流星的摄影观测技巧

一、流星摄影观测的意义１９９８年１１月狮子座流星雨已经过去,但是随着坦普尔－塔特尔彗星的回归,１９９９年的１１月我们还可能看到狮子座流星雨的再现,这无疑又给天文爱好者们一线希望。许多人都想用相机记录下那一令人兴奋的场面,留作永久的纪念。然而,流星的摄...     

流星暴的航天定义

定义ZHR^*以每小时穿过1000平方公里天顶截面的，能在铝质表面打出直径不小于1厘米的弹坑的流星体数，作为流星群对航天安全威胁强度的定量标志，给出了从ZHR到ZHR^*的换算公式．用ZHR^*取代ZHR来评价20世纪90年代以来的一些强流星雨，发现1998年的贾可比尼(天龙座)流星雨对航天安全来说，是比公认的1999、2001、2002年3次狮子座流星暴强数倍的更强流星暴．     

1998～2000年狮子座流星雨的预报和观测

“1998年狮子座流星雨可能是暴雨，最佳观测地在东亚”的预报，客观上加速了中国对流星雨的现代研究。几年来，对狮子座流星雨的观测和研究，是在全国狮子座流星雨联测小组的组织和领导下发展起来的。这包括使用目视方法、照相方法和无线电方法的观测，以及组织广大天文爱好者在全国范围内的观测。我们的确也观测到了很多重要的现象，如流星雨的纤维结构、尺度分布和质量密度分布的变化等等。我们发展了数据处理方法，将处理其它天文观测数据的“时间窗”方法移植到了流星雨的数据处理中。这一方法如今在流星雨研究中已经在世界上普遍使用了。我们还提出了流星雨的质量流参量ZHMR，它对于今后流星雨的观测比较和预报可能更加有用。在雷达观测方面，我们观测到了1998年所期待的流星雨强度主峰。在此主峰过了大约18h之后，又观测到了地球电离层的反常爆发。从1998年连续两天狮子座流星雨不同的表现，以及从全国不同地区的观测得到的流星质量分布系数的差异，我们提出了大、小2种不同粒子的混合流模型，很好地解释了观测到的现象。从天体力学的基本公式出发，我们发现流星群轨道升交点和其母彗星轨道升交点之差，不仅与当时的抛射速度，而且与彗星抛出这些尘埃粒子时在轨道上的位置有关。对于1998年的观测，最可能的是这些粒子是彗星在1933年回归的时候、在距离太阳1．44A．U．距离的时候抛射出来的。按照传统的统计图分析方法，我们还对1999—2001年的狮子座流星雨强度进行了预报。事实证明，我们对1999和2000年的预报的准确性还是很高的。此外，我们还在狮子座流星雨的照相观测、轨道计算以及其它方面做了一些工作，本文仪仅是对我们所做的一些主要工作进行了一个小结。     

1998～2000年狮子座流星雨的预报和观测

"1998年狮子座流星雨可能是暴雨,最佳观测地在东亚"的预报,客观上加速了中国对流星雨的现代研究。几年来,对狮子座流星雨的观测和研究,是在全国狮子座流星雨联测小组的组织和领导下发展起来的。这包括使用目视方法、照相方法和无线电方法的观测,以及组织广大天文爱好者在全国范围内的观测。我们的确也观测到了很多重要的现象,如流星雨的纤维结构、尺度分布和质量密度分布的变化等等。我们发展了数据处理方法,将处理其它天文观测数据的"时间窗"方法移植到了流星雨的数据处理中。这一方法如今在流星雨研究中已经在世界上普遍使用了。我们还提出了流星雨的质量流参量ZHMR,它对于今后流星雨的观测比较和预报可能更加有用。在雷达观测方面,我们观测到了1998年所期待的流星雨强度主峰。在此主峰过了大约18h之后,又观测到了地球电离层的反常爆发。从1998年连续两天狮子座流星雨不同的表现,以及从全国不同地区的观测得到的流星质量分布系数的差异,我们提出了大、小2种不同粒子的混合流模型,很好地解释了观测到的现象。从天体力学的基本公式出发,我们发现流星群轨道升交点和其母彗星轨道升交点之差,不仅与当时的抛射速度,而且与彗星抛出这些尘埃粒子时在轨道上的位置有关。对于1998年的观测,最可能的是这些粒子是     

