreev A. O. 《Astronomy Reports》2018,62(12):1021-1025
A brief review of modern observational achievements and the theoretical basis of physical libration of the Moon is presented. Special attention is given to the inferred existence of a lunar core and determination of its parameters. The creation of a theory of physical libration of the Moon, which requires analyses of semi-empirical series of long-term laser observations and the use of the highly accurate DE421 dynamical ephemeris, is related to this. A large role in this area has been played by the analytical theory of physical libration of the Moon constructed by Yu.V. Barkin, which made it possible for the first time to derive parameters of the free nutation of the lunar core from observations. This paper is based on a talk given at the conference “Modern Astrometry 2017,” dedicated to the memory of K.V. Kuimov (Sternberg Astronomical Institute, Moscow State University, October 23–25, 2017).
相似文献8.
V. V. Ivashkin 《Journal of Earth System Science》2005,114(6):613-618
The Moon-to-Earth low energy trajectories of ‘detour’ type are found and studied within the frame of the Moon-Earth-Sun-particle
system. These trajectories use a passive flight to the Earth from an initial elliptic selenocentric orbit with a high aposelenium.
The Earth perturbation increases the particle selenocentric energy from a negative value first to zero and then to a positive
one and therefore leads to a passive escape of the particle motion from the Moon attraction near the translunar libration
pointL
2. This results in the particle flight to a distance of about 1.5 million km from the Earth where the Sun gravitation decreases
the particle orbit perigee distance to a small value that leads to the particle approaching the Earth vicinity in about 100
days of the flight. A set of the Moon-to-Earth ‘detour’ trajectories is defined numerically. Characteristics of these trajectories
are presented. The ‘detour’ trajectories give essential economy of energy (about 150 m/s in Delta V) relative to the usual
ones. 相似文献
9.
Zagidullin A. A. Usanin V. S. Petrova N. K. Nefedyev Yu. A. Andreev A. O. Gudkova T. V. 《Astronomy Reports》2020,64(12):1093-1106
Astronomy Reports - The work is devoted to the study of the physical libration of the Moon. Interest in the traditional topic related to the rotation of the Moon is stirred up by the activity of... 相似文献
10.
S. A. Gasanov 《Astronomy Reports》2012,56(6):469-482
Steady-state solutions for the motion of a passively gravitating globular cluster (GC) inside an inhomogeneous, rotating, ellipsoidal elliptical galaxy (EG) are considered. It is assumed that an EG with a halo is comprised of a triaxial ellipsoid consisting of two layers. The first is formed by an inner, uniform ellipsoid representing the luminous part of the galaxy, while the second corresponds to the space between an inner and outer ellipsoid, which is uniformly filled with dark matter. The triaxial ellipsoids are taken to be homothetic and to have a common center; the space between them is called a homeoid. The outer boundary of the homeoid is the boundary of the galaxy halo. The densities of the luminous part of the EG and the homeoid are different. This picture of an EG is in agreement with our current understanding of galactic structure. The motion of the GC occurs outside the luminous part of the EG, but inside the homeoid, which is treated like a perturbing body. Steady-state solutions (libration points) are found for the GC, and its Lyapunov stability determined. The elliptical galaxies NGC 4472 (M49), NGC 4636, and NGC 4374, which contain a large number of GCs, are used as examples. Analysis of these galaxies shows that the exact expression for the potential of the luminous part of the EG must be used to find the libration points and study their stability, rather than an approximate expression for this potential. 相似文献
11.
