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1.
Calculation of meteoroid impacts on moon and earth 总被引：1，自引：0，他引：1
Concise derivations are given for the expected flux of meteoroids to the surfaces of the earth and the moon. Contrary to other published results, we find an accretion rate which is lower for the near side of the moon than for the far side and which is lower for the moon than for the earth, for all earth-moon distances. 相似文献
2.
Abstract— The purpose of this survey is to establish reference bulk elemental abundances for the eucrites and thereby provide the basis to test core formation models as well as partial melting, fractional crystallization and magma ocean theories for the eucrite parent body. In order to evaluate bulk elemental abundances for the eucrites, 296 peer-reviewed articles, monographs, theses or books and 143 abstracts dating from 1938 to 1997 were surveyed. Of the 101 eucrites having at least one set of elemental abundance analyses reported in the literature, 20 were selected for in-depth examination. The selection criteria of our sample were based on the total number of analyses available for a given eucrite and the total number of elements for which data exist. The mean bulk elemental abundance, 1σ standard deviation, and the percent deviation were calculated for each element in a given eucrite. In order to evaluate the quality of the mean abundances, the elements were then grouped according to availability of data and percent deviations. Possible reasons for the different deviations in the different groups are briefly discussed. From the major element abundances, the normative (CIPW) composition, the molar compositions of pyroxene, olivine and plagioclase, and the bulk densities were calculated and compared to petrographic observations. The calculated norms for the noncumulates agree well with the observations while the norms for the cumulates do not. Possible reasons for this are discussed. Unfortunately, analyses of many elements are poorly represented in the literature and many bulk analyses suffer from unacceptable levels of uncertainty. Therefore, future work requires bulk elemental analyses for some of the more poorly characterized elements in eucrites, especially those of key elements used for planetary modeling. 相似文献
3.
Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009 总被引：5，自引：0，他引：5
B. A. Archinal M. F. A��Hearn E. Bowell A. Conrad G. J. Consolmagno R. Courtin T. Fukushima D. Hestroffer J. L. Hilton G. A. Krasinsky G. Neumann J. Oberst P. K. Seidelmann P. Stooke D. J. Tholen P. C. Thomas I. P. Williams 《Celestial Mechanics and Dynamical Astronomy》2011,109(2):101-135
Every three years the IAU Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report takes into account the IAU Working Group for Planetary System Nomenclature (WGPSN) and the IAU Committee on Small Body Nomenclature (CSBN) definition of dwarf planets, introduces improved values for the pole and rotation rate of Mercury, returns the rotation rate of Jupiter to a previous value, introduces improved values for the rotation of five satellites of Saturn, and adds the equatorial radius of the Sun for comparison. It also adds or updates size and shape information for the Earth, Mars?? satellites Deimos and Phobos, the four Galilean satellites of Jupiter, and 22 satellites of Saturn. Pole, rotation, and size information has been added for the asteroids (21) Lutetia, (511) Davida, and (2867) ?teins. Pole and rotation information has been added for (2) Pallas and (21) Lutetia. Pole and rotation and mean radius information has been added for (1) Ceres. Pole information has been updated for (4) Vesta. The high precision realization for the pole and rotation rate of the Moon is updated. Alternative orientation models for Mars, Jupiter, and Saturn are noted. The Working Group also reaffirms that once an observable feature at a defined longitude is chosen, a longitude definition origin should not change except under unusual circumstances. It is also noted that alternative coordinate systems may exist for various (e.g. dynamical) purposes, but specific cartographic coordinate system information continues to be recommended for each body. The Working Group elaborates on its purpose, and also announces its plans to occasionally provide limited updates to its recommendations via its website, in order to address community needs for some updates more often than every 3 years. Brief recommendations are also made to the general planetary community regarding the need for controlled products, and improved or consensus rotation models for Mars, Jupiter, and Saturn. 相似文献
4.
