天象观测

天象观测一九九七年三月天象月初，太阳的视赤纬为一７°３９′．１；月末，太阳的视赤纬为＋４°０５′．１，本月太阳由宝瓶座运行至双鱼座。今年３月９日将发生日全食，全食带于９日晨８时４４分（北京时间）从俄罗斯比斯克以南和我国新疆阿勒泰以北地区开始，经蒙古、...     

天象观测

天象观测一九九八年五月天象月初,太阳的视赤纬为＋１４°５６′．９;月末,太阳的视赤纬为＋２１°５１′１。太阳由白羊座运行至金牛座。６日１时０３分立夏,太阳的黄经为４５°。２１日４时０５分小满,太阳的黄经为６０°。月亮过远地点、近地点的时间分别为８日...     

天象观测

天象观测一九九八年一月天象月初，太阳的视赤纬为－２３°０６′．５；月末，太阳的视赤纬为－１７°２９′．８。本月太阳由人马座运行至摩羯座。５日２１时１８分小寒，太阳的黄经为２８５°。２０日１４时４６分大寒，太阳的黄经为３００°。月亮过近地点、远地点的时...     

天象观测

天象观测一九九六年一月天象月初，太阳的视赤纬为－２３°０８′．６；月末，太阳的视赤纬为－１７°３８′．１。本月太阳由人马座运行到摩精座。６日９时３２分小寒，太阳的黄经为２８５°。２１日２时５３分大寒，太阳的黄经为３００°。月亮过远地点、近地点的时间分...     

天象观测

天象观测一九九七年一月天象月初，太阳的视赤纬为－２３°０５’．４；月末，太阳的视赤纬为－１７°２５’．６。本月太阳由人马座运行至摩揭座。５日１５时２５分小寒，太阳的黄经为２８５°。２２日８时４３分大寒，太阳的黄经为３００°。月亮过近地点、远地点的时间...     

天象观测

天象观测一九九八年九月天象月初,太阳的视赤纬为＋８°２５′．９;月末,太阳的视赤纬为－２°３８′０。本月太阳由狮子座运行至室女座。８日４时１６分白露,太阳的黄经为１６５°。２３日１３时３７分秋分,太阳的黄经为１８０°。月亮过近地点、远地点的时间分别...     

射电源0716 714和0839 187的光学定位

利用北京天文台具有ＣＣＤ终端的６０ｃｍ光学望远镜（Ｖ波段）观测射电源的光学对应体，得到了０７１６＋７１４和０８３９＋１８７精确的光学位置。参考星表采用拉帕尔玛（ＬａＰａｌｍａ）的１８ｃｍ全自动子午环观测资料编制的ＣＡＭＣ星表，该星表是ＦＫ５星表系统。两颗源位置的内符精度约为０．″１９，与其他作者给出的光学和射电位置观测结果分别进行了比较     

天象观测

天象观测一九九七年五月天象月初，太阳的视赤纬为＋１５＇０１＇．３；月末，太阳的视赤纬为＋２１“５３’．２。本月太阳由白羊座运行至金牛座。５日１９时１９分立夏，太阳的黄经为４５”。２１日８时１８分小满，太阳的黄经为６０”。月亮过近地点、远地点的时间分别...     

陕台光电等高仪(Ⅰ型)初始星表(摘要)

1978年初至1981年初,我们用陕台光电等高仪(Ⅰ型)进行了专门的星表观测。获得的星表包括777颗两次过等高圈的恒星的赤径改正△α和赤纬改正△δ。其中有FK4星357颗,FK4supp星189颗,GC星231颗。对于|cosq|≤0.3的星没有计算△δ。所有FK4星△α、△δ的平均精度分别为±0.0036和±0″.063。另外,还给出了43颗一次过等高圈的恒星的赤经改正△α和2颗星的赤纬改正△δ。为有效地扩充待测星数,除在时间、纬度观测纲要即基本组(2小时一组)内插入适当数目的待测星外,我们增加了星表组(1小时一组)。观测方案是:星表组——基本组——星表组——星表组——基本组——星表组或者星表组——基本组——基本组——星表组。星表的系统完全由基本组的FK4星决定。将各基本组化到平均系统以后,所有的星表组及基本组内的插入星直接相对于这个平均系统求其残差平均值。     

天象观测

天象观测一九九六年九月天象月初，太阳的视赤纬为８°１５’．４；月末，太阳的视赤纬为－２°４９”．２。本月太阳由狮子座运行至室女座。７日１６时４３分白露，太阳的黄经为１６５°。２３日２时０分秋分，太阳的黄经为１８０°。月亮过远地点、近地点的时间分别为９...     