Relationship between the velocity ellipsoids of galactic-disk stars and their ages and metallicities
The dependences of the velocity ellipsoids of F-G stars of the thin disk of the Galaxy on their ages and metallicities are
analyzed based on the new version of the Geneva-Copenhagen Catalog. The age dependences of the major, middle, and minor axes
of the ellipsoids, and also of the dispersion of the total residual velocity, obey power laws with indices 0.25, 0.29, 0.32,
and 0.27 (with uncertainties ±0.02). Due to the presence of thick-disk objects, the analogous indices for all nearby stars
are about a factor of 1.5 larger. Attempts to explain such values are usually based on modeling relaxation processes in the
Galactic disk. Elimination of stars in the most numerous moving groups from the sample slightly reduces the corresponding
indices (0.22, 0.26, 0.27, and 0.24). Limiting the sample to stars within 60 pc of the Sun, so that the sample can be considered
to be complete, leaves both the velocity ellipsoids and their age dependences virtually unchanged. With increasing age, the
velocity ellipsoid increases in size and becomes appreciablymore spherical, turns toward the direction of the Galactic center,
and loses angular momentum. The shape of the velocity ellipsoid remains far from equilibrium. With increasing metallicity,
the velocity ellipsoid for stars of mixed age increases in size, displays a weak tendency to become more spherical, and turns
toward the direction of the Galactic center (with these changes occurring substantially more rapidly in the transition through
the metallicity [Fe/H]≈−0.25). Thus, the ellipsoid changes similarly to the way it does with age; however, with decreasing
metallicity, the rotational velocity about the Galactic center monotonically increases, rather than decreases (!). Moreover,
the power-law indices for the age dependences of the axes depend on the metallicity, and display a maximum near [Fe/H] ≈−0.1.
The age dependences of all the velocity-ellipsoid parameters for stars with equal metallicity are roughly the same. It is
proposed that the appearance of a metallicity dependence of the velocity ellipsoids for thin-disk stars, recorded from the
close to the Sun, is most likely due to the radial migration of stars. 相似文献
12.
华南早新元古代莲沱组地层磁倾角偏低研究及其古地理意义 总被引：1，自引：0，他引：1
华南莲沱组最新的年龄结果表明,其时代结束于715Ma,因此,准确确定莲沱组的古纬度对"雪球地球"的研究具有重要意义。通过对莲沱组红层进行等温剩磁各向异性研究,获得其磁倾角校正因子为0.8719,校正后的磁倾角为70.4°,对比热退磁实验测得的莲沱组磁倾角为67.8°,则其磁倾角偏低量为2.6°。通过校正前后的磁倾角分别计算古纬度,获得磁倾角偏低所引起的古纬度变化为3.9°±6°。通过对比华南与澳大利亚-东南极板块的720Ma古地理位置,发现这一时期冰碛岩从中纬度到赤道广泛分布,验证了当时的"雪球地球"环境。 相似文献
13.
V. M. Fedorov 《Moscow University Geology Bulletin》2007,62(4):234-243
An attempt has been undertaken to examine time series of volcanic and seismic events in a multidimensional reference system related to the parameters of the Earth’s orbital motion. Volcanic eruptions and strong (M > 5) earthquakes (a sample from the USGS/NEIC seismological database: Significant Worldwide Earthquakes) [18] were analyzed within the fields of the JPL Planetary and Lunar Ephemerides, (DE-406) astronomical indicators [19]: the Earth-Moon distance, Earth-Sun distance, ecliptic latitude of the Moon, and the differences between the geocentric longitudes of the Moon and Sun, Venus and Sun, and Mars and Sun. Distribution spectra were obtained and normalization was performed taking the nonuniform motion of celestial bodies into consideration, and the values of multidimensional diurnal probability were calculated. As a result, the statistically reliable drift in the distribution of geoevents was calculated relative to the duration of the intervals of multidimensional diurnal probability, which indicates distribution regions where more geoevents can take place during shorter intervals (and vice versa). Linear relationships between the multidimensional diurnal probability and diurnal probability of geoevents were found. All these results and the astronomic ephemerides were used as a base for computing the probabilities of volcanic and seismic activity of the Earth for the period of 2005–2007. The spatial structure of volcanic and seismic processes was examined, which allowed the revelation of probabilistic parameters of the spatiotemporal structure of Earth’s geodynamic activity and outlining an approximate algorithm for its monitoring. 相似文献
14.
