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1.
本用球对称扰动模型导出了星系暗晕的平均密度与形成时间的关系,并由此估算银河系的形成时间tv,我们把球状星团的年龄作为银河系年龄tG的代表。则tG+tV是宇宙年龄,对Ωλ=0,0.07和0.8的平坦宇宙模型,本计算并讨论了能与它相洽的哈毂常数的范围,结果表明,若哈勃常数大到80km·s^-1·Mpc^-1左右,引入宇宙常数并不一定能解决宇宙年龄的矛盾。 相似文献
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大爆炸宇宙学模型有6个基本参数-宇宙年龄t0,哈勃常数H0,宇宙物质密度参数Ω0,减速因子qo,以及与宇宙学常数A和宇宙的曲率k有关的另外两个参数Ω0A≡a3h^2,0,ΩR≡-k/H^。简要介绍了国际上对0和H0的最近研究进展。 相似文献
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大爆炸宇宙学模型有6个基本参数一宇宙年龄t0,哈勃常数H0(或哈勃参数h≡H0/100km·s-1·MPc-1),宇宙物质密度参数Ω0,减速因子q0,以及与宇宙学常数A和宇宙的曲率k有关的另外两个参数Ω0A≡A/3H,ΩR≡-K/H。简要介绍了国际上对t0和H0的最近研究进展。由于观测上和理论上都还存在着相当多的不确定因素,目前对这两个参数的取值大小仍然有很大的争议。总的说来,对于宇宙的年龄t0,较普遍的看法是t>11Gyr,其最可见值为t0≈13Ggr。对于哈勃常数H0,如果所测的天体距离尺度较小,则通常给出较大的值h≈0.6-08;而如果所测天体距离尺度较大,则通常给出较小的值h≈0.4-0.6。最近哈勃空间望远镜对M100的观测绘出h≈0.8,这一测量结果仍然含有不确定因素,因而还不能认为H0的大小已有定论。 相似文献
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在X射线观测提高了星系团质量和半径测量精度的新形势下,本文讨论了宇宙常数不等于零的平坦宇宙冷暗物质结构形成模型,利用球对称扰动区在宇宙常数不为零时的动力学方程的解,估计了星系团形成红移与宇宙常数是否为零的关系,计算了星系团质量函数随红移的演化.计算表明,红移为零时星系团的数密度基本上由谱参数Γ决定.若假定星系团质量只有20%的不确定性,可限定Γ的适用范围约为0.15-0.32.高红移星系团的数密度观测不仅有可能对宇宙常数是否为零作出鉴别,而且当精度够高时还能对宇宙物质密度的大小作出限制 相似文献
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中微子静止质量与Lemaitre模型 总被引:1,自引:0,他引:1
本文根据最近关于中微子静质量可能不为零的实验,用Lemaitre模型讨论了中微子静止质量及宇宙年龄对宇宙常数项∧和哈勃常数H_0的限制,并得出了∧的上限∧≤15×10~(-57)/cm~2和H_0的可能范围. 相似文献
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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 相似文献
12.
B. P. Kondratyev 《Solar System Research》2013,47(1):1-10
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. 相似文献
13.
M. V. Samokhin 《Earth, Moon, and Planets》1993,61(1):29-37
Using the well-known equation for the normal component of the current which exist near the tangential discontinuity in the plasma in the case of the frozen-in magnetic field, and supposing that the current closes in the ionosphere in the auroral oval in the region 1, one calculates and compares with the data of observations the dependence of the density of the field-aligned current at the level of the ionosphere on the local time. 相似文献
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Yoshio Kubo 《Celestial Mechanics and Dynamical Astronomy》2009,105(4):261-274
We calculate the so-called convective term, which shows up in the expression for the angular velocity of the elastic Earth,
within the Andoyer formalism. The term emerges due to the fact that the elasticity-caused perturbation depends not only on
the instantaneous orientation of the Earth but also on its instantaneous angular velocity. We demonstrate that this term makes
a considerable contribution into the overall angular velocity. At the same time the convective term turns out to be automatically
included into the correction to the nutation series due to the elasticity, if the series is defined by the perturbation of
the figure axis (and not of the rotational axis) in accordance with the current IAU resolution. Hence it is not necessary
to take the effect of the convective term into consideration in the perturbation of the elastic Earth as far as the nutation
is related to the motion of the figure axis. 相似文献
16.
