Any contemporary manual of celestial mechanics contains such notions as “Kepler's Laws”, “Kepler's Equation”, “Keplerian motion”, “Keplerian orbits”, etc. Celestial mechanics before Kepler belongs to the province of history, but modern theoretical astronomy is based on his fundamental investigations.The main work by Kepler appeared in 1609; it was entitled The New Astronomy. Ten years later Kepler published The Harmonies of the World and The Epitome of Copernicus' Astronomy; and in 1627 his famous Rudolphine Tables. These works presented the solution of the mystery of the planetary motions within the limits of the two-body problem; Kepler's success was due to new methods in research.The motion of the planets was found by Kepler to follow three laws: (1) The orbit of each planet is an ellipse, with the Sun as its focus. (2) Each planet revolves so that the line connecting it to the Sun sweeps through equal areas in equal time-intervals. (3) The squares of the periods of any two planets are in the same proportion as the cubes of their mean distances from the Sun.Kepler realized that his laws were approximate. Thus, for example, the motion of the Moon showed a number of irregularities, many of them great enough to have been discovered by ancient astronomers. Such anomalies in the Moon's motion presented the first test of Newton's theory of motion, and his law of gravitation, from which Kepler's laws are deducible, gave a rational and unifying explanation of them.
The Chinese and Japanese records are our primary evidence of the supernova of 1054. But their evidence is not entirely consistent, and recent scholarly discussion of them has not yielded clear-cut results. We have therefore re-examined the original sources in some detail in order to determine their relative historical value and to arrive at as close a determination as possible of the appearance of the event itself. We have established from the Chinese sources that, on the authority of the Chief of the Astronomical Bureau at K'ai-feng, a guest star was first sighted between 9 June and 7 July 1054 to the north-west of ζ Tauri; it became as bright as Venus, was visible in daylight for 23 days and did not disappear from sight until just before 17 April 1056. All this location, duration and brightness data points to this guest star as the supernova progenitor of the Crab nebula. When the Japanese texts are considered the date 4 July 1054 emerges as the most likely date of the first sighting of this supernova. Recent claims for both Middle-Eastern and Western European records are evaluated in the light of this result.
One of the focal points in the intercourse between civilizations was the year + 1267, when the Persian astronomer Jamāl al-Dīn was sent by the Ilkhan from the Marāghah Obervatory to confer with the astronomers of the observatory at Peking directed by Kuo Shou-Ching. The dynastic history of the Yaun preserves accounts both of the designs or models of instruments which the Persian brought with him, and of the instruments which Kuo Shou-Ching set up about the same time. It is suggested that the “Simplified Instrument,” essentially identical with the equatorial mounting of modern telescopes, was Kuo Shou-Ching's modification of the earlier mediaeval Arabic and European instrument known as the torquetum. It was called “simplified” because the ecliptic components had been removed, in accordance with the system of equatorial co-ordinates, classically Chinese, and adopted generally in the West after the time of Tycho Brahe.
This paper describes the progress which has been made on the preparation of a book dealing with the history of Irish astronomy. Due to the disproportionally large amount of material available from the middle of the eighteenth century onward, it has been decided to deal initially with the period from 1780, and accounts are given of nine of the more important observatories founded throughout the country following this date. Each account contains a list of the most outstanding observing instruments possessed by these individual centres, taking into account the period at which they were acquired and a mention of the most noteworthy contributions made to Science by their astronomers. Reference is also made to the important role played by the internationally known Irish telescope makers, Thomas and Howard Grubb, in supplying many of these observatories with equipment of the highest quality.
The rapid construction of American observatories began in the third and fourth decades of the nineteenth century following several earlier, unsuccessful attempts to construct a permanent observatory. After the year 1830 or so, observatories were built in increasing numbers by private individuals, colleges, communities and the Federal government.Interest in the study of this period arises both from the eventual success of the general movement which led to some notable observatories, as well as from the dramatic failures which illustrate the reception of this basic science in early nineteenth-century America. In some instances failure resulted from the reliance on a community's financial support which ended with the loss of scientific control of an observatory's activities. Financial support from communities, however, was also responsible in large part for the magnitude of productive observatories where invariably the control of public supported equipment rested among an educational institution or professional astronomers.The American observatory movement developed at first independently of the Federal government primarily because the majority of congress interpreted the Federal constitution as prohibiting direct aid to foster the sciences.
