高精度测定外行星位置—可行性及实验

大行星位置的测量是天体测量学中的一项长期而重要的任务,如何在当前形势下高精度测定行星的位置是本文研究方向的最终目标,鉴于太阳系内行星和木星都有新技术进行高精度的位置观测,作者探讨了如何用光学手段高精度测量外行星（土星,天王星和海王星）的位置。提出了长焦距望远镜ＣＣＤ观测行星卫星和用中天望远镜ＣＣＤ观测暗恒星相配合的思路,因此,对长焦距望远镜ＣＣＤ观测外行星卫星和中天望远镜ＣＣＤ相对观测恒星进行了系     

天然卫星CCD精确定位的最新进展

天然卫星CCD精确定位观测对于宇宙飞船探测外行星、行星物理的研究以及天文参考系的连接等方面都有重要的意义．文章介绍了长焦距望远镜CCD观测天然卫星所遇到的各种困难以及解决问题的方案．重点评介了CCD图像处理和归算方法．最后,介绍了影响天然卫星位置测量精度的各种因素及最新观测结果的精度．     

天王星卫星CCD（SRT）位置测量的数字图象处理

天然卫星的位置测量在天体测量和天体力学中都有重要意义。国外有人对天王星卫星位置测量应用新的图象处理方法得到了高精度的卫星观测资料。利用云南天文台１米望远镜上获得的两颗卫星的ＳＲＴ的ＣＣＤ观测资料进行了新老图象处理方法的比较研究。当用两颗卫星直接作定标测量ＣＣＤ的比例尺和指向时表明：主星晕的处理对卫星位置的测量非常重要。去晕处理后,测得的比例尺和指向的弥散将大为减少。     

天王星卫星CCD观测的初步分析

１９９５ 年８ 月在上海天文台利用安装在１ ．５６ 米望远镜上的ＣＣＤ 探测器对天王星五颗主要卫星进行了定位试观测。将观测所得的位置资料与其理论值做了比较。结果表明：ＣＣＤ观测的位置精度优于照相观测的结果。这些资料对于卫星轨道的研究是有价值的。     

土星卫星CCD定位观测的初步分析

发表了１９９４年８月土星主要卫星ＣＣＤ观测的相对位置资料及其与理论值的比较分析。观测使用了开放实验室分山基地的１５６ｃｍ天体测量望远镜上的ＣＣＤ探测器．对观测资料的分析表明；Ｒｈｅａ和Ｄｉｏｎｅ相对于Ｔｉｔａｎ的位置精度为０．１２”。这相当于距离土星７００ｋｍ．土星卫星ＣＣＤ观测与最佳的照相观测比较，其位置精度相当。     

大行星位置测定的现状

大行星位置的测定是天体测量和天体力学中一项长期而重要的任务。本文介绍了测定大行星位置的意义,重点概括了大行星位置测定的现状,最后讨论了高精度测定外行星位置的困难及今后努力的方向。     

大行星位置测定的现状

大行星位置的测定是天体测量和天体力学中一项长期而重要的任务。本文介绍了测定大行星位置的意义,重点概括了大行星位置测定的现状,最后讨论了高精度测定外行星位置的困难及今后努力的方向。     

STEP天体测量误差源分析

系外类地行星空间探测计划(Search for Terrestrial Exo-Planets,以下简称"STEP")采用天体测量法和微像素级焦平面定标测量技术,设计望远镜焦平面检测精度达到1μas.在假定焦平面设计能达到检测精度的前提条件下,系统分析了恒星自行、视差、卫星速度和位置、光学系统的光心等关键因素对检测系外行星的影响.有别于传统的窄视场照相底片常数法,提出了一种恒星相对角距测量方法,以检测由于可能存在的系外行星而引起星对角距变化的非线性项,消除了传统窄视场天体测量中参考星位置和自行精度对检测系外行星的直接影响.针对同一天区内的8颗参考星和1颗具有行星系统的待测星,分别模拟出5 yr内的观测数据,利用最小二乘法进行处理,发现基于STEP自身1μas的观测精度,在这种情况下是可以观测到类地行星的.     