流星雨摄影观测记录的罕见现象

2001年狮子座流星雨,是几百年来难得有机会在中国观测到的一场流星暴。在我们收集到的照相观测资料中,发现了一些特殊的、还未引起广泛注意的流星现象。"蛇行"的流星以及螺旋形并带有辐条结构的流星余迹,早在我国古代记录中就可以找到印证。现代的照相技术,不仅直观地显示了文字难以描述的颜色、形态和变化,而且提供了可永久性进行测量的记录。其中包括罕见的对流星余迹的双站观测资料。用常规的"高空风作用"难以解释这些观测现象。它们可能反映了流星带电体与地球磁场的相互作用。     

1998年德令哈狮子座流星雨目视观测及初步分析

根据中国－荷兰狮子座流星雨合观测1998年11月13日至18是日在紫金山天文台德令哈观测站观测所得的数据，以及同期中国其他地方的观测数据，分析了1998年狮子座流星雨的分布特征，提出此次地球所遭遇的流星群带呈3层结构。     

2009年狮子座流星雨结果简报

在2001年前后狮王怒吼以后,有科学家预报指出,在接下来的两个33年周期里（即2033年前后和2066年前后）,狮子座流星雨将不会有大的作为,下一次大爆发很可能要等到2099年前后去了。这基本宣告了所有现在活着的人恐怕再也看不到狮子座流星雨的爆发了。虽然,目前对流星雨的预报还很不准确,尤其是对于较长时间以后的预报,但是,人们还是不由得担心起来,是不是真的在有生之年再也看不到流星暴雨了？     

我国古代记录的特殊流星现象与现代印证

中国古代有着大量的对于流星和流星雨的观测记录，最早可以追溯到3000多年以前。在这些珍贵的记录中，不仅有对于流星的一般描述，而且还有一些至今不能完全理解的特殊流星现象的记录。基于现代对电声变换流星声、流星体的螺旋线形运动、流星的颜色变化和流星的分裂等等的研究，列出在中国古代文献中可以查找到的有关记录。这些记录，不仅是世界文化宝库的一部分，而且对于今天的研究仍有实用价值。对电声变换流星声的报道，只是近20年来，才确立了的并非是观测者的臆想。流星的现代彩色照相观测，更真实地记录和展现了其他的特殊流星现象和它们的发生与演变。这些古代记录与现代的流星观测的对比，可以起到相互印证的作用。     

1999年“狮王”观测应注意的几点问题

１）９９年３有可能成为狮子座流星雨（ＬＥＯ）的最高峰年,有望突破１０００颗／小时以上的流量。因为１９９９年已进入有关历史统计的多发区,在１９９７年第五期《天文爱好者》上,徐品新先生曾介绍过ＣｏｍｅｔＴｅｍｐｅｌ－Ｔｕｔｌｅ近旁尘埃云分布的平面图,从图...     

2012年1月重要天象预告

又是一年的天象预报与您见面了,在接下来的12期里,我很荣幸能和大家一同见证2012年精彩的天象。同时,也希望有更多朋友通过天象预报开始关注天文,进行天文观测,并能从中收获更多的快乐。2012年虽然有很多值得关注的重要天象,但一月的天象剧场并没有给大家带来眼前一亮的感觉。象限仪流星雨是全年为数不多观测会受到月光干扰的大流量流星雨,而过近日点的P／2006 T1（levy）彗星预计也不会达到肉眼可见的亮度。只是金星、火星、木星和土星这几颗经典行星的观测条件还都不错,大家可以尽情发挥,拍些行星合月的天象照片。     

Extraterrestrial samples from low Earth orbits: techniques for their collection and analysis