The vertical motion of matter in two dark filaments observed on 1984 October 26 is studied by measuring the Doppler shift of Hα and the CaII K lines. Measured velocities in a small young filament (filament A) range from 5.5 (downward) to −3.2 kms−1 (upward) in Hα, while in the CaII K line, from 3.1 to −3.8 kms−1. A long-lived filament (filament B) shows the motion of velocities between 4.7 and −3.0 kms−1 in Hα and between 2.9 and −3.2 kms−1 in the CaII K line. The mean values of vertical motion in the filaments A and B measured in Hα are 0.9 and 0.7 kms−1, respectively, and indicate a slight downward motion of the overall filament matter. However the velocities measured in Hα are not always consistent with those in the CaII K line. The two dimensional distribution of vertical velocity in both filaments is studied.
The area of intelligent multimedia (intellimedia) involves the real-time computer processing and understanding of perceptual input from speech, textual and visual sources and contrasts with the traditional display of text, voice, sound and video/graphics with possibly touch and virtual reality linked in. This is the newest area of multimedia research which has seen an upsurge over the last two years and one where many universities internationally do not have, or have not integrated, such expertise.The Institute of Electronic Systems (IES) at Aalborg University, Denmark has initiated a programme in intellimedia under the Multimodal and Multi-media User Interfaces (MMUI) initiative (see for further details). The initiative includes implementation of educational MMUI (M.Eng./Sc., Ph.D.), production of real-time MMUI demonstrators, and establishment of a strong technology-based group of MMUI experts. The Institute has a strong tradition within research activities which fit into the real-time processing of intellimedial systems. Such initiatives will ensure the position of Denmark and the European Union (EU) in the construction of the future of SuperinformationhighwayS.
The observations of the radiation at 21·1 cm wavelength, emitted by interstellar hydrogen, are discussed. These observations, made mostly by Muller in the Netherlands and discussed by Van de Hulst, Muller, and Oort, show that the interstellar clouds are confined to spiral arms that can be traced to distances that were inaccessible to investigations at the wavelengths of light. From these observations also the velocity of rotation of the galactic system at different distances from the galactic centre could be determined, as well as the distance of the Sun from the centre. The temperature of the interstellar clouds was estimated to be about 100° and their average density in the galactic plane to be about 0·9 hydrogen atoms per cubic centimetre.
We have collected all the available observations of blazar OJ 287 published by the end of 1992. OJ 287 has all the characteristics of blazars, but it also exibits some unusual behaviour that has not been observed in other blazars, for example the reported periodic variability, with periods ranging from tens of minutes to tens of years. In this article the observations of OJ 287 are described and are discussed in terms of current blazar models.
We present observations of the FRI radiogalaxy 3C66B during a joint EVN-MERLIN session in May 1995. The jet has been mapped from the 5 mas scale up to about 3 arcmin. The newly mapped VLBI jet shows two elongated blobs in the direction of the brightest kpc jet (NE). We interpret these two blobs in the light of a new model for VLBI jets, making use of the two-fluid concept.
3D, the new MPE NIR imaging spectrometer, provides us with a unique opportunity to probe in detail the structure of the stars, ionized gas, and hot molecular gas in the very centers of AGN. The instrument delivers data cubes with 16×160.5″ pixels which are 256 spectral channels deep. Thus, in a single observation we are able to obtain data on the entire K-Band over an 8″ × 8″ field of view, with a spectral resolution of . In this paper we detail the working principles behind the instrument, and show first results from observations of the inner regions of the Seyfert 1 galaxy NGC7469 made at the Calar Alto observatory.
