共查询到20条相似文献，搜索用时 20 毫秒
1.
与国家天文台兴隆站2.16m安装的北京天文台暗天体分光成像仪(BAO Faint Object Spectrograph and Camera,BFOSC)系统相似,云南天文台2.4m望远镜安装了云南暗弱天体光谱及成像仪(Yunnan Faint-Object Spectrograph and Camera,YFOSC),对它在直接照相时的CCD平场性能做了测定.使用不同旋转角度拍摄平均而得的平场,可以使不同位置拍摄的像场,所受最大误差≤0.015 mag.但与卡焦的VersArray CCD照相机不同,即使在视场中间直径6.′5的圆内,误差约在0.010～0.013 mag之间,达不到≤0.005 mag的精度. 相似文献
2.
G. Horedt 《Astrophysics and Space Science》1975,35(1):L15-L16
3.
S. M. Chitre 《Journal of Astrophysics and Astronomy》2000,21(3-4):331-337
The interior of the Sun is not directly accessible to observations. Nonetheless, it is possible to infer the physical conditions
inside the Sun with the help of structure equations governing its equilibrium and with the powerful observational tools provided
by the neutrino fluxes and oscillation frequencies. The helioseismic data show that the internal constitution of the Sun can
be adequately represented by a standard solar model. It turns out that a cooler solar core is not a viable solution for the
measured deficit of neutrino fluxes, and the resolution of the solar neutrino puzzle should be sought in the realm of particle
physics. 相似文献
4.
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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The spiral waves in a model galaxy consisting of differentially rotating and non-rotating subsystems are considered on the basis of participating phenomena. The subsystems involved represent the Populations I and II of normal spirals, respectively. The spiral waves in such a systems are unstable in the Landau sense. Due to this instability they grow up to attain finite amplitude. This growth is stopped by a non-linear effect (the quasilinear effect), the steady state with waves of finite amplitude being established. The hypothesis is proposed that these waves should be identified with the spiral structure of the galaxies. 相似文献
7.
The effect of mass balance variations on changes in surface elevation of the Greenland ice sheet is examined in connection with the rise in sea level that will be caused by increased melting. Changes in surface elevation of several metres (of either sign) can occur in the ablation area of the ice sheet over a period of a few years as a result of random ablation forcing without being evidence of change in mean climate. Similar, but smaller, changes can occur in the accumulation area due to accumulation forcing. The ablation area of the ice sheet probably thickened from the mid-1970s to the mid-1980s as a result of lower ablation in that period but thinned again in the late 1980s as a result of higher ablation then. There is no evidence of any present trend of increased melting. Future climate warming will involve an accelerated thinning of the ablation area that could be detected in 1–2 decades against the background of natural fluctuations in surface elevation. 相似文献
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A.E. Ringwood 《Icarus》1976,28(3):325-349
Recent hypotheses of lunar evolution hold that the Moon was extensively or completely melted and differentiated about 4.6 b.y. ago, resulting in formation of the plagioclase-rich lunar highlands underlain by a great thickness of complementary ferromagnesian cumulates. Mare basalts are interpreted as being formed by subsequent remelting of these cumulates. These hypotheses are tested experimentally in the cases of several bulk compositions which have been proposed for the Moon—those of Taylor and Jakes, Ganapathy and Anders, Wänke and co-workers, and Anderson. An extensive experimental investigation of melting equilibria displayed by the Taylor-Jakes model at high pressures and temperatures is presented. This permits a quantitative evaluation of the manner in which a model Moon with this composition would crystallize and differentiate under conditions of (i) total melting throughout, and (ii) total melting only of an outer shell a few hundred kilometers thick. A detailed study is made of the capacity of the cumulates underlying the crust in these models to produce mare basalts by a second stage of partial melting. A wide range of experimentally based arguments is presented, showing that for both cases, partial melting of such cumulates would produce magmas with compositions quite unlike those of mare basalts. In order to minimize these difficulties, bulk lunar compositions containing substantially smaller abundances of involatile components (e.g. CaO, Al2O3, TiO2) relative to major components of intermediate volatility (e.g. MgO, SiO2, FeO) than are specified in the Taylor-Jakes model, appear to be required. Other bulk lunar composition models proposed by Ganapathy