In the context of dust samples collections in space, the COMET experiment (Collecte en Orbite de Matière ExtraTerrestre) was proposed for the first time in 1982. The idea of such an experiment was to collect grains with identified cometary parent body, instead of mixing all extraterrestrial contributions present in low Earth orbit. It was thus proposed to install collectors inside hermetic boxes, to have these boxes mounted outside a space station, orbiting the Earth and to have the capability of choosing the time and duration of the collection. Since 1985, the COMET experiment has been exposed three times to space (COMET-1, in October 1985 during the encounter of the Earth with the Draconid meteor stream; the EUROMIR-95 instrument, exposing collectors, during the crossing by the Earth of the Orionid meteor stream associated to comet P/Halley and, in November 1998, during the crossing by the Earth of the Leonid meteor stream associated to comet Temple-Tuttle, COMET-99). Specific collection techniques, and corresponding analytical procedures have been developed. The collected particles are the only ones accessible in the laboratory with a known cometary origin, before the return to Earth (2006) of the Stardust mission, which will collect cometary grains in the tails of comet Wild 2. Such a challenge justifies the tremendous efforts brought into play, and that are summarized here.     

近20年来狮子座流星雨预报进展

对近20年来狮子座流星雨的预报工作，进行了系统的阐述和分析。1998年Tempel-Tuttle彗星的回归，再度带来了狮子座流星雨的观测热，也大大促进了对狮子座流星雨预报工作的研究与验证。有的研究在时间预报准确度方面已显示出其模型的优越性，有的在流星雨的强度方面显示出一定的准确度。指出了两大类不同的方法实际上是在三维空间强调了不同的方面。将不同方法的优势结合起来，可能会使流星雨的预报更加成熟。     

Comet Tempel-Tuttle and the Leonid meteors

The distribution of dust surrounding periodic comet Tempel-Tuttle has been mapped by analyzing the associated Leonid meteor shower data over the 902–1969 interval. The majority of dust ejected from the parent comet evolves to a position lagging the comet and outside the comet's orbit. The outgassing and dust ejection required to explain the parent comet's deviation from pure gravitational motion would preferentially place dust in a position leading the comet and inside the comet's orbit. Hence it appears that radiation pressure and planetary perturbations, rather than ejection processes, control the dynamic evolution of the Leonid particles. Significant Leonid meteor showers are possible roughly 2500 days before or after the parent comet reaches perihelion but only if the comet passes closer than 0.025 AU inside or 0.010 AU outside the Earth's orbit. Although the conditions in 1998–1999 are optimum for a significant Leonid meteor shower, the event is not certain because the dust particle distribution near the comet is far from uniform. As a by-product of this study, the orbit of comet Tempel-Tuttle has been redetermined for the 1366–1966 observed interval.     

The Leonid meteor storms of 1833 and 1966

The greatest Leonid meteor storms since the late eighteenth century are generally regarded as being those of 1833 and 1966. They were evidently due to dense meteoroid concentrations within the Leonid stream. At those times, the orbit of Comet 55P/Tempel–Tuttle was significantly nearer that of the Earth than at most perihelion returns, but still some tens of Earth radii away. Significantly reducing this miss distance can be critical for producing a storm. Evaluation of differential gravitational perturbations, comparing meteoroids with the comet, shows that, in 1833 and 1966 respectively, the Earth passed through meteoroid trails generated at the 1800 and 1899 returns.     

Observations of the 2001 Leonid meteor shower using VHF meteor radar

Every year the Earth crosses or passes near one of the dust trails left by Comet 55P/Tempel-Tuttle in its pass through the Solar System every 33.2 years. This produces a meteor shower Commonly called the Leonid. The 2001 Leonid meteor shower is one of the strongest in recent years. We present observations made by the 50 MHz all-sky meteor radar located at the Platteville Atmospheric Observatory in Colorado (40° N, 105° W). The spatial and temporal distributions of the meteor activity detected by the radar during the 2001 Leonid shower differs from the observed sporadic activity detected by VHF radars. Estimation of the radiant flux of the meteor shower of the shower by a well-known methodology is presented, and the intensity of the phenomena is discussed.     

