Halley's Comet Research Articles

The phase curve of cometary dust: Observations of comet 96P/Machholz 1 at large phase angle with the SOHO LASCO C3 coronagraph

We have analyzed brightness and polarization data of comet 96P/Machholz, obtained with the SOHO-LASCO C3 coronagraph at phase angles up to 167° and 157°, respectively. The polarization data are characteristic of a typical dusty comet. Within error limits the corresponding trigonometric fit describes the new data measured at larger phase angles as well as those of the previously known range. In the phase angle range from 110° to 167° the brightness increases almost linearly by about two orders of magnitude. The gradient is independent of wavelength. From the absence of a diffraction spike we conclude that the grains contributing significantly to the scattered light must have a size parameter $x = 2\pi r/\lambda \ge 20$, i.e. have a radius larger than 1 μ m. Fits of the data with Mie calculations of particles having a power law distribution of power index ≈ 2.5 provide a best fit refractive index $\emph{m}$ = 1.2 + $\emph{i}$0.004. In the framework of effective medium theory and on the assumption of a particle porosity $P= 0.5$ this leads to a complex refractive index of the porous medium $\emph{m}$ = 1.43 + $\emph{i}$0.009. A higher refractive index is possible for more porous grains with very low absorption. The large particle sizes are in qualitative agreement with findings derived from the analysis of the motion of cometary dust under solar radiation pressure (Fulle and coworkers, see [CITE]; [CITE] 1997) and with the in-situ measurements of the dust of Halley's comet.

Halley's comet of 87 BC on the coins of Armenian king Tigranes?

Coins of Armenian king Tigranes II the Great (95-55 BC), silver and copper-bronze tetradrachms and drachms, clearly reveal a star with a tail on the royal tiara which may be associated with the Halley's comet passage of 87 BC. If so, one has another case when astronomical events can be useful for historical chronological problems, this would be a far earlier record of Halley in Armenia than was previously known from chronicles and also one of the earliest known images of Halley's comet.

Tentative identification of pyrene as a polycyclic aromatic molecule in UV spectra of comet P/Halley: An emission from 368 to [formula omitted

Emission spectra of comet P/Halley in the 275– 710 nm wavelength range were obtained using a spectrometer mounted on the Vega 2 spacecraft, which encountered the comet on March 9, 1986. The spectra, after the removal of the dust-scattered solar continuum, show the presence of a broad-band emissive feature between 340 and 390 nm with three peaks at 371, 376 and 382 nm . Near the nucleus, the intensity increase illustrates that the molecules responsible for the emission are most likely of the parent type. Our cometary spectra were compared with UV laboratory spectra of polycyclic aromatic hydrocarbons having 4 benzenoid rings. A laser-induced fluorescence experiment conducted in the laboratory recorded the dispersed emission spectrum of pyrene under jet-cooled conditions. Moreels et al. (Astron. Astrophys. 284 (1994) 643) demonstrated that phenanthrene was a possible candidate for the four bands at 347, 356, 364 and 374 nm . The comparison between the cometary and laboratory spectra suggests the possible presence of another PAH, probably pyrene, in Halley's comet. This new suggestion illustrates the link between cometary and interstellar matter. These observations are coherent with the detection of the cometary IR band at 3.28 μm assigned to an X–CH organic compound.