Range of values of the Sun's mass quadrupole moment of coefficient J2 arising both from experimental and theoretical determinations enlarge across literature on two orders of magnitude, from
around 10-7 until to 10-5. The accurate knowledge of the Moon's physical librations, for which the Lunar Laser Ranging data reach an outstanding precision
level, prove to be appropriate to reduce the interval of J2 values by giving an upper bound of J2. A solar quadrupole moment as high as 1.1 10-5 given either from the upper bounds of the error bars of the observations, or from the Roche's theory, is not compatible with
the knowledge of the lunar librations accurately modeled and observed with the LLR experiment. The suitable values of J2 have to be smaller than 3.0 10-6.
As a consequence, this upper bound of 3.0 10-6 is accepted to study the impact of the Sun's quadrupole moment of mass on the dynamics of the Earth-Moon system. Such as
effect (with J2 = 5.5±1.3 × 10-6) has been already tested in 1983 by Campbell & Moffat using analytical approximate equations, and thus for the orbits of
Mercury, Venus, the Earth and Icarus. The approximate equations are no longer sufficient compared with present observational
data and exact equations are required. As if to compute the effect on the lunar librations, we have used our BJV relativistic
model of solar system integration including the spin-orbit coupled motion of the Moon. The model is solved by numerical integration.
The BJV model stems from general relativity by using the DSX formalism for purposes of celestial mechanics when it is about
to deal with a system of n extended, weakly self-gravitating, rotating and deformable bodies in mutual interactions.
The resulting effects on the orbital elements of the Earth have been computed and plotted over 160 and 1600 years. The impact
of the quadrupole moment of the Sun on the Earth's orbital motion is mainly characterized by variations of
,
, and
. As a consequence, the Sun's quadrupole moment of mass could play a sensible role over long time periods of integration of
solar system models.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Wu Lin-xiang 《Chinese Astronomy and Astrophysics》1992,16(4):427-433
By means of a simple relation between the velocity v of the fluid particle and the velocity vf of the photospheric footpoint of the magnetic field line vz and Bz being respectively the components of v and the magnetic field B normal to the photospheric surface, it is shown formally that through the phtospheric surface the transport of all the quantities attributed to the magnetic field, such as the magnetic flux, the magnetic energy and the helicity, is independent of vz, and vf is the only kinematical quantity on which the transport depends. In addition, in the neighborhood of the neutral line the velocity vl of the moving curve of constant Bz is found to be equal approximately to the component of v or vf in the direction of vl. Since vl can be measured or extimated, so can the components of v and vf near the neutral line. 相似文献
18.
L. E. Cram 《Solar physics》1976,48(1):3-19
When the K-corona is formed by the scattering of photospheric radiation from free electrons, the Fraunhofer lines are greatly broadened by the thermal motions of the hot electrons. This paper discusses the possibility of measuring the coronal electron temperature from the residual depressions in the K-coronal spectrum. If the ratio of the intensities at 4100 Å and 3900 Å can be measured to an accuracy of ±1%, the coronal temperature can be inferred to an accuracy of ±0.2 MK. The temperature of a coronal inhomogeneity may also be measured by this method, provided the position angle is known.Now at Fraunhofer Institute, Freiburg, Germany. 相似文献
19.
G. M. Petrov 《Astrophysics and Space Science》1991,177(1-2):269-270
The classical method of determination of the absolute azimuth (or Bessel's parameter n) can secure sufficiently precision for RA from observations of stars at high geographical latitudes during polar night only. 相似文献
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介绍和论述了在后牛顿引力理论(PPN形式)中在优越参考系和非优越参考系中经过参数化后引力常数变化对地球自转产生的效应,其中特别重点介绍了年周期变化的效应。此外也将理论结果同观测结果相对比。 相似文献