Radiative association of C and P, and Si and P atoms

The rate coefficients for the formation of carbon monophosphide (CP) and silicon monophosphide (SiP) by radiative association are estimated for temperatures ranging from 300 to 14 100 K. In this temperature range, the radiative association rate coefficients are found to vary from  1.14 × 10⁻¹⁸  to  1.62 × 10⁻¹⁸ cm³ s⁻¹  and from  3.73 × 10⁻²⁰  to  7.03 × 10⁻²⁰ cm³ s⁻¹  for CP and SiP, respectively. In both cases, rate coefficients increase slowly with the increase in temperature.     

Gravity and Topography of Moon and Planets

Planetology serves the understanding on the one hand of the solar system and on the other hand, for investigating similarities and differences, of our own planet. While observational evidence about the outer planets is very limited, substantial datasets exist for the terrestrial planets. Radar and optical images and detailed models of gravity and topography give an impressive insight into the history, composition and dynamics of moon and planets. However, there exists still significant lack of data. It is therefore recommended to equip all future satellite missions to the moon and to planets with full tensor gravity gradiometers and radar altimeters.     

Uranus and Neptune: Shape and rotation

Both Uranus and Neptune are thought to have strong zonal winds with velocities of several 100 m s⁻¹. These wind velocities, however, assume solid-body rotation periods based on Voyager 2 measurements of periodic variations in the planets’ radio signals and of fits to the planets’ magnetic fields; 17.24 h and 16.11 h for Uranus and Neptune, respectively. The realization that the radio period of Saturn does not represent the planet’s deep interior rotation and the complexity of the magnetic fields of Uranus and Neptune raise the possibility that the Voyager 2 radio and magnetic periods might not represent the deep interior rotation periods of the ice giants. Moreover, if there is deep differential rotation within Uranus and Neptune no single solid-body rotation period could characterize the bulk rotation of the planets. We use wind and shape data to investigate the rotation of Uranus and Neptune. The shapes (flattening) of the ice giants are not measured, but only inferred from atmospheric wind speeds and radio occultation measurements at a single latitude. The inferred oblateness values of Uranus and Neptune do not correspond to bodies rotating with the Voyager rotation periods. Minimization of wind velocities or dynamic heights of the 1 bar isosurfaces, constrained by the single occultation radii and gravitational coefficients of the planets, leads to solid-body rotation periods of ∼16.58 h for Uranus and ∼17.46 h for Neptune. Uranus might be rotating faster and Neptune slower than Voyager rotation speeds. We derive shapes for the planets based on these rotation rates. Wind velocities with respect to these rotation periods are essentially identical on Uranus and Neptune and wind speeds are slower than previously thought. Alternatively, if we interpret wind measurements in terms of differential rotation on cylinders there are essentially no residual atmospheric winds.     

Galactic and Stellar Dynamics: Limits and Perspectives

An elementary review about stellar and galactic dynamics is presented. Despite involving extremely classical Newtonian physics, stellar dynamics presents some fundamental difficulties rarely discussed in the literature, such as why the phase space distribution is assumed to be a smooth function of coordinates. Many systems are found to be unstable over intermediate time-scales, as more instabilities have been discovered over the years, so the old aim of describing equilibrium stable systems shifts presently toward understanding evolutive systems. From the linearized variational Boltzmann equation a distinction can be made between instabilities triggered by the chaotic part of phase space, and instabilities caused by steep gradients in the velocity part of the distribution function. The new challenges to include evolutive systems can presently only be studied efficiently with computer techniques. Future studies are likely to involve orders of magnitude more advanced computers in which parallelism will play a major role. This revised version was published online in July 2006 with corrections to the Cover Date.     

Osculating and Superosculating Intermediate Orbits and their Applications

A method of construction of intermediate orbits for approximating the real motion of celestial bodies in the initial part of trajectory is proposed. The method is based on introducing a fictitious attracting centre with a time-variable gravitational parameter. The variation of thisparameter is assumed to obey the Eddington–Jeans mass-variationlaw. New classes of orbits having first-, second-, and third-order tangency to the perturbed trajectory at the initial instant of time are constructed. For planar motion, the tangency increases by one or two orders. The constructed intermediate orbits approximate the perturbed motion better than the osculating Keplerian orbit and analogous orbits of otherauthors. The applications of the orbits constructed in Encke's methodfor special perturbations and in the procedure for predicting themotion in which the perturbed trajectory is represented by a sequenceof short arcs of the intermediate orbits are suggested.The use of the constructed orbits is especially advantageous in the investigation of motion under the action of large perturbations.     

