共查询到19条相似文献，搜索用时 281 毫秒
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中国传统星座中的紫微垣五帝内座和太微垣五帝座,都是古人为天上最高统治者天帝,在一年不同的五时处于不同方位处理政务而设的坐位。将五帝座作黄帝和四方之帝的坐位是“纬书”类的附会,与星座命名的本义相悖,由此造成不必要的混乱,一直延续至今,因此就有必要进行考证,给予澄清。 相似文献
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中国古代的星象划分
经过几千年的发展演化,中国古代形．成了一套完整的星象划分体系,是与西方星座划分体系完全不同的具有中国文化特色的星象划分体系。中国古代星象主要由“三垣二十八宿”所组成。三垣是指环绕北天极附近的三个星区,即紫微垣、太微垣和天市垣。每个星区都有东西两藩的星,左右环列,形如墙垣,故名之为“垣”。 相似文献
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春夏之交的傍晚,抬头仰望天空,在明亮的大角星(牧夫星座最亮星)与织女星之间,会看到一个近似半环形的小星座--"北冕座"。转过头来往南看,在人马座下方也有一个大约由10颗星星构成的环,比北冕座要暗一些,称为"南冕座"。这两个星座虽说不明亮,但是它们特有的美丽形象,常给人留下奇妙的想象。 相似文献
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船尾座船帆座罗盘座唧筒座○成怡然船尾座、船帆座、船底座和罗盘座在古希腊天文学家托勒密的４８个星座中均属于南船座。南船座是长达７２度的大星座。１７５１年法国天文学家拉卡伊将它分为４个星座：船尾座、船帆座、船底座和罗盘座（曾一度改称船桅座,现改回仍称罗盘... 相似文献
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雕具座天鸽座绘架座时钟座网罟座凤凰座＠成怡然雕具座天鸽座绘架座时钟座网罟座凤凰座成怡然当我们告别１９９７年迎来１９９８年的时候,我们已经漫游了６２个星座。还有分布在南半天球的２６个星座等待我们去巡视。不过,生活在北半球中纬度的读者是无缘一见的,生活在低纬度... 相似文献
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Pan Nai 《Chinese Astronomy and Astrophysics》1981,5(4):441-448
Records of observations of stars (including the determinatives of the 28 lunar mansions) have been collected and re-edited from five previous editions. After further consulting the star chart of XYXFY* and the Suzhou planisphere, we obtain the definitive positions of 360 stars which we can convert into the right ascensions and declinations for 1052 A.D., and hence their identification. Of the traditional 282 asterisms comprising 1464 stars, this list has 282 asterisms comprising 1457 stars, lacking only the star Shaocheng on the left Wall of the Purple Enclosure and the 6 stars of the asterism Ligong. With positions based on actual observations, this list embodies the traditional Chinese star system. It is the second listing after the “Star List of Master Shi” of the Warring Period, and provides an important and reliable reference for historical researches. 相似文献
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In this paper the tidal phenomena on the Earth are concisely specified, including solid tides, ocean tides and atmospheric tides due to the luni-solar tide-generating force, and the Earth pole tide due to the motion of the Earth's rotation axis (polar motion); as well as their effects on the Earth rotation. The outcomes of scientific researches of Chinese astronomers on these topics are described in some detail. These researches deal with the mechanisms responsible for tidal effects on the earth rotation, and on the measurements of the Earth rotation parameters. Finally, the effects discovered by Chinese researchers on the measurements of the period and change in period of pulsars are discussed. These effects are very small in magnitude but not negligible. 相似文献
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确定银河系的年龄是现代天体物理学的一项基本任务。其方法之一是核纪年法，即通过恒星中某一长寿命放射性元素的丰度随时间的变化来确定恒星的年龄，并以此作为银河系年龄的下限，其中目前的观测丰度来自恒星的光谱分析，恒星形成时的初始丰度来自理论模型的预言。这种方法最初是利用元素对Th／Nd来确定G矮星的年龄，近年来开始利用元素对Th／Eu和U／Th来确定晕族场星和球状星团内恒星的年龄。简要介绍了核纪年法确定银河系年龄的原理，回顾了恒星中Th和U的观测研究，其中着重介绍了极贫金属星的研究。详细讨论了用核纪年法估计银河系年龄的不确定性。作为与核纪年法的比较，简单介绍了确定银河系年龄的其他方法。提出了今后需要进一步研究的几项工作。 相似文献
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Non-linear equations governing the temporal evolution of the vector of instantaneous rotation are developed for an Earth with a homogeneous mantle having a viscoelastic Maxwell rheology and with a homogeneous inviscid fluid core.This general theory is investigated using the angular momentum theorem applied to the coupled core-mantle system. It allows to study the influence upon the planetary rotation of a quasi-rigid rotational motion in the liquid core. It also enables to investigate the consequences of excitation sources (e.g. pressure), located at the core-mantle interface. Especially, the influence of viscoelastic variations in the inertia tensors resulting from the rotation itself or from various excitation sources are detailed with the help of a Love number formalism. The equations of the linear theory for an elastic Earth with a liquid core, and the non-linear theory for a viscous planet with a quasi-fluid behavior are shown to be particular cases of our generalized system of equations. Some planetological applications may be derived from the quasi-fluid approximation. 相似文献
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Nikolay Sidorenkov 《Celestial Mechanics and Dynamical Astronomy》2003,87(1-2):27-38
Spectral analysis of the components of the relative atmospheric angular momentum vector is performed based on the series of these components for the 6 h intervals within the period of 1958–2000. These series have been computed in the Subbureau of the Atmospheric Angular Momentum of the International Earth Rotation Service using the NCEP/NCAR reanalysis of atmospheric observations. The basic harmonics of diurnal tides are determined. New results on the fortnight's and week's duration oscillations of the equatorial components of the atmospheric angular momentum are obtained. The zonal tides transformation mechanisms in the atmosphere are discussed. It is shown that the main mechanism of the zonal tides effect on the atmospheric variability is the amplitude modulation of daily oscillations of the relative atmospheric angular momentum. The effects of the atmospheric tides on the Earth rotation are discussed. 相似文献
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Estimates are made of the accuracy with which the brightness distributions across the disks of stars can be reconstructed
through analysis of data from high precision space-based photometry of classical eclipsing systems and observations of the
transit of planets across stellar disks. The ill-posed reconstruction problem was solved on a compact set of monotonically
nonincreasing, upwardly convex, non-negative functions. One of the difficulties with this method in the case of stars with
thin photospheres is the poor convergence of the solution at the point where the brightness distribution has a discontinuity
at the edge of the star's disk. Nevertheless, the use of this method for analysis of high precision observational data is
justified, since it can be used to obtain an estimate of the limb darkening that is independent of any model assumptions.