The Strange and Twisted World of Pulsars

### Contents #### News The Pulsar Menagerie Pulsars Surf the Cosmic Waves Crushed by Magnetism #### Reviews [The Physics of Neutron Stars][1] J. M. Lattimer and M. Prakash [Observational Properties of Pulsars][2] R. N. Manchester Pulsars in Binary Systems: Probing Binary Stellar Evolution and General Relativity I. H. Stairs See related [Editorial][3] I n 1054 C.E., people around the world witnessed an exploding star. It burst forth on 4 July, brighter than Venus, and stayed visible in daylight for about 23 days before gradually fading from sight and memory. Chinese records called it a guest star. By the time 18th century observers rediscovered it using telescopes, all they could see was a faint smudge of light. In 1758, the French astronomer Charles Messier mistook it for Halley's comet; realizing his error, he cataloged it as M1, the first of his famous sequence of fuzzy objects that shouldn't be confused with comets. The guest star was a supernova explosion; the fuzzy object, now called the Crab Nebula (see cover), was the remnant of gas and dust it left behind. More than 200 years after Messier, astronomers heard the throbbing at the heart of the Crab and identified a pulsar—a whirling neutron star sending out steady pulses of emissions, 30 times per second—at its core. A year earlier, in 1967, Jocelyn Bell Burnell had detected similar pulsations coming from four compact sources (see Editorial on p. 489), a discovery that launched the field of pulsar research. Today astronomers have identified more than 1400 pulsars, half of them within the past 6 years. In this special section, Irion provides a concise history of pulsar research in his News story (p. 532), and Manchester reviews the demographics and properties of radio pulsars (p. 542). Getting back to basics, Lattimer and Prakash describe the interior of the neutron star (p. [536][1]). A neutron star, with an average diameter of 12 kilometers and a mass similar to the Sun's, has an interior dominated by neutrons packed as much as 10 times more densely than a typical atomic nucleus. This form of matter is so exotic that laboratories cannot recreate it; to understand it, neutron star aficionados must depend on theory and astronomical observations. The pulsations that give pulsars their name are thought to be driven by the release of energy along the magnetic poles as the field unwinds and the pulsar spin slows down. All pulsars have relatively strong magnetic fields, around 1012 gauss (compared with Earth's field of about 0.6 gauss). Recently, as Irion describes in a second News story (p. [534][4]), theory and observations have revealed the existence of magnetars, extreme pulsars with fields of 1015 gauss. Magnetars may be the source of gamma ray bursts and provide the missing link between supernovae and gamma ray bursts. Bizarre and bursty though they are, pulsars have extraordinarily regular habits. Their pulsations can be measured to within about 10 significant digits, making them more precise timers than atomic clocks. In the 1970s, however, astronomers noticed that some were slightly off—or even worse, for already befuddled theorists, speeding up. It turned out that some of these unsteady pulsars have companions—and very interesting ones, at that. Stairs reviews binary systems (p. 547), from the first extrasolar planet ever detected (which orbits a pulsar) to a two-pulsar system discovered last year. The double-pulsar system may provide the best opportunity to study relativity theory. Pulsars may hold the key to understanding gravity, and they certainly have much to tell us about the interstellar medium, odd physics such as superfluidity and strange matter, and the dynamics of binary systems. New twists are certain to emerge as researchers continue to probe their surreal reality. [1]: /lookup/doi/10.1126/science.1090720 [2]: /lookup/doi/10.1126/science.1097649 [3]: /lookup/doi/10.1126/science.304.5670.489 [4]: /lookup/doi/10.1126/science.304.5670.534