月球的化学演化 总被引：2，自引：0，他引：2
月球是一个发生了化学分异的星球,它由月壳、月幔±一个小的金属月核组成。大量观察事实显示月球曾经有过岩浆洋,岩浆洋的结晶分异主导了月球的化学演化。目前主流观点认为,月球是在太阳系演化的早期,至少45亿年前,一个火星大小的星球,与即将完成原始吸积的地球胚胎发生偏心撞击,造成地球的熔融,形成岩浆洋,飞溅出来的物质迅速吸积形成绕地球运动的月球,并且在月球上形成了全球规模的岩浆洋,进而发生了结晶分异。,由于月球上没有海洋和板块俯冲,岩浆洋分异是其化学演化的主要途径。月球岩浆洋的80％～85％在大撞击后的100Ma内已经固化,这可能是由于月球体积小、表面没有大气包裹所致。月球极贫水,因此在岩浆结晶过程中斜长石首先结晶。斜长石由于密度小于玄武质岩浆而漂浮在岩浆洋的表层,橄榄石等密度大的矿物则堆积在岩浆洋的底部。随着结晶分异的进行,残余岩浆不断富集不相容元素,包括K、U等放射性元素;与此同时,密度较大的钛铁矿开始结晶,造成高钛堆晶岩密度大于其下的橄榄石堆晶岩的不稳定结构,进而发生月幔翻转,引发一系列岩浆活动,进而形成月球上特有的镁质系列、碱质系列等岩石。由于月球氧逸度较低,Eu主要以＋2价形式存在,因此斜长石高度富集Eu,相应地除高地斜长岩外,其他岩石均表现为Eu高度亏损的特点。与此同时,Re在低氧逸度下表现为强亲铁元素的特点,Re／Os在月球岩浆过程中不发生分异。月球的体积远小于地球,因而其演化时间远远短于地球,很多原始的分异被完整地保留下来。因此月球的化学演化是类地行星早期演化过程的“化石”,尽管与现代的地球存在较大差异,但是对于认识地球早期演化具有借鉴意义。 相似文献
15.
INTRoDUCTIoNTostudythefigureanddensityoftheearthisthebasicmissionofgravimetry.Themethodapplyingthetheoryofgravitypotentialfieldtostudytheearthfigurehassufficientlydeveloped,bycontrastwiththiscase,thesamemethodusedinthestudyoftheearthdensityisratherweak.Traditionalearthgravimetryisonintimatetermswiththetheoryoftheearthfigurebutseemstobecomeestrangedfromtheearthdensity.UndertheclassicalStokes'theoryandMolodensky'stheorythestudyontheearthfigurehasalwaysavoidedcon-sideringtheearthdensitydistr… 相似文献
16.
Lin-Sen Li 《Astronomy Reports》2016,60(4):420-424
The variation of the instantaneous rotational angular velocity of the rigid Earth in the lunar-solar gravitational field is studied. The formula is derived for variation of the instantaneous angular velocity of the rigid oblate Earth using the potential function from Euler’s dynamic equations. The theoretical results show that under the influence of the gravitational field of the Moon and the Sun the Earth instantaneous angular velocity varies with periodic terms, but without secular variations. Amplitudes of the periodic terms and their periods are calculated and discussed. 相似文献
17.
Perturbed, rotational-oscillational motions of the Earth induced by the gravitational torques exerted by the Sun and Moon are studied using a linear mechanical model for a viscoelastic rigid body. A tidal mechanism is identified for the excitation of polar oscillations, i.e., for oscillations of the angular-velocity vector specified in a fixed coordinate frame, attributed to the rotational-progressive motion of the barycenter of the Earth-Moon “binary planet” about the Sun. The main features of the oscillations remain stable and do not change considerably over time intervals significantly exceeding the precessional period of the Earth’s axis. A simple mathematical model containing two frequencies, namely, the Chandler and annual frequencies, is constructed using the methods of celestial mechanics. This model is adequate to the astrometric measurements performed by the International Earth Rotation Service (IERS). The parameters of the model are identified via least-squares fitting and a spectral analysis of the IERS data. Statistically valid interpolations of the data for time intervals covering from several months to 15–20 yr are obtained. High-accuracy forecasting of the polar motions for 0.5–1 yr and reasonably trustworthy forecasting for 1–3 yr demonstrated by observations over the last few years are presented for the first time. The results obtained are of theoretical interest for dynamical astronomy, geodynamics, and celestial mechanics, and are also important for astrometrical, navigational, and geophysical applications. 相似文献
18.