and Anders, Wänke and co-workers and Anderson, were similarly tested in the light of experimental data. All of these are far too rich in (Ca and Al) relative to (Mg + Si + Fe) to yield, after melting and differentiation, cumulates capable of being parental to mare basalts. Moreover these compositions, whdn melted and differentiated, appear incapable of matching the composition of the pyroxene component of the lunar highland crust.A brief discussion of the petrogenesis of mare basakts is presented. The most promising model is one in which only the outer few hundred kilometers of the Moon were melted and differentiated around 4.6 b.y. ago. Continued radioactive heating of the deep undifferentiated lunar interior provided a second generation of primitive magmas up to 1.5 b.y. after the early melting and differentiation. These primitive magmas participated in assimilative interactions with late-stage differentiates formed near the crust-mantle boundary during the 4.6 b.y. differentiation. These interactions might explain some trace element and isotopic characteristics of mare basalts. The model possesses some attractive characteristics relating to the thermal evolution of the Moon. 相似文献
10.
M. Moons 《Celestial Mechanics and Dynamical Astronomy》1984,34(1-4):263-273
A theory of the libration of the Moon, completely analytical with respect to the harmonic coefficients of the lunar gravity field, was recently built (Moons, 1982). The Lie transforms method was used to reduce the Hamiltonian of the main problem of the libration of the Moon and to produce the usual libration series p1, p2 and . This main problem takes into account the perturbations due to the Sun and the Earth on the rotation of a rigid Moon about its center of mass. In complement to this theory, we have now computed the planetary effects on the libration, the planetary terms being added to the mean Hamiltonian of the main problem before a last elimination of the angles. For the main problem, as well as for the planetary perturbations, the motion of the center of mass of the Moon is described by the ELP 2000 solution (Chapront and Chapront-Touze, 1983). 相似文献
11.
Charles F. Yoder 《Icarus》1979,40(3):341-344
The dynamic plausibility of various ideas on the origin of the Trojans is briefly discussed. We take the point of view that the present, tightly bound population has secularly evolved through some mechanism from less to more tightly bound orbit configurations. The mechanisms considered are changes in the Jovian mass or semimajor axis during planetary formation, collisional interactions with external, asteroidal material, and cometary outgassing. 相似文献
12.
D. L. Khokhlov 《Astrophysics and Space Science》2013,343(2):787-790
Constraints of the laboratory physics on the model of the universe are considered. The constraints are derived from the measurement procedure for the flux of electromagnetic radiation and valid for any model of the universe. In classical physics, an observer in the frame of the detector can measure the transformation (1+z)?1 for the energy flux of the electromagnetic wave emitted in the frame of the source but cannot any transformation for space and time between the frames of the source and detector. In quantum mechanics, the energy of the electromagnetic radiation as a function of the distance may be measured as a redshifted frequency of photon (1+z) or as a decrease of the intensity of radiation (1+z). 相似文献
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本文介绍了仪器上某些部套结构或配置的不当之处及其引起的一些不良现象,包括竖直轴系的过定位影响,高度慢动系统的结构不妥和升降电机的位置不当等问题,叙述了对这些部套修改和完善的方法以及取得的效果. 相似文献
15.
P. Nenovski 《Planetary and Space Science》1985,33(11):1313-1316
In the recent estimation by Maltsev and Lyatsky (1984) of the group velocity of surface waves on the inner boundary of the plasma sheet, the effect of the curvature of the field lines of the ambient magnetic field of the Earth on the spectrum has been assessed. The authors have not accounted for the fact, however, that the group velocity of the compressional surface magnetohydrodynamic waves itself is nonzero transverse to the magnetic field—a characteristic which has been omitted in the spectrum of Chen and Hasegawa (1974), being used by Maltsev and Lyatsky.This characteristic of compressional surface MHD waves is inherent for the spectrum , obtained by Nenovski (1978) in the cold plasma limit VA ? VS(VA is Alfvén velocity, and VS, sound velocity). A comment has been made on the restrictions, proceeding from the approximation, used by Maltsev and Lyatsky. The estimation of the velocities for movements of auroral riometer absorption bays have been reviewed. 相似文献
16.