Attogram dust grains in the solar system

In this paper we conceptually develop the theory of attogram dust grain formation by the cosmic-ray ion-enhanced brittle microerosion of atmosphereless solar system bodies. According to our theory, the multicharged cosmic ray ions penetrating into the solid material of planetary satellites, asteroids, comets and smaller space bodies give rise to microscopic cylindrical overheated zones and generate mechanical impulses and thermoelastic stresses exceeding the material tensile strength. The impulses may cause micro-scale shattering of the surfaces and the ejection of ultrafine (attogram) dust particles off the parent body. The attogram grains formed by this mechanism (the so-called track-breaking mechanism) have an average mass of 10-19–10-17 g, a very flaky shape and ejection velocities of from tens to hundreds . Depending on the ejection velocity and a large array of non-gravitational forces, such grains can deposit and accumulate on the parent body surface, orbit around the body thus forming a bound dust cocoon, or finally, escape the body as ultrafine-dust wind. Quantitative data on dust contributions to these varieties of attogram population depending on the sizes and parameters of parent body material are obtained and discussed. The volumetric track-breaking resulting in attogram grain deposition in the ice-rock mixture of cometary nuclei during the whole period of their formation is analysed. Taking the example of Halley's comet we demonstrate that the mechanism under study makes it possible to quantitatively explain the in situ measured considerable excess of attogram grains within the cometary environment in its circum-solar path sections. The problem of track-breaking disintegration of small-sized bodies in the Kuiper Belt, which are permanently subjected to a cosmic-ray ion-enhanced brittle microerosion heavier than in the Main Belt, is investigated. The track-breaking survival timescale for submicron and over hundred micron-sized grains is found to be considerably smaller than the escape timescale of the Poynting-Robertson and plasma drags, as well as the collisional mechanism. Track-breaking can also be competitive to the collisional escape in the range of grain sizes of 1 to 100 microns. A quantitative analysis of the calculations shows that the present theory may adequately explain both the observable micron/submicron dust grain depletion of the Kuiper Belt and the loss of its bulk mass during evolution. Some possible observational tests for the future revealing the predicted populations of attogram dust in the solar system are also discussed.

Cometary and Interstellar Dust Analyzer for comet Wild 2

The Cometary and Interstellar Dust Analyzer (CIDA) instrument analyzes the composition of individual grains in the cometary coma. As each particle impacts a silver plate, the high‐impact energy due to the relative velocity of the spacecraft as it flies through the coma causes the elements and molecular compounds in the particle to become ionized. Using a fast time‐of‐flight mass spectrometer, a complete set of ions are detected for each impact, from a mass range of 1 (atomic hydrogen) up to a few thousand atomic mass units, encompassing all elements in the periodic table and many molecules, such as organic compounds. This experimental technique has already been applied with excellent success at Halley's comet, and the CIDA derivative instrument is flying on the Stardust mission, which will encounter comet Wild 2 in January of 2004. The data returned will give clues to the elemental and chemical composition of the dust component of this comet.

Farthest, Faintest detection of a comet

Astronomers searching for small Trans‐Neptunian Objects announced on 1 September that they have captured the most distant observation ever made of a comet, and also the faintest comet observation.The object happens to be Halley's Comet, which scientists at the European Southern Observatory's Very Large Telescope in Paranal, Chile, have detected at a heliocentric distance of 28.06 AU.

Meteors and showers a millennium ago

Meteors can be classified into either sporadic meteors or showery meteors. We compile the meteor records in the astronomical archives in the Chronicle of the Koryo dynasty (918-1392), and investigate the spatial distribution of meteor streams along the orbit of the Earth from the 10th century to the 14th century. We see that meteors from meteor streams signalize themselves over noisy sporadic meteors, and that the seasonal activity of sporadic meteors was apparently regular. We discover the presence of a few meteor streams by analysing about 700 meteors in the Koryo period. We also compile the records of meteor showers and storms in the chronicles of Korea, Japan, China, Arab, and Europe, and compare their appearance dates with those of showers obtained above, as well as with the modern observations. We confirm that the three sets of data are in agreement with each other. The representative meteor showers are the Perseids, the Leonids, and the $\eta$-Aquarids/Orionids pair formed by Halley's comet. The other weak or relic meteor streams are also observable but uncertain. Hence, we witness the regularity of meteor activity, which is seen to persist for a millennium.

Basic scientific results from the investigation of the halley comet coma glow by data of the three-channel spectrometer on board the venus-halley interplanetary station

More than 3000 unique spectra of the Halley comet in the near UV and visible region on 9, 10, and 11 March 1986 are registered and processed. Two-dimensional monochromatic images are constructed for different cometary species and the continuum. An original method for the dust continuum glow and gas emissions separation is worked out. Images of the emission spatial distribution of the cometary atmosphere are obtained. The strongest are the emissions of OH (considered here in details), C 2, CN, C 3 and CH. The neutral gas production rate and quantities describing their spatial distribution are determined by the measured intensities (Q OH ∼ 8×1029 mol/s). Results show strong anisotropic distribution of the dust and gas emission with the decreasing of the VEGA-comet distance. The hypothesis of jets structures origin near the nucleus is affirmed for the radicals and the dust continuum. A tomographic reconstruction of the dust continuum distribution around the nucleus is made. A model of isotropic and anisotropic dust ejection can approximately describe it. Two strong jets and dust shells are obtained.