Both the high nitrogen content of W50 and the fact that SS433 is a binary are consistent with a scenario in which these objects were formed by the explosion of a massive WN star.Attention is drawn to a deficiency of OB stars near the centres of the 38 presently known optical supernova remnants. It is suggested that this deficiency is due to the explosion of the OB stars that formed these SNR's.Beams having a velocity ∼ c/3 would be required to excavate the morphologically peculiar supernova remnant CTB 80 that object was formed by the supernova of 1408.
It is argued from the stationary optical and I.R. spectrum, absolute luminosity and the optical light- and radial-velocity curves, that the SS 433 system consists of a luminous early-type star which is overflowing its Roche lobe , together with a large luminous accretion disk. Both components have roughly similar luminosities. The star transfers mass to the disk at a rate of some 10−4 M⊚/yr. The entire system is embedded in a dense spherically symmetric outflowing atmosphere, resembling that of a Wolf-Rayet star; the outflow velocities are ∼ 1 − 2 × 103 km/sec and the wind mass loss rate is . The presence of the beams suggests that the object at the center of the disk is a neutron star or a black hole.Various possibilities for the evolutionary state of the system are examined. Although the possibility that the compact object is young (∼ 104 yr) cannot be excluded (in which case the progenitor should have been a binary with initial mass ratio very close to unity), it appears more likely that the system is a later evolutionary state of a massive X-ray binary. This would imply that W50 was entirely produced by the beams.
An extraordinary new X-ray source has been discovered with the Einstein Observatory. The source exhibits many parallels with SS 433 and its related SNR, W50. Preliminary results on the associated radio structure observed with the VLA at 20 cm and 6 cm are also presented. The observations are discussed in terms of a precessing beam model.
A model for the generation of the observed intrinsic linear polarization in the optical radiation from SS 433 due to scattering from free electrons in highly ionized material in a jet or inclined disk is examined and compared with observational data. Expressions for the Stokes parameters of the linear polarization as a function of phase are obtained for a simple jet model in which continuum light from a point source is singly scattered by free electrons located along the jets resulting in strikingly different relations between Q and U at different values of model parameters. Comparison of 30 broadband linear polarization measurements with the model indicates a mean value of rotation axis inclination to the line of sight of 63 deg, which is not inconsistent with X-ray and radio data. The measurements are also compatible with models invoking highly inclined disks or rings with emission arising in regions on opposite sides of a diameter.
Results are presented from observations of bright points at a wavelength of 6-cm using the VLA with a spatial resolution of 1.2 arcsec. During two hours of observations, 44 sources were detected with brightness temperatures between 2000 and 30,000 K. Of these sources, 27 are associated with weak dark He 10830 A features at distances less than 40 arcsecs. Consideration is given to variations in the source parameters and the relationship between ephemeral regions and bright points.
Léon Foucault's serendipitous development of the silvered-glass reflecting telescope is described. Foucault's largest mirror had an 80 cm diameter and was installed under the clear skies of Marseilles in 1864. The story of this telescope's hundred years of service is sketched out; famous observers with the instrument were Stéphan, Fabry and Jonckheere.
A study is here made of one of the most remarkable pieces of organized field research in the early middle ages — the meridian survey directed by a Buddhist monk I-Hsing and an official astronomer Nankung Yüeh in +725. At a central chain of four stations in Eastern China, at measured distances apart, covering some 200 km., observations were systematically made. It is believed that these consisted of the measurement of solstitial and equinoctial Sun shadows and of polar altitudes. The observations were also carried out at a chain of five further stations, about 2500 km in length in all, from Indo-China to the southern border of Mongolia. A single northernmost station in the vicinity of Lake Baikal had also been the scene of similar observations, thus making it possible to consider an arc of no less than 3800 km. length. The ratio of terrestrial distance units (li) to the degree, which it was one of the objects of the survey to ascertain, fixed a civil unit in a manner prefiguring the metric system of a thousand years later. The fact that I-Hsing, Nankung Yüeh and their colleagues accepted this ratio as a constant may imply that some of them envisaged the Earth's sphericity—a view in harmony with some of the ancient schools of Chinese cosmology, but not generally accepted by scholars in their time. The li which these astronomers desired to express in terms of the degree appears to have been one of the two usual distance units of the period, namely the “normal short Thang li”. A surprising result is that I-Hsing appears to have had remarkably accurate trigonometric tables at his disposal. The paper concludes with a study of the astronomical standardization of the li by Antoine Thomas S.J. in 1702 at the request of the Khang-Hsi emperor, nearly a century before the similar standardization of the metre in Europe.