该文基于标准化自协方差函数的组合算法计算了阿仑方差、哈达玛方差的重叠和非重叠形式以及改进阿仑方差、时间方差的等效自由度,并用经验公式计算了总方法估计的等效自由度,在此基础上对各种方差估计不同噪声情况下的等效自由度进行了比较分析,得出如下结论,总方法估计的等效自由度大于相应非总方法估计的等效自由度,重叠和非重叠阿仑方差估计的等效自由度大于相应哈达玛方差估计的等效自由度;对非重叠估计而言,噪声的频率越低,其等效自由度越大;而相应的重叠估计和总方法估计与之相反,噪声的频率越高,其等效自由度越大,这也说明重叠估计和相应的总方法估计对高频噪声等效自由度的提高优于低频噪声. 相似文献
5.
Sufficient conditions for escape and for retention in the three-body problem are derived which, for escape, are more stringent than those previously derived and, for retention, avoid the difficulty of containing the inverse of the mass of the escaping particle. 相似文献
6.
7.
D. J. Scheeres 《Celestial Mechanics and Dynamical Astronomy》2006,94(3):317-349
Equilibrium conditions for a mutually attracting general mass distribution and point mass are derived and their stability
computed. The equilibrium conditions can be reduced to six equations in six unknowns, plus the existence of four integrals
of motion consisting of the total angular momentum and energy of the system. The equilibrium conditions are further reduced
to two independent equations, and their theoretical properties are studied. We derive three distinct conditions for a relative
equilibrium which can be used to derive robust algorithms for solving these problems for non-symmetric gravity fields: a set
of necessary conditions, a set of sufficient conditions, and a set of necessary and sufficient conditions. Each of these conditions
is well suited for the computation of certain classes of equilibria. These equations are solved for non-symmetric gravity
fields of interest, using a real asteroid shape model for the general gravity fields. Explicit conditions for the spectral
and energetic stability of the resulting equilibria are also derived and computed for the shape of interest. 相似文献
8.
J. Rösch 《Solar physics》1985,96(2):213-217
The basic equations for measurement of solar diameters by means of the scanning heliometer are given, and the first processing of the rough data is described, either for oblateness evaluation, for medium term oscillations detection, or for investigation of secular diameter changes. 相似文献
9.
S. A. El Wakii M. S. Abdel Krim M. T. Attia A. A. El Ghazaly E. A. Saad 《Astrophysics and Space Science》1989,158(1):95-105
The slowing-down Boltzmann equation for generalized boundary conditions is considered and transformed to one-speed equation in Laplace space. Exact relations between energy reflection and transmission coefficients for a problem with diffuse reflecting boundary conditions and the albedos for the problem with isotropic boundary conditions are obtained. The Galerkin method is used to calculate the energy reflection coefficient for a finite slab for different thicknesses at different mass ratiosA, target to projectile mass, at different synthetic-scattering kernels. The results for partial heat fluxes for isotropic and anisotropic-scattering dispersive medium are given. The results obtained for isotropic boundary conditions are compared well with the exact results. 相似文献
10.
中高轨卫星广播星历精度分析 总被引：17，自引：0，他引：17
GPS广播星历参数具有物理意义明确、参数少、精度高等优点,可以考虑将它应用于其他卫星导航系统。但是GPS系统的卫星构成比较单一,而其他卫星导航系统可能包含中地球轨道 (MEO)、倾斜地球同步轨道(IGSO)和地球静止轨道(GEO)等多种不同类型的中高轨卫星。分析了采用GPS广播星历参数时,MEO、IGSO和GEO卫星的广播星历拟合精度,特别讨论了轨道倾角接近于0的GEO卫星的广播星历拟合精度,并给出了相应的改进措施。计算表明,对于 MEO卫星,2 h的广播星历拟合精度(三维位置)可达厘米级;对于IGSO卫星和轨道倾角较大的GEO卫星,4 h的广播星历拟合精度约为0．1 m,径向位置误差在厘米量级;而对于轨道倾角接近于0的GEO卫星,若不采取特殊措施,由于轨道倾角和升交点经度统计相关,其广播星历拟合精度很差,为此提出了一种坐标转换方法。采用此方法后的广播星历拟合精度可达0．1 m,径向位置误差为厘米量级。 相似文献
11.