Study of the halley comet near tail glow by Vega-2 three-channel spectrometer data from 10 March 1986

Two-dimensional intensity distributions of the dust continuum, the neutrals and the CO + ion at comparatively undisturbed conditions, taken on 10 March 1986 are applied in order to investigate the near tail of the Halley comet region. Data from the three-channel spectrometer on board Vega-2 are used. An overall decrease of the dust continuum intensity profile with a gradient -.86±.21 is obtained. Superimposed maxima are observed, probably resulting from the dust jets and the nucleus rotation. Such behaviour is not observed in the OH and C 2 distributions. The neutrals' intensity decreases with the increase of the distance to the nucleus. The mean CO + ion velocity is estimated to lie in the interval from -100 to -140 km/s, on the basis of the (3,0) band form and some band intensity ratios. The presence of spatial (possibly dust) sources at distances about 2×10 5 km from the nucleus is affirmed and noticeable changes in the scales of the order of 10 minutes are observed in the CO + distributions.

Energy dissipation by internal stresses in a free-rotating symmetric ellipsoid: Application to Comet P/Halley

Internal stresses dissipate energy in a rotating body, unless it spins about one of its principal axes. If the body is rotating around a non-principal axis, its major-inertia axis and its angular velocity will be nutating about the constant vector of angular momentum. In the course of time, the half-angles of the appropriate precession cones will be slowly shrinking due to dissipative effects. In this way, the body will be approaching the state of minimal kinetic energy. We establish here expressions for the components of the stress tensor in the case of a symmetric ellipsoid continuum body, which is a more suitable shape than the rectangular prism studied in earlier works. Using classical expressions of linear elasticity, we obtain the strain energy per unit volume and the temporal average of the total strain energy. In our model, the relative contribution from the double-frequency mode to the inelastic-dissipation effect is larger than the contribution established by Lazarian & Efroimsky (1999), Efroimsky & Lazarian (2000), and Efroimsky (2001) for a prism. We come up with an expression for the relaxation time and compare it with similar expressions previously derived in the literature. In terms of the overall intensity of the effect, our result is in between the result derived in Lazarian & Efroimsky (1999), Efroimsky & Lazarian (2000), and Efroimsky (2002) and that in Burns & Safronov (1973). We apply our model to the comet P/Halley. Following the model proposed by Belton et al. (1991) for the rotation of Halley's comet, we estimate a relaxation time of 10 2 to 10 4 million years depending on the quality factor assumed.