Recent experience is helping to sharpen our understanding of how the electronic world differs from the centuries-old, paper-based communication methods. The electronic future is highly interlinked, with all different types of information being included in the web of available resources. The enhanced ability to interchange information electronically improves the effectiveness of communication. At this time the author community does not make full use of the new capabilities. Most astronomers writing for electronic distribution have been slow to adopt new styles of presentation which exploit the new capabilities inherent in the electronic environment. By working together and sharing the burden, the community's resources can be multiplied. A coordinated distributed effort can yield a much more valuable product than any single person or group. Long term archiving and site maintenance are important responsibilities for publishers of electronic scholarly information. Ensuring access to electronic information into the foreseeable future takes planning from the beginning, and requires cooperation between the publishers, libraries, and other scholarly institutions.
The stability of the objective of a long-focus refracting telescope is examined. The coarse-wire objective grating method is applied to the determination of the coma-magnitude scale distortion and magnitude errors. Both of these field errors vary between wide limits and can lead to sizeable positional errors. Grating and direct photographs show a reduction in lens-aberrations with aperture-reducing diaphragms, which is accompanied by a scale-change and modest increase in accuracy at the smaller apertures.Hartmann tests show that the lens requires from 5 to 8 hours to adjust to initial temperature changes at the beginning of a night. The Hartmann method is also applied to the investigation of the variability of spherical aberration, coma, and astigmatism.There are some indications of flexure effects also.
One of the areas which have received a great deal of attention in recent years is the field of the so-called early type peculiar stars. It seems that a review paper on the subject could be of some use, since it helps to visualize both the problems which have been solved and those which have not been solved or studied yet.The present review will not deal, however, with the whole field, but only with one aspect of it, namely the purely spectroscopic side. No attempt is made to cover theoretical aspects, nor explanations of the phenomena observed, since these have been covered in some excellent review papers dealing with either Ap or Am stars or both. The review will deal thus primarily with what one could call “visual spectroscopy”. We hope to demonstrate in the following pages that there is still much room and also much need for this technique. This is due mainly to two facts: first that no two peculiar stars are identical and second that at least some members of the group are spectrum variables. Much confusion has been produced in this field by sweeping generalizations about the behaviour of “all” peculiar stars of a given type, made on the basis of one or two stars analysed in detail. The basic question which is almost never asked is how representative these examples are of the whole group. This is, among others, a task of “visual spectroscopy”, to select typical representatives from the study of large samples. Only then can individual stars be studied profitably and the results generalized for the whole group which they represent.Our subject will be subdivided into four parts. The first will deal with Ap stars, the second with Am stars and the third with Bp stars. This arrangement permits us to deal first with the stars for which we know most and proceed then to less-known stars. The fourth and last part will deal with the conclusions.
The Canary Island observatories are two of the most studied astronomical sites in the world. Half the nights are photometric, most time is usable. Seeing is excellent and there are tentative indications that it is to some extent predictable. Atmospheric transmission is usually good, and well-behaved when it is not. Water vapour is low and well-behaved. Night-sky brightness is low. The paper summarises quantitative data on the above topics.
We present subarcsecond MERLIN 21cm neutral hydrogen absorption line measurements of a 4 × 3 arcseconds (300 × 200 pc) region associated with the active nucleus of the Sc galaxy NGC3079. Broad (200–400 km s−1) and deep (τ ∼ 0.5–1) absorption is seen over much of the region, corresponding to column densities as high as 3 × 1022 atoms cm−2. The absorption shows a velocity gradient which could be consistent with rotation about a central mass of ∼ 109M⊙, however significant non-circular motions are also present which may be due to gas motions in a non-axisymetric potential.