For both asteroids and meteor streams, and also for comets, resonances play a major role for their orbital evolutions but on different time scales. For asteroids both mean motion resonances and secular resonances not only structure the phase space of regular orbits but are mainly at the origin for the inherent chaos of planet crosser objects.For comets and their chaotic routes temporary trapping into orbital resonances is a well known phenomenon. In addition for slow diffusion through the Kuiper belt resonances are the only candidates for originating a slow chaos.Like for asteroids, resonances with Jupiter play a major role for the orbital evolution of meteor streams. Crossing of separatrix like zones appears to be crucial for the formation of arcs and for the dissolution of streams. In particular the orbital inclination of a meteor stream appears to be a critical parameter for arc formation. Numerical results obtained in an other context show that the competition between the Poynting-Robertson drag and the gravitational interaction of grains near the 2/1 resonance might be very important in the long run for the structure of meteor streams. 相似文献
12.
M. Y&#;ld&#;z 《Monthly notices of the Royal Astronomical Society》2007,374(4):1264-1270
The α Centauri (α Cen) binary system is a well-known stellar system with very accurate observational constraints on the structure of its component stars. In addition to the classical non-seismic constraints, there are also seismic constraints for the interior models of α Cen A and B. These two types of constraint give very different values for the age of the system. While we obtain 8.9 Gyr for the age of the system from the non-seismic constraints, the seismic constraints imply that the age is about 5.6–5.9 Gyr. There may be observational or theoretical reasons for this discrepancy, which can be found by careful consideration of similar stars. The α Cen binary system, with its solar-type components, is also suitable for testing the stellar mass dependence of the mixing-length parameter for convection derived from the binaries of Hyades. The values of the mixing-length parameter for α Cen A and B are 2.10 and 1.90 for the non-seismic constraints. If we prioritize the seismic constraints, we obtain 1.64 and 1.91 for α Cen A and B, respectively. By taking into account these two contrasting cases for stellar mass dependence of the mixing-length parameter, we derive two expressions for its time dependence, which are also compatible with the mass dependence of the mixing-length parameter derived from the Hyades stars. For assessment, these expressions should be tested in other stellar systems and clusters. 相似文献
13.
Bharat Mahajan Srinivas R. Vadali Kyle T. Alfriend 《Celestial Mechanics and Dynamical Astronomy》2018,130(3):25
A novel approach for the exact Delaunay normalization of the perturbed Keplerian Hamiltonian with tesseral and sectorial spherical harmonics is presented in this work. It is shown that the exact solution for the Delaunay normalization can be reduced to quadratures by the application of Deprit’s Lie-transform-based perturbation method. Two different series representations of the quadratures, one in powers of the eccentricity and the other in powers of the ratio of the Earth’s angular velocity to the satellite’s mean motion, are derived. The latter series representation produces expressions for the short-period variations that are similar to those obtained from the conventional method of relegation. Alternatively, the quadratures can be evaluated numerically, resulting in more compact expressions for the short-period variations that are valid for an elliptic orbit with an arbitrary value of the eccentricity. Using the proposed methodology for the Delaunay normalization, generalized expressions for the short-period variations of the equinoctial orbital elements, valid for an arbitrary tesseral or sectorial harmonic, are derived. The result is a compact unified artificial satellite theory for the sub-synchronous and super-synchronous orbit regimes, which is nonsingular for the resonant orbits, and is closed-form in the eccentricity as well. The accuracy of the proposed theory is validated by comparison with numerical orbit propagations. 相似文献
14.
S. H. Zisk 《Earth, Moon, and Planets》1972,4(3-4):296-306
Radio interferometry is a new technique for the measurement of the surface topography of the Moon. Elevation data may be obtained directly without regard for unambiguously-identified features, for any lunar surface element that yields a recognizable radar echo.A program has been undertaken at the Haystack Observatory for the topographic mapping of the major part of the lunar Earthside hemisphere. Some results are presented for the Alphonsus-Arzachel region, showing evidence for a late lava flow of a viscosity and, hence, presumably a chemical composition, differing from that of near-by mare surfaces. 相似文献
15.