천년 전의 별똥비

별똥에는 분산 별똥(sporadic meteors)과 별똥비(meteor shower)에 속하는 별똥이 있다. 우리는 <TEX>$\ulcorner$</TEX>고려사<TEX>$\lrcorner$</TEX> <TEX>$\ulcorner$</TEX>천문지<TEX>$\lrcorner$</TEX>에 적혀 있는 별똥 기록을 조사하여 10세기에서 14세기까지 지구 공전 궤도 상의 별찌(meteoroids)의 분포에 대해서 연구하였다 먼저 <TEX>$\ulcorner$</TEX>고려사<TEX>$\lrcorner$</TEX> 에 나오는 별똥 기록의 간지날짜를 점검하여 교정하고 간추려서 자료를 만들었다. 별똥이 나타난 날짜를 조사하여 고려 시대의 별똥별의 특징을 살펴보았다. 고려 시대 별똥 기록은 각 시기에 유행한 철학 사조의 영향과 전쟁과 내란 등의 영향으로 기록 수가 변하는 것으로 추정하였다. 그러나 평소에 떨어지는 분산 별똥들의 계절적 개수 변화는 매우 자연스러웠다. 우리는 일년 중 특정한 날짜에 별똥별이 많이 떨어지는 시기가 몇 개 있음을 발견하였다. 우리는 이것을 별똥비로 보고, 한국<TEX>$\cdot$</TEX>일본<TEX>$\cdot$</TEX>중국<TEX>$\cdot$</TEX>아랍<TEX>$\cdot$</TEX>유럽의 역사 기록에 나오는 별똥 소나기 기록을 모두 조사한 다음, 이것을 <TEX>$\ulcorner$</TEX>고려사<TEX>$\lrcorner$</TEX>의 별똥 기록에서 구한 별똥비와 비교하였다. 우리는 뚜렷한 별똥비 셋과 약한 별똥비 서넛을 확인할 수 있었다. 뚜렷한 세 별똥비는 사자자리 별똥비, 페르세우스 별똥비, 핼리혜성이 남기는 두 별똥비 등의 요즘 별똥비와 각각 일치함을 알아냈다 또한 나머지 약한 별똥비들도 오늘날 관측되고 있는 약한 별똥비와 대체적으로 일치함을 보았다. 결론적으로 고려시대의 별똥비의 활동성은 오늘날의 그것과 크게 다르지 않았다. 이것은 오늘날 활발한 별똥비들의 수명의 하한을 주는 결과이다. 이러한 연구를 통해 별똥 관측에 있어서 우리나라 옛 사람들이 남긴 관측 기록은 실제 자연의 모습을 그대로 읽어낼 수 있을 정도로 꾸준하고 정밀하고 정직한 것이었음을 알 수 있었다. 또한 그러한 좋은 유산을 현대 천문학에 유용한 연구 자료로서 활용할 수 있었다. The spatial distribution of meteoroids or cometary debris along the orbit of the Earth is investigated by analyzing the meteoric records in the Chronicle of the Koryo dynasty (918-1392) which is called Koryosa. Sporadic meteors in this period show the seasonal variation in number, which is similar to the current meteors. We also found that there are a few spikes showing large accumulation of records around the same dates. We regard these spikes as meteor showers in the Koryo period. We compared the dates of meteor showers with those compiled from the historical records around the world including Korea, Japan, China, Arab, and European countries. We discovered three prominent showers and four weak showers. The prominent ones are the Leonids, the Perseids, and the Aquarids and the Orionids pair. The last pair is the remnants of Halley's comet. The astronomical records written in the history book of the Koryo dynasty are turned out to be accurate and written in a steady manner. We can also see that those records can be useful to contribute the development of modern astronomy and astrophysics.

The mechanics and origin of cometaria

The cometarium, literally a mechanical device for describing the orbit of a comet, had its genesis as a machine for illustrating the observable consequences of Kepler's second law of planetary motion. The device that became know as the cometarium was originally constructed by J T Desaguliers in 1732 to demonstrate, in a sensible fashion, the perihelion to aphelion change in velocity of the planet Mercury. It was only with the imminent, first predicted, return of Halley's comet in 1758 that the name cometarium was coined, and subsequent devices so named. Most early cometaria used a pair of elliptical formers joined via a figure-of-eight cord to translate uniform drive motion into the non-uniform motion of an object moving along an elliptical track. It is shown in a series of calculations, however, that two elliptical former cometaria do not actually provide a correct demonstration of Keplerian velocity variations and nor do they actually demonstrate Kepler's second law of planetary motion.