The NASA ADS Astrophysics Science Information and Abstract Service (ASIAS) is enhancing its presence on the WWW by incorporating additional sources of abstracts and making available on-line journal articles. In order to provide more complete coverage of our abstract database, we have started using several sources of astronomical references including NASA/STI, SIMBAD, author abstracts obtained directly from journals, and individual contributions. We are also planning to include abstracts from other subject categories loosely related to astronomy (such as spacecraft instrumentation and communication satellites). Our article service, currently providing full-text papers of the Astrophysical Journal Letters from 1975 to the present, will be greatly expanded to include most of the major astronomical journals, creating one of the first implementations of a digital library for astronomers.
The Astrophysics Science Information and Abstract System (ASIAS) is sponsored by NASA to make astronomical data and literature references available to the astronomical community. It provides access to abstracts, full article images in bitmapped form, and catalog and archive data through the World Wide Web. These services are accessible through the ADS Data Services page at http://adswww.harvard.edu/ads_services.html.
: Chemical Evolution of the Galaxy. The closed system model and its limitations. For a closed system, where the sum of gas and matter contained in stars is constant at any time, one derives a simple set of equations which relate the enrichment (or depletion) of the interstellar matter (ISM) to the gas-to-total mass ratio, if a power-law dependence of the star formation rate (SFR) on the total mass of gas, is adopted. We apply the predictions of the closed system for k=1 to the galactic disk. Reasonable agreement is obtained for the chemical evolution of the ISM in the solar vicinity, but the model completely fails to explain both the observed galactic abundance gradients, and the observed time variation of the chemical evolution.
The method of classical fine-analysis of early-type spectra is outlined and results are discussed. Normal OB-star atmospheres have essentially solar composition, apart from neon which is overabundant. The CNO ratios might also deviate. The helium abundance is . Peculiar stars are briefly considered.
The abundances of the light elements, especially Li and Be, are key diagnostics of stellar structure and evolution in cool stars because they are readily destroyed by nuclear reactions in stellar interiors. Reactions with protons destroy Li at ∼2.5×106 K and Be at ∼3.5 × 106K. The sun has destroyed almost all of its original Li but none of its Be during its main sequence lifetime. Other main sequence stars have lost both Li and Be, some have lost only a small amount of Li. Thus the present abundances provide sensitive probes into the envelopes of stars. Recent results on Li and Be in F and G dwarfs in galactic clusters and in the field are highlighted.As stars evolve toward the red giant phase, the outer envelopes expand and the observed light element abundances are diluted as the surface material containing Li and Be are mixed with material from deeper layers which is devoid of Li and Be. However, some carbon and S stars have an extremely strong resonance line of Li I, while others have virtually no Li. New observations of such stars are presented.
We discuss the mechanism of particle diffusive acceleration by shocks developed by non-linear fluid instabilities in collimated flows as the basis of a model to interpret the synchrotron brightness distribution and spectrum of extragalactic jets. Predictions for future VLBI observations are derived.
The acceleration of solar flare γ-ray producing protons by Alfven mode turbulence is addressed. We improve on previous modelling of this process by allowing the turbulent energy density to decline as the proton energy density increases. Thus some discussion of the time-dependent behaviour of the accelerator is possible. The γ-ray line spectra, timing and absolute intensities place constraints on parameters of the accelerator. In particular, we find that the acceleration region must comprise most of the flaring corona.
The rapid development of world-wide networking during the last two years, due partly to the simple concept of addressing with uniform resource locators (URLs), has drastically simplified information exchange. This expanding communication media has created new possibilities in the access of large databases, and has therefore found a particular interest in astronomy. The most used means of information transfer is text. If large sets of multi-dimensional data, commonly images, have to be accessed, longer transfer times compared with text urge the data manager to find more efficient solutions. Modern tools are not as efficient at browsing among images through a network compared with browsing text. Either the images being browsed are too large to be transferred quickly, or the image size is reduced so much that the interesting information is lost during the data reduction. In this article, an alternative to the transfer of plain images is investigated, based on the fact that only a part of an image's information content is needed for browsing. Images may therefore be reduced to icons which only symbolically represent the information content. Such image icons are used to browse solar radio spectrograms in the Zurich Radio Astronomy Group archive.