Robert D. Furber 《Celestial Mechanics and Dynamical Astronomy》2014,118(3):273-289
Accuracy measures are derived for the proper relative extrema in the separation distance function for co-periodic Kepler orbits. The conventional approach involves two numerical iterative processes: the method for solving Kepler’s equation for the eccentric anomaly, and the Newton–Raphson method for identifying times of the extrema. The sensitivity of the accuracy of the solution to the conditioning of the case is determined for stress tests including sequences of cases approaching a constant, then vanishing, separation. Invariance under interchanged satellite labels, single- and double-precision codes, and condition number estimates are compared to determine the number of justifiable digits. 相似文献
16.
Photoelectric observations of the two eclipsingvariables, were obtained in UBV standard system, for SWLac and, inVB standard system for OOAql.A new set of geometrical and physical elements for thesystems were obtained from both minima, through theirmagnitude variation during the observation time using themethod of: Fourier Analysis Techniques in-Frequency-domain for thelight curve changes. The two eclipsing variables are contact, the firstcontact angle was 48.1° for SW Lac and 47.7° for OO Aql.Absolute elements and effective temperatures of the twocomponents for both systems are derived. 相似文献
17.
Room temperature Mossbauer spectra have been obtained for several iron bearing phases in the octahedrite Toluca. The spectrum for kamacite contains six lines, as expected for a ferromagnetic material. That for taenite contains a strong six-line pattern, closely similar to that for kamacite, plus a weak singlet. The former is due to the ferromagnetic form of taenite, which predominates, and the latter to the non-equilibrium paramagnetic form. The spectra for troilite, schreibersite and cohenite are similar to those for terrestrial troilite, synthetic schreibersite and cementite, respectively. With some troilite samples, a weak doublet due to some non-magnetic phase was obtained. This was found to match the doublet reported for terrestrial pyrite, but the results are not such as to make a positive identification possible. This exploratory study of the Mossbauer spectra of some of the principal phases found in iron-nickel meteorites suggests that the main value of Mossbauer spectroscopy in the study of meteorites lies in its ability to detect relatively small amounts of paramagnetic phases such as the paramagnetic form of taenite. 相似文献
18.
《Planetary and Space Science》1987,35(1):79-90
The recent accurate analysis of the satellite 1965-14A at 15th-order resonance has allowed significantly improved solutions to be derived for the individual harmonic coefficients in the geopotential of order 15 and 30. For order 15, coefficients of degree 15–36 have been evaluated (Tables 3 and 5); for degree 15–23, the mean accuracy is equivalent to 0.6 cm in geoid height; but the accuracy is poorer for degree 24–36, averaging 2.4 cm. For order 30, only the coefficients of even degree, from 30 to 40, have been evaluated (Table 8): for degree 30 and 32 the accuracy is equivalent to 1 cm in geoid height, but deteriorates to 2 cm for higher degree. The accuracies for 15th order, though in need of improvement for high degree, are better than tl ose available for any other order, and are already of the standard required for achieving in the 1990s the very difficult goal of a comprehensive geoid accurate to 10cm. 相似文献
19.
Based on published data, we have compiled a catalogue of fundamental astrophysical parameters for 593 open clusters of the Galaxy. In particular, the catalogue provides the Galactic orbital elements for 500 clusters, the masses, central concentrations, and ellipticities for 424 clusters, the metallicities for 264 clusters, and the relative magnesium abundances for 56 clusters. We describe the sources of initial data and estimate the errors in the investigated parameters. The selection effects are discussed. The chemical and kinematical properties of the open clusters and field thin-disk stars are shown to differ. We provide evidence for the heterogeneity of the population of open star clusters. 相似文献
20.
F. Mignard 《Earth, Moon, and Planets》1980,23(2):185-201
We present here a model for the tidal evolution of an isolated two-body system. Equations are derived, including the dissipation in the planet as in the satellite, in a frequency dependent lag model. The set of differential equations obtained is still valid for large eccentricity, as well as for all inclinations. The reference plane chosen enables us to study the evolution for both the orbital plane and the equatorial plane.The results obtained show the Moon, after having approached the Earth with small variations for the inclination and the eccentricity, exhibits strong increase for the two parameters in the vicinity of the closest approach. In every case the eccentricity tends towards the value 1, whereas the variations of the in clinations are dependent on the magnitude of the dissipation in the satellite.Some qualitative results are also investigated for the final behaviour of satellites such as Triton and the Galilean satellites. 相似文献