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一年之内三大天象奇观──百武彗星、海尔-波普彗星和日全食李启斌,赵刚从今年3月到明年3月的一年之内,百武彗星、海尔-波普彗星、日全食三大天象奇观相继出现,这一千载难逢的机遇,受到了公众的广泛关注。这里我们向大家介绍一下这些天象的基本情况。一、海尔-波... 相似文献
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从去年年底至今年年初,似乎什么彗星也比不上Lovejoy彗星那么出彩。它真正成为了一颗明星,闯进了太阳的禁宫,又勇猛地一路冲杀出来,并以灿烂的光辉显示它几十年才有一个的英雄形象。掠日彗星家族中像它这样幸运的,当然非常少。现在几乎每一天,SOHO彗星都可以观测到有一颗掠日彗星被太阳火葬。去年夏天,一颗比Lovejoy彗星小得多的彗星,被太阳神严厉地处以了极刑。不过,天文学家有幸第一次目睹了整个的惩罚过程。 相似文献
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Comet C/1999 S4 (LINEAR) was exceptional in many respects. Its nucleus underwent multiple fragmentations culminating in the complete disruption around July 20, 2000. We present circular polarization measurements along the cuts through the coma and nucleus of the comet during three separate observing runs, in June 28-July 2, July 8-9, and July 21-22, 2000. The circular polarization was detected at a rather high level, up to 0.8%. The left-handed as well as right-handed polarization was observed over the coma with the left circularly polarized light systematically observed in the sunward part of the coma. During our observations the phase angle of the comet varied from 61 up to 122°, which allowed us to reveal variations of circular polarization with the phase angle. Correlation between the degree of circular polarization, visual magnitude, water production rate, and linear polarization of Comet C/1999 S4 (LINEAR) during its final fragmentation in July 2000 was found. The mechanisms that may produce circular polarization in comets and specifically in Comet C/1999 S4 (LINEAR) are discussed and some tentative interpretation is presented. 相似文献
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Comet NEAT C/2001 Q4 was observed for linear polarization using the optical polarimeter mounted at the 1.2 m telescope at Mt. Abu Observatory, during the months of May and June 2004. Observations were conducted through the International Halley Watch narrow band (continuum) and BVR broad band filters. During the observing run the phase angle ranged from 85.6° in May to 55° in June. As expected, polarization increases with wavelength in this phase angle range. Polarization colour in the narrow bands changes at different epochs, perhaps related to cometary activity or molecular emission contamination. The polarization was also measured in the cometary coma at different locations along a line, in the direction of the tail. As expected, we notice minor decrease in the polarization as photocenter (nucleus) is traversed while brightness decreases sharply away from it. Based on these polarization observations we infer that the Comet NEAT C/2001 Q4 has high polarization and a typical grain composition—mixture of silicates and organics. 相似文献
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The target of the Deep Impact space mission (NASA), Comet 9P/Tempel 1, was observed from two nights before impact to eight nights after impact using the FORS spectrographs at the ESO VLT UT1 and UT2 telescopes. Low resolution optical long-slit spectra were obtained to study the evolution of the gas coma around the Deep Impact event. Following first results of this observing campaign on the CN and dust activity [Rauer, H., Weiler, M., Sterken, C., Jehin, E., Knollenberg, J., Hainaut, O., 2006. Astron. Astrophys. 459, 257-263], this work presents a study of the complete dataset on CN, C2, C3, and NH2 activity of Comet 9P/Tempel 1. An extended impact gas cloud was observed moving radially outwards. No compositional differences between this impact cloud and the undisturbed coma were found as far as the observed radicals are concerned. The gas production rates before and well after impact indicate no change in the cometary activity on an intermediate time scale. Over the observing period, the activity of Comet 9P/Tempel 1 was found to be related to the rotation of the cometary nucleus. The rotational lightcurve for different gaseous species provides indications for compositional differences among different parts of the nucleus surface. 相似文献
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Here we estimate the regions of stability, fragmentation, and destruction for cometary bodies versus rotational breakup in the radius-rotational period plane. By testing different plausible physical models of the cometary nucleus equation of state, we show that the plane is divided into 3 segments: the allowed, damaged, and forbidden regions. We then compare the location of well-observed comets with respect to the separation lines. The range of constituent material parameters from the literature for cometary nuclei are used to show that all the observed comets lie in the allowed region, except for Comet C/1995 O1 (Hale-Bopp), which resides in the damaged region (where the body is fractured and only held together gravitationally). We speculate that the extremely high activity demonstrated by Comet Hale-Bopp during the 1997 apparition may have been due to its highly fractured state. Comet Hyakutake, observed to emit fragments at perigee in 1996, may be near the boundary of the damaged region. Comet C/1999 S4 (LINEAR) was solidly in the rotationally allowed region, making its disintegration in July 2000 due to centrifugal forces unlikely. In contrast to the comets, the centaurs do not cluster in the allowed region, with the majority falling instead into the rotationally damaged and forbidden regions. The centaurs are only stable against breakup assuming much stronger solid water ice properties, strongly suggesting that on the whole, these bodies have different bulk physical properties than cometary nuclei. 相似文献
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Ichiro Hasegawa Syuichi Nakano 《Monthly notices of the Royal Astronomical Society》2003,345(3):883-888
The orbit of Comet C/2002C1 (Ikeya–Zhang) has a similarity to that of Comet C/1661C1 (Hevelius), and the numerical integration of the motion of C/2002C1 backward shows a possible linkage of those two comets. Thus, 153P/Ikeya–Zhang was designated a periodic comet. Historical records of comets in 877 and 1273 are also identified with Comet 153P/Ikeya–Zhang. The integrated orbital elements during 77 and 2362, and historical records of the comet are also presented and discussed. 相似文献