利用全球卫星激光测距服务系统(ILRS,International Laser Ranging Service)标准点资料对Ajisai卫星进行精密定轨,残差均方根(RMS)优于3 cm,得到该星的精密轨道.进而对长春站40 cm空间碎片光电望远镜获得的Ajisai卫星的天文定位资料进行精度分析,外符合精度约3″左右.单独利用天文定位数据进行轨道改进,内符合精度优于3″.改进轨道的x、y、z坐标3分量在观测数据覆盖范围内的精度在100 m之内.同样地对Jason-1卫星作数据分析,结果和Ajisai卫星精度相当.分析各个弧段的精度变化,发现定标星个数减少,会导致天文定位精度下降.据此提出可以把最少定标星比例作为评定数据质量的参考指标之一. 相似文献
17.
Alessandro Morbidelli 《Celestial Mechanics and Dynamical Astronomy》1998,72(1-2):129-156
The present paper reviews our current understanding of the dynamical structure of the Kuiper belt and of the origin of Jupiter-family
comets. It also discusses the evolutionary scenarios that have been proposed so far to explain the observed structure of the
Kuiper belt population.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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Alexander V. Krivov Ingo WardinskiFrank Spahn Harald KrügerEberhard Grün 《Icarus》2002,157(2):436-455
The outer region of the jovian system between ∼50 and 300 jovian radii from the planet is found to be the host of a previously unknown dust population. We used the data from the dust detector aboard the Galileo spacecraft collected from December 1995 to April 2001 during Galileo's numerous traverses of the outer jovian system. Analyzing the ion amplitudes, calibrated masses and speeds of grains, and impact directions, we found about 100 individual events fully compatible with impacts of grains moving around Jupiter in bound orbits. These grains have moderate eccentricities and a wide range of inclinations—from prograde to retrograde ones. The radial number density profile of the micrometer-sized dust is nearly flat between about 50 and 300 jovian radii. The absolute number density level (∼10 km−3 with a factor of 2 or 3 uncertainty) surpasses by an order of magnitude that of the interplanetary background. We identify the sources of the bound grains with outer irregular satellites of Jupiter. Six outer tiny moons are orbiting the planet in prograde and fourteen in retrograde orbits. These moons are subject to continuous bombardment by interplanetary micrometeoroids. Hypervelocity impacts create ejecta, nearly all of which get injected into circumjovian space. Our analytic and numerical study of the ejecta dynamics shows that micrometer-sized particles from both satellite families, although strongly perturbed by solar tidal gravity and radiation pressure, would stay in bound orbits for hundreds of thousands of years as do a fraction of smaller grains, several tenths of a micrometer in radius, ejected from the prograde moons. Different-sized ejecta remain confined to spheroidal clouds embracing the orbits of the parent moons, with appreciable asymmetries created by the radiation pressure and solar gravity perturbations. Spatial location of the impacts, mass distribution, speeds, orbital inclinations, and number density of dust derived from the data are all consistent with the dynamical model. 相似文献
20.
针对天文观测数据不等间隔的特点,利用Jurkevich方法对黑洞候选体X射线双星Cyg X-1近16年的Rossi X-ray Timing Explorer(RXTE)All-Sky Monitor(ASM)数据进行了频谱分析,并结合Kidger周期存在可信度的判据,发现Cyg X-1存在363±11.5 d的光变周期,但没有发现420 d的光变周期,而且150 d的光变周期可能仅仅是51±1.4 d光变周期的观测表象。 相似文献