The reconstructed brightness distribution for the star HD 209458, for which the transit of a planet over its disk was observed
with the HST space telescope, is in good agreement with the results of a nonlinear model fit.
Translated from Astrofizika, Vol. 51, No. 4, pp. 595–606 (November 2008). 相似文献
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Fausto T. GrattonCharles J. Farrugia Laurence Bender 《Planetary and Space Science》2003,51(12):769-783
A MHD theory of combined Kelvin-Helmholtz (KH) and Rayleigh-Taylor (RT) instabilities for a transition layer with two different scale lengths (Δ and δ for the variation of velocity/magnetic fields and density, respectively) is presented. The study is motivated by reports of magnetopauses with no low latitude boundary layer, in which a sharp density drop over a distance δ?Δ is observed (“pristine” magnetopauses (J. Geophys. Res. 101 (1996) 49). The theory ignores compressibility effects and applies to subsonic regions of the dayside magnetopause. The RT effect is included to account for temporary periods of acceleration of the magnetopause, caused by sudden changes of the solar wind dynamic pressure. For small wavelengths λ, such that δ?λ?Δ, a WKB solution shows that the velocity gradient operates, together with magnetic tensions, to attenuate or even stabilize the Rayleigh-Taylor instability within a certain wavelength range. An exact dispersion relation for flute modes, valid for all λ, in the form of a fourth order polynomial for the complex frequency ω, is obtained from a model with a constant velocity gradient, dV/dy within Δ, and with δ→0. Flute modes are possible because of the existence of bands of very small magnetic shear on the dayside magnetopause (J. Geophys. Res. 103 (1998) 6703). The exact solution allows for a study of the change of the action of the velocity gradient with λ from the long-λ range where dV/dy is KH destabilizing to the short-λ range where dV/dy produces a stabilizing effect. Both, the WKB approximation and the well known tangential discontinuity model (Δ→0) are recovered as limiting cases of the exact solution. Properties of the KH and RT instabilities, for different density ratios on either side of the magnetopause, are described. For flute modes, at very small λ the RT instability grows faster and becomes the dominant effect. However, it is shown that the growth rate remains bounded at a finite value as λ→0, when a theory with a finite δ model is considered. To study configurations with finite, arbitrary, δ/Δ ratios, the MHD perturbation equations are solved numerically, using hyperbolic tangent functions for both the density and velocity transitions across the magnetopause. To examine the influence of different δ/Δ ratios on the growth rates of KH and RT, calculations are performed for different δ/Δ, with and without acceleration, and for two different density ratios. It is found that the general features exhibited by the constant dV/dy model, are confirmed by these numerical solutions. The stability of pristine magnetopauses, and the possibility of observing some theoretical predictions during magnetopause crossings in ongoing missions, are discussed. 相似文献
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G. A. Krasinsky 《Celestial Mechanics and Dynamical Astronomy》2002,84(1):27-55
Differential equations describing the tidal evolution of the earth's rotation and of the lunar orbital motion are presented in a simple close form. The equations differ in form for orbits fixed to the terrestrial equator and for orbits with the nodes precessing along the ecliptic due to solar perturbations. Analytical considerations show that if the contemporary lunar orbit were equatorial the evolution would develop from an unstable geosynchronous orbit of the period about 4.42 h (in the past) to a stable geosynchronous orbit of the period about 44.8 days (in the future). It is also demonstrated that at the contemporary epoch the orbital plane of the fictitious equatorial moon would be unstable in the Liapunov's sense, being asymptotically stable at early stages of the evolution. Evolution of the currently near-ecliptical lunar orbit and of the terrestrial rotation is traced backward in time by numerical integration of the evolutional equations. It is confirmed that about 1.8 billion years ago a critical phase of the evolution took place when the equatorial inclination of the moon reached small values and the moon was in a near vicinity of the earth. Before the critical epoch t
cr
two types of the evolution are possible, which at present cannot be unambiguously distinguished with the help of the purely dynamical considerations. In the scenario that seems to be the most realistic from the physical point of view, the evolution also has started from a geosynchronous equatorial lunar orbit of the period 4.19 h. At t < t
cr
the lunar orbit has been fixed to the precessing terrestrial equator by strong perturbations from the earth's flattening and by tidal effects; at the critical epoch the solar perturbations begin to dominate and transfer the moon to its contemporary near-ecliptical orbit which evolves now to the stable geosynchronous state. Probably this scenario is in favour of the Darwin's hypothesis about originating the moon by its separation from the earth. Too much short time scale of the evolution in this model might be enlarged if the dissipative Q factor had somewhat larger values in the past than in the present epoch. Values of the length of day and the length of month, estimated from paleontological data, are confronted with the results of the developed model. 相似文献