Emerging and Decaying Magnetic Flux and Subsurface Flows

We study the temporal variation of subsurface flows of 788 active regions and 978 quiet regions. The vertical-velocity component used in this study is derived from the divergence of the measured horizontal flows using mass conservation. The horizontal flows cover a range of depths from the surface to about 16 Mm and are determined by analyzing about five years of GONG high-resolution Doppler data with ring-diagram analysis. We determine the change in unsigned magnetic flux during the disk passage of each active region using MDI magnetograms binned to the ring-diagram grid. We then sort the data by their flux change from decaying to emerging flux and divide the data into five subsets of equal size. The average vertical flows of the emerging-flux subset are systematically shifted toward upflows compared to the grand average values of the complete data set, whereas the average flows of the decaying-flux subset show comparably more pronounced downflows especially near 8 Mm. For flux emergence, upflows become stronger with time with increasing flux at depths greater than about 10 Mm. At layers shallower than about 4 Mm, the flows might start to change from downflows to upflows, when flux emerges, and then back to downflows after the active regions are established. The flows in the layers between these two depth ranges show no response to the emerging flux. In the case of decaying flux, the flows change from strong upflows to downflows at depths greater than about 10 Mm, whereas the flows do not change systematically at other depths. A cross-correlation analysis shows that the flows in the near-surface and the deeper layers might change about one day before flux emerges. The flows associated with the quiet regions fluctuate with time but do not show any systematic variation.     

Meteoritical and dynamical constraints on the growth mechanisms and formation times of asteroids and Jupiter

Thermal models and radiometric ages for meteorites show that the peak temperatures inside their parent bodies were closely linked to their accretion times. Most iron meteorites come from bodies that accreted <0.5 Myr after CAIs formed and were melted by ²⁶Al and ⁶⁰Fe, probably inside 2 AU. Rare carbon-rich differentiated meteorites like ureilites probably also come from bodies that formed <1 Myr after CAIs, but in the outer part of the asteroid belt. Chondrite groups accreted intermittently from diverse batches of chondrules and other materials over a 4 Myr period starting 1 Myr after CAI formation when planetary embryos may already have formed at ∼1 AU. Meteorite evidence precludes accretion of late-forming chondrites on the surface of early-formed bodies; instead chondritic and non-chondritic meteorites probably formed in separate planetesimals. Maximum metamorphic temperatures in chondrite groups are correlated with mean chondrule age, as expected if ²⁶Al and ⁶⁰Fe were the predominant heat sources. Because late-forming bodies could not accrete close to large, early-formed bodies, planetesimal formation may have spread across the nebula from regions where the differentiated bodies formed. Dynamical models suggest that the asteroids could not have accreted in the main belt if Jupiter formed before the asteroids. Therefore Jupiter probably reached its current mass >3-5 Myr after CAIs formed. This precludes formation of Jupiter via a gravitational instability <1 Myr after the solar nebula formed, and strongly favors core accretion. Jupiter probably formed too late to make chondrules by generating shocks directly, or indirectly by scattering Ceres-sized bodies across the belt. Nevertheless, shocks formed by gravitational instabilities or Ceres-sized bodies scattered by planetary embryos may have produced some chondrules. The minimum lifetime for the solar nebula of 3-5 Myr inferred from the total spread of CAI and chondrule ages may exceed the median lifetime of 3 Myr for protoplanetary disks, but is well within the 1-10 Myr observed range. Shorter formation times for extrasolar planets may help to explain their unusual orbits compared to those of solar giant planets.     

Opposition polarimetry and photometry of S- and E-type asteroids

The first results of the observational program devoted to simultaneous investigation of asteroid polarimetric and photometric opposition phenomena are presented. UBVRI polarimetric and V-band photometric observations of the S-type Asteroid 20 Massalia and the E-type Asteroids 214 Aschera and 620 Drakonia were carried out in 1996-1999 down to phase angles of 0.08°, 0.7°, and 1.2°, correspondingly. The S-type Asteroid 20 Massalia is characterized by the pronounced brightness opposition surge with an amplitude larger than that observed for the E-type asteroids. A sharp peak of negative polarization at small phase angles was not observed for this asteroid. The value of polarization degree at phase angle α<1° is less than 0.5% for both S and E types. The negative polarization branches of S and especially E-asteroids have an asymmetrical shape. The phase angle at which the polarization minimum occurs is close to the angle at which non-linear increase begins in the asteroid magnitude phase curves. A relation of the observed effects to the mechanism of coherent backscattering is discussed.