The discovery of the strong Galactic X-ray sources (Giacconi et al., 1962; Giacconi, 1974; Gursky and Schreier, 1975) and the suggestion that these sources may be powered by accretion onto a compact object orbiting a ‘normal’ stellar companion (Hayakawa and Matsouko, 1964; Zel'dovich and Guseynov, 1965) has, over the past twenty years or so, led to renewed interest in the processes of mass transfer and accretion in close binary stars.
The action of Ashtekar gravity have been found by Cappovilla, Jacobson and Dell. It does not depend on the metric nor the signature of the space-time. The action has a similar structure as that of a massless relativistic particle. The former is naturally generalized by adding a term analogous to a mass term of the relativistic particle. The new action possesses a constant parameter regarded as a kind of a cosmological constant. It is interesting to find a covariant Einstein equation from the action. In order to do it we will examine how the geometrical quantities are determined from the non-metric action and how the Einstein equation follows from it. Comment: 6p. Tex
Although the indigenous people of Southern Africa traditionally viewed the sky as a place quite apart from the Earth, they believed celestial phenomena to be natural signs united with those of the Earth in a harmonious synchronicity. There is no substantial evidence that the precolonial Africans imagined a casual relationship between celestial bodies and the seasonal patterns of life on Earth. They did, however, recognize a coincidental relationship. The traditional African cosmos, then, worked as a noetic principle unifying the observed motions of celestial bodies, the sequence of seasons, and the behavior of plants and animals. Such a cosmos, with local peculiarities, was widely understood in Southern Africa before the end of the last century. By the early 20th century European colonial paradigms had largely obliterated this African worldview. This paper will offer a partial reconstruction. Pre-colonial South African people viewed time as a sequence of discrete natural events; through annual repetition these events served as a guide for proper human action. The South Africans analyzed the passage of time in terms of the motions of celestial bodies, the maturation of beneficial plants, and the mating patterns of animals. The rightful course of human life was seen to fit within the seasonal context of these natural phenomena. The visibility of conspicuous stars and asterisms marked significant times of year. For instance, the Lovedu people greeted the dawn rising of Canopus with joy: “The boy has come out.” The star was a signal for rainmaking and boys' initiation ceremonies to proceed. The Venda constellation Thutlwa, the giraffes, comprises α and β Crucis and α and β Centauri. In October Thutlwa skims the trees of the evening horizon. The Venda Thutlwa literally means ‘rising above the trees,’ an allusion to the majestic vegetarian creatures and the stars advising the people to be done with their spring planting. This paper will describe stellar associations with other creatures: wild dogs, warthogs, wildebeests, swallows, cuckoos and cicadas. In each case the visibility of a star will synchronize with a behavior of the associated species. Together, stars and species informed man of the order and unity of an African cosmos — a worldview that must have been as satisfying as it was beautiful.
Astronomical investigation in South Africa begins with the European settlement at the Cape. Observations by visitors, some of whom stayed only very briefly, were mainly concerned with the determination of the geographical position of the Cape. The first scientific expedition of importance was that of Lacaille in 1751–1753, who undertook geodesy and positional astronomy. In spite of his enormous services to astronomy, no full-length biography of Lacaille appears to have been written. The early work of the Cape Observatory included a verification and extension of Lacaille's geodetic measurements, undertaken by Maclear. Maclear investigated Lacaille's work very thoroughly, and his papers in the South African Archives, which also deal, among other topics, with the period of John Herschel's visit to the Cape (1834–1838), are probably the major unworked source of historical material on astronomy in South Africa. Related documents exist at the Royal Greenwich Observatory in England, and among the Herschel papers, now dispersed. The later history of astronomy at the Cape is well covered by printed works, notably by those of Sir David Gill. A similar remark applies to the more recent activities of the numerous observatories in South Africa. The possibilities of the investigation of Bantu traditions previous to European settlement are mentioned.
