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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.
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
3.
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
4.
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
5.
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
6.
《Physics and Chemistry of the Earth, Part C: Solar, Terrestrial & Planetary Science》1999,24(4):359-363
Monthly quantiles of ionization parameters are important information for system planning and to assess one aspect of ionospheric variability. For ionosonde parameters the data base is probably large enough to allow mapping of deciles. For electron content the situation is not so good: at least for Europe the data base only allows to construct maps for the upper and and the lower monthly quartiles.We present mapping procedures and maps for monthly quartiles of electron content and of foF2 based on experiences with mapping procedures for monthly medians. It turned out that for the lower quartiles it is necessary to to use more coefficients for the quartile maps than for the median maps.We discuss possibilities to gain decile information for electron content from foF2. For a few selected months and locations deciles can be gained from the Faraday effect on the signals of geostationary satellites. These selected cases are used to check on procedures to use foF2 experience to construct electron content deciles. 相似文献
7.
Mohamed Adel Sharaf Mervat El-Sayed Awad Mona A. Banaja 《Astrophysics and Space Science》1987,133(2):339-353
In this paper, economical and stable recurrence formulae for the Earth's zonal potential and its gradient for the KS regularized theory will be established for any numberN of the zonal harmonic coefficient. A general recursive computational algorithm based on these formulae is also established for the initial value problem of the KS theory for the prediction of artificial satellites in the Earth's gravitational field with axial symmetry. Applications of the algorithm for the problem of the final state prediction are illustrated by numerical examples of three test orbits each for two geopotential models corresponding toN=2 andN=36. A final state of any desired accuracy is obtained for each case study, a result which shows the flexibility of the algorithm. 相似文献
8.
9.
Andrew J. Barber Peter A. Thomas H. M. P. Couchman C. J. Fluke 《Monthly notices of the Royal Astronomical Society》2000,319(1):267-288
We present the results of weak gravitational lensing statistics in four different cosmological N -body simulations. The data have been generated using an algorithm for the three-dimensional shear, which makes use of a variable softening facility for the N -body particle masses, and enables a physical interpretation for the large-scale structure to be made. Working in three dimensions also allows the correct use of the appropriate angular diameter distances.
Our results are presented on the basis of the filled-beam approximation in view of the variable particle softening scheme in our algorithm. The importance of the smoothness of matter in the Universe for the weak lensing results is discussed in some detail.
The low-density cosmology with a cosmological constant appears to give the broadest distributions for all the statistics computed for sources at high redshifts. In particular, the range in magnification values for this cosmology has implications for the determination of the cosmological parameters from high-redshift type Ia supernovae. The possibility of determining the density parameter from the non-Gaussianity in the probability distribution for the convergence is discussed. 相似文献
Our results are presented on the basis of the filled-beam approximation in view of the variable particle softening scheme in our algorithm. The importance of the smoothness of matter in the Universe for the weak lensing results is discussed in some detail.
The low-density cosmology with a cosmological constant appears to give the broadest distributions for all the statistics computed for sources at high redshifts. In particular, the range in magnification values for this cosmology has implications for the determination of the cosmological parameters from high-redshift type Ia supernovae. The possibility of determining the density parameter from the non-Gaussianity in the probability distribution for the convergence is discussed. 相似文献
10.
We present the computation of effective refractive coefficients for inhomogeneous two-component grains with three kinds of inclusions with m incl = 3.0 + 4.0i, 2.0 + 1.0i, 2.5 + 0.0001i and a matrix with mm = 1.33 + 0.01i for 11 volume fractions of inclusions from 0 to 50 per cent and wavelengths λ= 0.5 , 1.0, 2.0 and 5.0 μm. The coefficients of extinction for these grains have been computed using a discrete dipole approximation. Computation of the extinction by the same method for grains composed of a matrix material with randomly embedded inclusions has been carried out for different volume fractions of inclusions. A comparison of extinction coefficients obtained for both models of grain material allows one to choose the best mixing rule for a mixture. In cases of inclusions with m incl = 2.0 + 1.0i and 2.5 + 0.0001i the best fit for the whole wavelength range and volume fractions of inclusions from 0 to 50 per cent has been obtained for the Lichtenecker mixing rule. In the case of m incl = 3.0 + 4.0i the fit for the whole wavelength range and volume fractions of inclusions from 0 to 50 per cent is not very significant but the best fit has been obtained for the Hanai rule. For volume fractions of inclusions from 0 to 15 per cent a very good fit has been obtained for the whole wavelength range for Rayleigh and Maxwell-Garnett mixing rules. 相似文献
11.
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
12.
R. K. Varma 《Astrophysics and Space Science》1978,55(1):113-124
A theory for the interaction of a neutral gas with a moving magnetized plasma is given. The Alfvén expression for the critical velocity is identified with that for the terminal velocity while another expression for the threshold velocity for interaction is given. The implications of these results to the Alfvén-Arrhenius model for the solar system are discussed.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30 May, 1978. 相似文献
13.
In this paper, economical and stable recurrence formulae for the Earth's zonal potential and its gradient for Burdet's regularized theory will be established for any number N of the zonal harmonic coefficients. A general recursive computational algorithm based on these formulae is also established for the initial value problem of Burdet oscillator for the prediction of artificial satellites in the Earth's gravitational field with axial symmetry. Applications of the algorithm for the problem of the final state prediction are illustrated by numerical examples of three test orbits each for two geopotential models corresponding to N = 2 and N = 36.A final state of any desired accuracy is obtained for each case study, a result which shows the flexibility of the algorithm.Dept. of Astronomy, KAU 相似文献
14.
《New Astronomy》2021
The importance of some atom hydrogen collisions in AGN has been investigated. The results are useful for better estimation of the hydrogen Balmer lines fluxes, which usage for effective temperature diagnostics in astrophysical plasma is limited by errors from the line formation models. The data could be also useful for modeling cooler and denser parts of AGN BLR clouds, as well as for the investigation of Rydberg states of hydrogen and for the study of their influence during the cosmological recombination epoch. The results of the present work suggest that the investigated processes are of interest for the research and modeling of such media. 相似文献
15.
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
16.
An empirical formula for the cross section for inelastic hadronic interaction of antihelium with nuclei for the projectile energy range from 0.3 GeV/n to 80 GeV/n and target atomic mass number A from 4 to 120 has been developed. It is based on the available experimental data of nucleon (antinucleon) — nucleus and helium — nucleus inelastic cross sections. Such a formula is needed by experiments designed to search for antihelium in cosmic rays. With this formula one can estimate the efficiency of antihelium detection and correct for antihelium attenuation in the atmosphere for the balloon-borne experiments. A byproduct of this work is an empirical formula for antiproton-nucleus inelastic cross. 相似文献
17.
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
18.
The criterion for the secular stability of nuclear burning is revised for times shorter than the effective time of relaxation into diffusion.Using the Cattaneo equation for the heat flux, we show that before the establishment of steady state resistive flow, conditions for the stability of nuclear burning change of sign quasiperiodically, for any given value of the gravothermal specific heat. Implications of this result in calculations of nuclear fusion in accreting neutron star envelopes are suggested. 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.
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