The Dynamics of Meteoroid streams

Meteors are streaks of light seen in the upper atmosphere when particles from the inter-planetary dust complex collide with the Earth. Meteor showers originate from the impact of a coherent stream of such dust particles, generally assumed to have been recently ejected from a parent comet. The parent comets of these dust particles, or meteoroids, fortunately, for us tend not to collide with the Earth. Hence there has been orbital changes from one to the other so as to cause a relative movement of the nodes of the meteor orbits and that of the comet, implying changes in the energy and/or angular momentum. In this review, we will discuss these changes and their causes and through this place limits on the ejection process. Other forces also come into play in the longer term, for example perturbations from the planets, and the effects of radiation pressure and Poynting–Robertson drag. The effect of these will also be discussed with a view to understanding both the observed evolution in some meteor streams. Finally we will consider the final fate of meteor streams as contributors to the interplanetary dust complex.     

Matching cometary ejection processes to the Leonids 1998–2001 using a hybrid numerical model

A new scheme for simulating meteor showers is introduced, based on a hybridization of current numerical modelling techniques. It involves an iterative method that generates particles which hit a real-scale Earth, removing the spatial and temporal blurring common to other modelling techniques. The scheme is applied to the activity profile of the Leonids 2001 using three different models of meteoroid ejection velocity and then applied to the Leonids 1998–2000 using the most favourable models. It is shown that to reproduce the observed meteor activity profiles there must be a strong concentration of ejection around perihelion. The modelling also implies that meteoroid density must be towards the higher end of the currently acceptable range, although the derived limits are not independent of the ejection velocity model. We also find that the extreme narrowness of Leonid activity peaks is not easily reproduced with outgassing over the entire day side of the comet but it is fitted well by outgassing in a restricted direction as one would expect from an outgassing jet. In addition, we show that double-peaked features, corresponding to a semihollow meteoroid streamlet, can arise in a meteor shower activity profile from outgassing during a single perihelion passage of the parent comet. It is suggested that this process caused the double-peaked feature in the first maxima of the 2001 Leonids.     

Meteor Outburst Profiles and Cometary Ejection Models

The spatial structure of meteor streams, and the activity profiles of their corresponding meteor showers, depend firstly on the distribution of meteoroid orbits soon after ejection from the parent comet nucleus, and secondly on the subsequent dynamical evolution. The latter increases in importance as more time elapses. For younger structures within streams, notably the dust trails that cause sharp meteor outbursts, it is the cometary ejection model (meteoroid production rate as a function of time through the several months of the comet’s perihelion return, and velocity distribution of the meteoroids released) that primarily determines the shape and width of the trail structure. This paper describes how a trail cross section can be calculated once an ejection model has been assumed. Such calculations, if made for a range of ejection model parameters and compared with observed parameters of storms and outbursts, can be used to constrain quantitatively the process of meteoroid ejection from the nucleus, including the mass distribution of ejected meteoroids.     

Is 2329 Orthos a dead comet?

Probably most meteor showers have a cometary origin. Investigation of Near-Earth asteroids' orbital evolution to determine whether they have related meteor showers is necessary to determine which asteroids evolved from comets. The results of calculations show that asteroid Orthos' orbit is an octuple Earth-crosser. Therefore, if Orthos has an old meteoroid stream it may produce eight meteor showers observable on the Earth. The existence of four Orthos' Northern meteor showers is confirmed by our search in the published catalogues of meteor radiants and orbits or in the archives of the IAU Meteor Data Center (Lund, Sweden).     

Orthos' meteor showers

Probably the majority of meteor showers has a cometary origin. Investigation of Near-Earth asteroids' orbital evolution to determine whether they have related meteor showers are necessary to determine which asteroids evolved from comets. The results of calculations show that asteroid Orthos' orbit is an octuple Earth-crosser. Therefore, if Orthos has an old meteoroid stream it may produce eight meteor showers observable on the Earth. The existence of four Orthos' Northern meteor showers is confirmed by our search in the published catalogues of meteor radiants and orbits or in the archives of the IAU Meteor Data Center (Lund, Sweden).