We consider the three-dimensional motion of a star inside an inhomogeneous, rotating, elliptical galaxy with a homothetic density distribution. The libration points inside a triaxial, rotating, inhomogeneous, gravitating ellipsoid are determined and their stability studied. We determine zero-velocity surfaces and regions of possible motion both inside and outside the galaxy. The motions are shown to be stable in the sense given by Hill. The obtained zero-velocity surfaces enable the construction of a Roche model for a galaxy in the form of either a triaxial ellipsoid or an oblate ellipsoid of rotation. 相似文献
19.
To determine the Earth's dynamics and their equations, which are crucial for Earth science research, this paper analyzes the interaction forces in the motion of a three-body system(namely, fixed, active, and passive points), based on the orbital motion. The mathematical derivation has been conducted strictly according to trigonometric functions with time and space as variables. In spatial transformation, related data items are simplified and replaced reasonably and necessarily according to the physical phenomenon to conduct derivations of planar to spatial transformation, through which the motion point has universal significance. Moreover, the polynomial equation for the dynamics has been obtained. Results indicate that the polynomial expression for the dynamics comprises the tidal force, the powerful mid-latitude Force(PML Force), and gravitation. Gravitation analysis shows that it is proportional to the dynamics quality, the size of the angular velocity of their deviation from the progenitor–paternal orbital plane's center position, and the square of the progenitor orbital plane's distance. However, it is inversely proportional to the distance of the paternal orbital plane and not related to another body's quality. Some past errors are addressed and some constructive conclusions are offered in the discussion of gravitation. 相似文献
20.
开合构造总体上可以表述为:地球膨胀为开,收缩为合;垂向上地球物质离心(地心)运动为开,向心运动为合;水平方向上地球物质相背运动为开,相向运动为合。从驱动机制角度,我们把以热力(热能)为主体驱动的上浮物质运动定义为开;将重力(势能)为主体驱动的下沉物质运动定义为合。因此,开与合是一个高度综合的概念,具有广阔的内涵,开合运动是联系一切地质运动和地质科学的纽带。开合运动具有同步统一性,即垂向的开在水平方向也表现为开;垂向开得强烈,水平方向同样开得强烈,反之亦然。地球刚形成时诸多开合构造是无序的,地球的旋转运动统领地球上所有物质、能量、运动和大大小小的各种开合构造于旋转运动中,并将它们调剂到有序状态。简言之开合构造体系是开合旋运动长期作用下形成的不同时期、不同层次、不同级别的开合旋回组成的动态平衡构造体系。本文总结了地球开合旋构造体系物质组成、结构构造特征和规律,建立了开合旋复杂构造体系简要模型。提出平衡体系的形成机制是开合旋运动遵循地球重力均衡准则、最小内能原理(结晶化)、几何淘汰生长(垂直地心生长)和物质均匀化四条自然演化规律,其中重力均衡准则是主导的。由于地质事件(构造运动)在破坏开合旋平衡体系的同时,经常直接或间接向体系内输入新能量,往往使新的旋回比老旋回的结构构造更符合地质演化的自然规律,于是使地球显得更强大而有活力。这一次又一次的地质事件(构造运动)是开合旋构造体系螺旋式向前发展的动因。本文最后用开合构造观点探讨了地球的形成和演化,分析了板块构造运动的动力学过程。 相似文献