Comets, meteors, and eclipses: Art and science in early Renaissance Italy

Abstract— We discuss eight trecento (fourteenth century) paintings containing depictions of astronomical events to reveal the revolutionary advances made in both astronomy and naturalistic painting in early Renaissance Italy, noting that an artistic interest in naturalism predisposed these pioneering painters to make their scientific observations. In turn, the convincing representations of their observations of astronomical phenomena in works of art rendered their paintings more convincing. Padua was already a renowned center for mathematics and nascent astronomy (which was separating from astrology) when Enrico Scrovegni commissioned the famous Florentine artist Giotto di Bondone to decorate his lavish family chapel (ca. 1301–1303). Giotto painted a flaming comet in lieu of the traditional Star of Bethlehem in the Adoration of the Magi scene. Moreover, he painted a historical apparition that he recently had observed with a great accuracy even by modern standards: Halley's comet of 1301 (Olson, 1979). While we do not know the identity of the artist's theological advisor, we discuss the possibility that Pietro d'Abano, the Paduan medical doctor and “astronomer” who wrote on comets, might have been influential. We also compare Giotto's blazing comet with two others painted by the artist's shop in San Francesco at Assisi (before 1316) and account for the differences. In addition, we discuss Giotto's pupil, Taddeo Gaddi, reputed to have been partially blinded by a solar eclipse, whose calamity may find expression in his frescoes in Santa Croce, Florence (1328–1330; 1338?). Giotto also influenced the Sienese painter Pietro Lorenzetti, two of whose Passion cycle frescoes at Assisi (1316–1320) contain dazzling meteor showers which reveal that the artist observed astronomical phenomena, such as the “radiant” effect of meteor showers, first recorded by Alexander von Humboldt in 1799 and accepted only in the nineteenth century. Lorenzetti also painted sporadic, independent meteors, which do not emanate from the radiant. It is also significant that these artists observed differences between comets and meteors, facts that were not absolutely established until the eighteenth century. In addition we demonstrate that artistic and scientific visual acuity were part of the burgeoning empiricism of the fourteenth century, which eventually yielded modern observational astronomy.

Trailing Halley's Comet: Transforming Science, Mathematics, and Technology Education Through Interdisciplinary Collaborations in Higher Education

Trailing Halley's Comet: Transforming Science, Mathematics, and Technology Education Through Interdisciplinary Collaborations in Higher Education

A Twice-Told Tail: Reinaldo Arenas's “El Cometa Halley”

This essay analyzes the articulation of transgressive desires in Reinaldo Arenas's “El Cometa Halley,” a parodic continuation of Federico García Lorca's La casa de Bernarda Alba. I argue that by moving the Alba sisters from Spain to Cuba and liberating their repressed sexualities, Arenas pursues his fantasies of sexual freedom. Linking his rewriting of García Lorca to the historically significant arrival of Halley's comet in 1910, Arenas relies on the comet's phallic tail to set the story in motion. More specifically, “El Cometa Halley” sketches a preoedipal fantasy of mother-son incest that recurs in Arenas's life and work.

Centaurs - can they enrich the halley type comets population ?

2060 Chiron (95P/Chiron) is the first known object of the entire class called Centaurs. Since the day of the discovery many papers have discussed its past and future fates. Up to now, Centaurs were perceived as a evolutionary stage between Kuiper Belt Objects and the Jupiter Family comets. Other types of dynamical evolution were not widely discussed in previous works. This paper shows there is a possibility that Chiron's and other Centaurs present orbits can evolve into Halley Type comets orbits and this type of dynamical evolution is significant.