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Our polarimetric database contains six comets, C/1975 V1 (West), 16P/Brooks 2,C/1988 A1 (Liller), D/1996 Q1 (Tabur), C/1999
S4 (LINEAR), and C/2001 A2(LINEAR), which can be related to the group of split comets. Comets West, S4(LINEAR) and A2 (LINEAR)
were observed during splitting. We compare thepolarimetric measurements of the dust particles in these comets, sometimes togetherwith
available photometric and colorimetric data, with those in normal comets. Weconclude that there is no significant evidence
for differences of polarization betweentidally split comets (e.g., Brooks 2), dissipating comets (e.g., Tabur), non-tidally
splitcomets (e.g., West) and normal comets. The total disintegration of Comet S4 (LINEAR), however, did produce significant
changes in the observed properties of dust. 相似文献
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R.L. Branham 《Astronomische Nachrichten》2009,330(4):346-350
Orbits are calculated for Comet C/1845 L1 (the Great June Comet) and C/1846 D1 (de Vico), the former based on 157 observations in right ascension and 152 in declination and the latter on 10 and 9, respectively. Both orbits are hyperbolic and statistically distinguishable from parabolas. Statistical tests indicate that the residuals are random and thus the orbits satisfactory. The Great June Comet is in no way associated with the comet Tycho Brahe observed in 1596 (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
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William Liller 《Planetary and Space Science》1997,45(12):1505-1513
Systematic CCD photometry of Comet 1995 O1 (Hale-Bopp) began in early August 1995 shortly after its discovery (IAU Circular 6187) and continued until mid-November 1996. The light curve derived from a 34″ square centered on the nucleus shows clearly and objectively how the inner regions of the comet brightened during this 15 month period. Possible connections between sudden brightenings and reported outbursts are investigated. During the interval August–December 1995, the magnitude of the comet showed strong evidence of a periodicity of 20±5 days with a full amplitude of approximately 0.20 mag. It is noteworthy that this result spans both the period of 18 days suggested by Sekanina (1995, 1996) and the “superperiod” of 22±2 days reported by Jorda et al. (1997). However, in 1996 neither this periodicity nor any other could be detected with certainty in the photometric data. 相似文献
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IWAN P. WILLIAMS G. O. RYABOVA A. P. BATURIN A. M. CHERNITSOV 《Earth, Moon, and Planets》2004,95(1-4):11-18
The orbit of asteroid 2003 EH1 is very similar to the mean orbit of the Quadrantid meteoroid stream so that a close relationship
between the two is very likely. It has already been suggested that Comet C/1490 Y1 could be the parent of the Quadrantids.
If this is the case, then some relationship between the comet and the asteroid might be expected. The orbit of C/1490 Y1 is
based on a short observing arc of about 6 weeks and all the observations were with the naked eye, so that its elements are
very poorly determined. Hence, forward integration to determine whether asteroid 2003 EH1 represents the re-discovery of the
dormant nucleus of C/1490 Y1 is not feasible. Instead we choose to integrate back in time the orbit of 2003 EH1, which is
far better determined, and a family of 3500 clones, all of which are moving on an orbit that is consistent with the present
known orbit of 2003EH1. We compare the results primarily with the recorded observations of the comet rather than the orbit
of the comet derived by Hasegawa. We find that one clone is consistent with these observations. 相似文献
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Comet 1996 B2 (Hyakutake) displayed strong evidence for break-up, with a prominent antisunward dust spike and fragments traveling antisunward for many days after an eruptive event in late March 1996. Because of its high orbital inclination and rapid southward motion after perihelion, its post-perihelion activity was not well monitored from the ground. The SWAN all-sky Lyman-alpha camera on the SOHO spacecraft was ideally placed for long-term monitoring of the hydrogen coma of Comet Hyakutake both before and after perihelion. The SWAN images were analyzed with a new time-resolved model (TRM) that provides daily averages of the water production rate and an estimate of the hydrogen atom lifetime (dominated by charge exchange with solar wind protons) during extended periods throughout the apparition. A long-term variation of water production rate of , where r is the heliocentric distance in AU was found. The daily average values of the production rate covered the March 19 outburst and two more outbursts seen in the April before perihelion, which had progressively shorter durations at respectively smaller heliocentric distances. The long-term variation of the production rate was found to be consistent with the seasonal effect predicted by the jet rotation model of Schleicher and Woodney [2003. Analyses of dust coma morphology of Comet Hyakutake (1996 B2) near perigee: Outburst behavior, jet motion, source region locations, and the nucleus pole orientation. Icarus 162, 190-213] when added to a more steady source that is about two-thirds of the maximum of the jet source. The seasonal effect in their model found the dust jet source largely not illuminated after perihelion, coinciding with somewhat reduced overall activity and the absence of outbursts and fragmentation. The locations of the dust jets appear to be responsible for the outbursts and fragmentation before perihelion. The erratic behavior of the pre-perihelion jet sources as contrasted with the smoother variation from the rest of the surface after perihelion indicates there is a strong heterogeneity in the physical make-up of active areas on the nucleus. 相似文献