共查询到20条相似文献，搜索用时 93 毫秒
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简述了确定奎先达坂为我国天文台址资源考察选点的历史过程;奎选达坂的概况,最后给出了１９９５年１月１日－１２月３１日定点气象和天文可用时间的观测结果。 相似文献
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Klaus Jockers 《Solar physics》1968,3(4):603-610
The stability of the solar wind is studied in the case of spherical symmetry and constant temperature. It is shown that the stability problem must be formulated as a mixed initial and boundary-value problem in which are prescribed the perturbation values of velocity and density at an initial time and additionally the velocity perturbation at the base of the corona for all times. The solution is constructed by linear superposition of normal solutions, which contain the time only in an exponential factor. The stability problem becomes a singular eigenvalue problem for the amplitudes of the velocity and pressure perturbations, since additionally to the boundary condition at the base of the corona one must add the condition that the amplitudes behave regularly at the critical point. It is proved that only stable eigenvalues exist. 相似文献
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P. L. Hammersley F. Garzón T. J. Mahoney M. López-Corredoira M. A. P. Torres 《Monthly notices of the Royal Astronomical Society》2000,317(3):L45-L49
We present near-infrared colour–magnitude diagrams and star counts for a number of regions along the Galactic plane. It is shown that along the l =27°, b =0° line of sight there is a feature at 5.7±0.7 kpc with a density of stars at least a factor of 2 and probably more than a factor of 5 times that of the disc at the same position. This feature forms a distinct clump on an H versus J − H diagram and is seen at all longitudes from the bulge to about l =28°, but at no longitude greater than this. The distance to the feature at l =20° is about 0.5 kpc further than at l =27°, and by l =10° it has merged with, or has become, the bulge. Given that at l =27° and l =21° there is also a clustering of very young stars, the only component that can reasonably explain what is seen is a bar with half-length of around 4 kpc and a position angle of about 43°±7°. 相似文献
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A possible variation of the photospheric temperature from the equator to the poles is investigated through the observation of the variation of the equivalent width of selected spectral lines sensitive to temperature variations. The present observations, made during the summer of 1964, show that the temperature variations, if any, must roughly be smaller than 1% of the limit temperature. A possible dependence of the temperature variations on the phase of the solar cycle has also been examined and it seems that no definite statement may be done at present. There are, however, some reasonable suspects that no temperature difference between poles and equator may exist at any time. 相似文献
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The ratios of radio to optical diameter of the solar disc at 10.7 and 3 cm wavelengths are examined. The radio observations are daily east–west scans of the solar disc, made over the period 1975–1992, which includes almost two complete solar cycles. We find that the apparent disc diameter is slightly greater at solar minimum than it is at solar maximum, suggesting that the radio diameter varies over the cycle. Moreover, the ratio is smaller at 3 cm wavelength than it is at 10.7 cm, at both solar maximum and minimum. 相似文献
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The flash spectra of the partial Sun and the chromosphere were obtained at the total solar eclipse on 7 March, 1970. We studied the distributions of the surface brightness of the continuum at six wavelengths in the visual region to compare them with the previous observations and the existing model atmospheres. All of the distributions show a shallow dip and a small hump similar to those of Heintze's observation at the 1954 eclipse. But the hump in our results is of quite a different type from that given by Heintze's revised model. It was found that none of the existing model atmospheres can reproduce this hump. The intensity distribution in the low chromosphere was also examined. 相似文献
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We apply the numerical technique of Poincare surface of section to investigate the dichotomy present in the Earth-Moon system, considering the framework of planar, circular, restricted three-body problem. A study on the transition of quasi-periodic orbits (oscillatory type dichotomy) present at the Jacobi constant C=2.85 shows that the dichotomy discussed here exist not at a particular value of the mass ratio and the Jacobi constant. It is observed that as C increases, the range of mass ratio at which the dichotomy pertains increases, even though the mass ratio at which the transition of orbits takes place decreases. 相似文献
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The notion that Mercury modulates considerably the solar wind velocity at the orbit of the Earth (Nikulin, 2014) is erroneous. It is not grounded in experimental data. Quantitative estimates also suggest that this effect should be negligible at such large distances from a planet that small. The assertion that this effect may be used in practice to improve the accuracy of prediction of the solar wind velocity (Nikulin, 2014) is unfounded as well: no credible observational and theoretical evidence in favor of it has been offered. 相似文献
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The solar magnetic field maps every point in the corona to a corresponding place on the solar surface. Identifying the magnetic
connection map is difficult at low latitudes near the heliospheric current sheet, but remarkably simple in coronal hole interiors.
We present a simple analytic magnetic model (‘pseudocurrent extrapolation’) that reproduces the global structure of the corona,
with significant physical advantages over other nearly analytic models such as source-surface potential field extrapolation.
We use the model to demonstrate that local horizontal structure is preserved across altitude in the central portions of solar
coronal holes, up to at least 30 Rs, in agreement with observations. We argue that the preserved horizontal structure may be used to track the magnetic footpoint
associated with the location of a hypothetical spacecraft traveling through the solar corona, to relate in situ measurements of the young solar wind at ∼10–30 Rs to particular source regions at the solar surface. Further, we discuss the relationship between readily observable geometrical
distortions and physical parameters of interest such as the field-aligned current density. 相似文献