天王星卫星位置可视化软件设计

为了满足大行星卫星的高精度CCD位置观测与运动理论研究工作的需要 ,采用天王星 5颗主要卫星摄动理论模型 (Gust86 )作为核心 ,设计了一个天王星视位置可视化软件。该软件具有卫星证认 ,最佳观测时段选取 ,精确模拟卫星视运动和实时引导CCD精密定位观测等功能。     

天王星卫星的CCD观测与分析解的比对

本文给出了处理天王星卫星ＣＣＤ图象位置资料的新方法,并将我们在１９９５年取得的重要资料与两种理论模型位置进行了比较计算,结果表明经处理后的天王星五颗主要卫星ＣＣＤ观测精度有了较大提高。     

On the origin of the solar system and the exceptional position of the Sun in the Galaxy

The solar system's position in the Galaxy is an exclusive one, since the Sun is close to the corotation circle, which is the place where the angular velocity of the galactic differential rotation is equal to that of density waves displaying as spiral arms. Each galaxy contains only one corotation circle; therefore, it is an exceptional place. In the Galaxy, the deviation of the Sun from the corotation is very small — it is equal to ΔR/R _⊙≈0.03, where ΔR=R _c ?R _⊙,R _c is the corotation distance from the galactic center andR _⊙ is the Sun's distance from the galactic center. The special conditions of the Sun's position in the Galaxy explain the origin of the fundamental cosmogony timescalesT ₁≈4.6×10⁹ yr,T ₂?10⁸ yr,T ₃?10⁶ yr detected by the radioactive decay of various nuclides. The timescaleT ₁ (the solar system's ‘lifetime’) is the protosolar cloud lifetime in a space between the galactic spiral arms. The timescaleT ₂ is the presolar cloud lifetime in a spiral arm.T ₃ is a timescale of hydrodynamical processes of a cloud-wave interaction. The possibility of the natural explanation of the cosmogony timescales by the unified process (on condition that the Sun is near the state of corotation) can become an argument in favour of the fact that the nearness to the corotation is necessary for the formation of systems similar to the Solar system. If the special position of the Sun is not incidental, then the corotation circles of our Galaxy, as well as those of other galaxies, are just regions where situations similar to ours are likely to be found.     

Perturbations by the oblateness of the Earth and by the planets in the motion of the Moon

Perturbations in the motion of the Moon are computed for the effect by the oblateness of the Earth and for the indirect effect of planets. Based on Delaunay's analytical solution of the main problem, the computations are performed by a method of Fourier series operation. The effect of the oblateness of the Earth is obtained to the second order, partly adopting an analytical evaluation. Both in longitude and latitude are found a few terms whose coefficient differs from the current lunar ephemeris based on Brown's theory by about 0.01. While, concerning the indirect effect of planets, several periodic terms in the current ephemeris seem to have errors reaching 0.05.As for the secular variations of and due to the figure of the Earth and the indirect effect of planets, the newly-computed values agree within 1/cy with Brown's results reduced to the same values of the parameters. Further, the accelerations in the mean longitude, and caused by the secular changes in the eccentricity of the Earth's orbite and in the obliquity of the ecliptic are obtained. The comparison with Brown shows an agreement within 0.3/cy² for the former cause and 0.02/cy² for the latter. An error is found in the argument of the principal term for the perturbations due to the ecliptic motion in the current ephemeris.Proceedings of the Conference on Analytical Methods and Ephemerides: Theory and Observations of the Moon and Planets. Facultés universitaires Notre Dame de la Paix, Namur, Belgium, 28–31 July, 1980.     

On the model of the accumulation of the moon compatible with the data on the composition and the age of lunar rocks

It is suggested that the overall early melting of the lunar surface is not necessary for the explanation of facts and that the structure of highlands is more complicated than a solidified anorthositic ‘plot’. The early heating of the interior of the Moon up to 1000K is really needed for the subsequent thermal history with the maximum melting 3.5 × 10⁹ yr ago, to give the observed ages for mare basalts. This may be considered as an indication that the Moon during the accumulation retained a portion of its gravitational energy converted into heat, which may occur only at rapid processes. A rapid (t < 10³ yr) accretion of the Moon from the circumterrestrial swarm of small particles would give necessary temperature, but it is not compatible with the characteristic time 10⁸ yr of the replenishment of this swarm which is the same as the time-scale of the accumulation of the Earth. It is shown that there were conditions in the circumterrestial swarm for the formation at a first stage of a few large protomoons. Their number and position is evaluated from the simple formal laws of the growth of satellites in the vicinity of a planet. Such ‘systems’ of protomoons are compared with the observed multiple systems, and the conclusion is reached that there could have been not more than 2–3 large protomoons with the Earth. The tidal evolution of protomoon orbits was short not only for the present value of the tidal phase-lag but also for a considerably smaller value. The coalescence of protomoons into a single Moon had to occur before the formation of the observed relief on the Moon. If we accept the age 3.9 × 10⁹ yr for the excavation of the Imbrium basin and ascribe the latter to the impact of an Earth satellite, this collision had to be roughly at 30R, whereR is the radius of the Earth, because the Moon at that time had to be somewhere at this distance. Therefore, the protomoons had to be orbiting inside 20–25R, and their coalescence had to occur more than 4.0x10⁹ yr ago. The energy release at coalescence is equivalent to several hundred degrees and even 1000 K. The process is very rapid (of the order of one hour). Therefore, the model is valid for the initial conditions of the Moon.     