A PREVIOUSLY UNLISTED MANUSCRIPT OF THE LATIN "BRUT" CHRONICLE WITH SHERBORNE CONTINUATION

This article has three aims. First, it seeks to advertise the existence and establish the provenance of a previously unlisted manuscript of the Latin prose Brut chronicle, which may be added to the nineteen recently catalogued by Lister Matheson.1 This manuscript, Cambridge, Trinity College, MS R.7.13, fols 1^sup r^-50^sup v^ (hereafter T), is the second to come to light in which the Brut is continued from 1437 to 1456 with material concerning the Benedictine abbey of Sherborne in Dorset. In content it is essentially identical to the other manuscript with a Sherborne continuation, British Library, MS Harley 3906 (hereafter H), variations consisting of a few words at most.2 It will be shown that T was copied from H, and that both have a Sherborne provenance. Secondly, a brief review of the contents of T, and by extension H, and an indication of the sources used in their compilation, will be provided as a contribution to the classification of Latin Brut manuscripts generally. The character of the Latin Brut has never been adequately defined,3 and the material presented here is intended to shed light on the problem in so far as the two manuscripts with a Sherborne continuation are relevant to it.4 Thirdly, a brief discussion of the relationship between T and H, an issue that naturally arises given their similarity, will be included, both for its bibliographical interest and for what it reveals about ownership of the Latin Brut in a medium-sized Benedictine house during the later fifteenth century.5 Charles Kingsford thought the Sherborne appendix to H, in common with other localized continuations of the Latin Brut, unique, 'written with no other object than to bring the particular copy ... a little more up to date'.6 That there were multiple copies is further evidence of the interest that Sherborne's monks had in the history of their institution, and its place in a broader historical spectrum. This historical awareness is also manifest in other surviving late-medieval manuscripts from the monastery, and in the vault paintings of the now-destroyed chapter house, which John Leland tells us represented bishops of Sherborne.7 The short continuations of T and H are, however, the only surviving examples of domestic historiography proper produced at the monastery.T was noted a century ago by M. R. James in his catalogue of Trinity's manuscripts.8 He listed it as 'Chronicon' but did not describe it, and this, along with its unusual (for a Brut) opening ('Adam pater generis humani genuit Seth qui genuit Enos ...'), may explain why it has been overlooked. Following T is a copy of the second recension of William of Malmesbury's Gesta pontificum (fols 58^sup r^-186^sup r^), of which the fifth book is omitted for want of space.9 Although the Gesta pontificum was completed in a post-medieval hand, its first two books are by the scribe of T. The deliberate (and unique) combination of these texts is also a declaration of their difference; R.7.13 was, like other manuscripts containing the Latin Brut (Lambeth Palace, MS 99, for example), planned as a historical compendium incorporating the essentials of both secular and religious history. On the recto of the fourth flyleaf is the beginning of what may have been intended as another Latin Brut (it contains part of an abridgement of the Albina prologue) written in a different but broadly contemporary hand.10 This is not continued on the verso, however, and thus it cannot be regarded as a further, fragmentary Brut manuscript.11 On the fifth flyleaf are two post-medieval notes, the first describing the Brut as 'Epitome Chronicae Angliae', the second identifying it as the work of John de Taxter (a thirteenth-century monastic historian of Bury St Edmunds), the latter an error corrected by a subsequent reader. Although T was copied from [Hamiltonian (script capital H)], it seems unlikely to have been written long after 1456, for it breaks off at the same point (with the appearance of Halley's Comet) despite the provision of four blank leaves for further updating of the text. …

Periodic variation of Oort Cloud flux and cometary impacts on the Earth and Jupiter

Time variation in impact probability is studied by assuming that the periodic flux of the Oort Cloud comets within 15 au arises from the motion of the Sun with respect to the Galactic mid-plane. The periodic flux clearly shows up in the impact rate of the captured Oort Cloud cometary population, with a phase shift caused by the orbital evolution. Depending on the assumed flux of comets and the size distribution of comets, the impact rate of the Oort Cloud comets of 1 km in diameter or greater is from 5 to 700 impacts Myr−1 on the Earth and from 0.5 to 70 impacts per 1000 yr on Jupiter. The relative fractions of impacts are 0.09, 0.11, 0.26 and 0.54 for long-period comets, Halley type comets, Jupiter family comets and near-Earth objects, respectively. For Jupiter, the corresponding fractions in the first three categories are 0.18, 0.31 and 0.51. If we consider physical fading of comet activity that is compatible with the observations, then the impact rates of active comets are two orders of magnitude smaller than the total impact rates by all kinds of comets and cometary asteroids of size 1 km or greater.

Hamlet Rides among the Seminoles

In 1835 Halley's Comet entered into view from earth, as it does every seventy-six years or so, or about once in the lifetime of most men and women. For Europeans, the comet's appearance confirmed the rational, mechanistic order of the universe. Edmund Halley had first charted its broad orbit around the sun in