On the theory of the oblateness of the Sun

In this paper we first emphasize why it is important to know the successive zonal harmonics of the Sun's figure with high accuracy: mainly fundamental astrometry, helioseismology, planetary motions and relativistic effects. Then we briefly comment why the Sun appears oblate, going back to primitive definitions in order to underline some discrepancies in theories and to emphasize again the relevant hypotheses. We propose a new theoretical approach entirely based on an expansion in terms of Legendre's functions, including the differential rotation of the Sun at the surface. This permits linking the two first spherical harmonic coefficients (J ₂ and J ₄) with the geometric parameters that can be measured on the Sun (equatorial and polar radii). We emphasize the difficulties in inferring gravitational oblateness from visual measurements of the geometric oblateness, and more generally a dynamical flattening. Results are given for different observed rotational laws. It is shown that the surface oblateness is surely upper bounded by 11 milliarcsecond. As a consequence of the observed surface and sub-surface differential rotation laws, we deduce a measure of the two first gravitational harmonics, the quadrupole and the octopole moment of the Sun: J ₂=−(6.13±2.52)×10⁻⁷ if all observed data are taken into account, and respectively, J ₂=−(6.84±3.75)×10⁻⁷ if only sunspot data are considered, and J ₂=−(3.49±1.86)×10⁻⁷ in the case of helioseismic data alone. The value deduced from all available data for the octopole is: J ₄=(2.8±2.1)×10⁻¹². These values are compared to some others found in the literature. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005238718479     

Accounting for the viscosity of the fluid core in the problem of the physical libration of the moon

A two-component theoretical model of the physical libration of the Moon in longitude is constructed with account taken of the viscosity of the core. In the new version, a hydrodynamic problem of motion of a fluid filling a solid rotating shell is solved. It is found that surfaces of equal angular velocity are spherical, and a velocity field of the fluid core of the Moon is described by elementary functions. A distribution of the internal pressure in the core is found. An angular momentum exchange between the fluid core and solid mantle is described by a third-order differential equation with a right-hand side. The roots of a characteristic equation are studied and the stability of rotation is proved. A libration angle as a function of time is found using the derived solution of the differential equation. Limiting cases of infinitely large and infinitely small viscosity are considered and an effect of lag of a libration phase from a phase of action of an external moment of forces is ascertained. This makes it possible to estimate the viscosity and sizes of the lunar fluid core from data of observations.     

On some problems concerning the calculation of the form of the magnetopause and the electric field on the magnetopause in the framework of the continuum medium model

In order to understand the reason of the existence of the electric field in the magnetosphere, and for the theoretical evaluation of its value, it is necessary to find the solution of the problem of determination of the magnetosphere boundary form in the frameworks of the continuum medium model which takes into account part of the magnetospheric plasma movement in supporting the magnetospheric boundary equilibrium. A number of problems for finding the distribution of the pressure, the density, the magnetic field and the electric field on the particular tangential discontinuity is considered in the case when the form of discontinuity is set (the direct problem) and a number of problems for finding the form of the discontinuity and the distribution of the above-mentioned physical quantities on the discontinuity is considered when the law of the change of the external pressure along the boundary is set (for example, with the help of the approximate Newton equation). The problem which is considered here, which deals with the calculation of the boundary form and with the calculation of the distribution of the corresponding physical quantities on the discontinuity of the 1st kind for the compressible fluid with the magnetic field with field lines which are perpendicular to the plane of the flow in question, concerns the last sort of problems. The comparison of the results of the calculation with the data in the equatorial cross-section of the magnetosphere demonstrates that the calculated form of the boundary, the value of the velocity of the return flow and the value of the electric field on the magnetopause, agree satisfactorily with the observational data.