Various lines of evidence indicate that the frequency of meteorite falls has varied greatly in course of time. It seems that glass meteorites fell on our Earth only during the late Tertiary and early Quaternary; that iron and stone meteorites did not fall before the late Quaternary; that centuries ago the fall of iron meteorites was a much more common phenomenon than to-day; and that even since 1800 meteorite falls have become noticeably rarer.
X-ray absorption measurements directly probe the torus in Seyfert 2 galaxies and X-ray reflection studies can reveal that part of the torus which is Thomson-thick in Seyfert 1 galaxies. Current observations of Seyfert 1 however show no evidence for this last component, indicating that the Thomson-thick part of a typical torus covers less than about 30% of the Sky as seen from the central source. ASCA data on more powerful distant objects shows that the torus in the type 2 quasar IRAS P09104 covers about 20% of the Sky and in 2 PG quasars at z ∼ 1 it covers less than about a quarter of the Sky. ROSAT data on radio galaxies helps define the absorption there, indicating that the torus in distant FRII sources exceeds 1023 cm−2. The X-ray Background requires that most of the primary power in AGN is absorbed, thereby giving a dominant role to the torus.
Recent observations of the spectrum of Algol confirm the existence of duplicities in the line profile of Mg II 4481 near the phase of totality. In this article, written in 1953, the suggestion is advanced that the magnesium atoms may be located preferentially in an equatorial belt between ± 50% of latitude.
Evidence relevant to the question of whether or not galaxies in clusters are aligned is reviewed. It is concluded that there is evidence in favour of alignment in some clusters. The most commonly discussed mechanism for the origin of such alignments is that of galaxy formation from cluster pancakes, as proposed by Doroshkevich, Sunyaev and Zel'dovich. However, an alternative mechanism which can in principle lead to alignments, and which in any case is relevant to their secular stability (however produced), is that of tidal forces, as recently discussed by Miller and Smith. These two mechanisms are reviewed. It is concluded that the first is more plausible as an account of the origin of alignments; but that the second has several implications for the dynamics of galaxies in clusters which deserve further study.
The Royal Observatory was founded in 1675 specifically for “… the rectifying the tables of the motions of the heavens, and the places of the fixed stars, so as to find out the so much desired longitude of places for the perfecting the art of navigation.” Ninety-one years later Nevil Maskelyne, the fifth Astronomer Royal, was able to compile The Nautical Almanac and Astronomical Ephemeris for the year 1767 which made possible the determination of longitude at sea to an acceptable precision.The key to the successful solution of this problem is the method of lunar distances, and this method is discussed both historically and scientifically.The objects of this paper are: to examine the contribution to this achievement made by the Royal Observatory and its Astronomers Royal; and to speculate on the reasons for, and the effect of, the adoption of a nominal precision of 1″ (quite unnecessary accuracy) in the tabulations of lunar distances and in the associated calculations.All the main historical events and developments are well-known, and the historical detail has been curtailed accordingly.
In this paper, two ancient Indian texts, the Śatapatha Brāhmana and the Rigveda, are examined for their astronomical content. It is argued that the 95 year ritual of agnicayana had an astronomical basis, which implies a knowledge of the length of the tropical year being equal to 365.24675 days. An astronomical code has been discovered in the structure of the Rigveda, which has been partially deciphered. This code expressed the knowledge that the sun and the moon are about 108 times their respective diameters away from the earth. This analysis leads to a major revision of our understanding of the history of ancient astronomy.
Theoretical and observational methods in astronomy have advanced to a point where certain of their outcomes are difficult to comprehend with the traditional categories of human knowledge. The philosophical discipline of epistemology, the theory of knowledge, is used here to address four current problems in observational astronomy, exobiology, cosmology, and quantum mechanics. The problems are united by an epistemological content which, when unrecognized, has resulted in some heroic solutions of an nature. Immanuel Kant's critical philosophy is employed because his work is consistent with basic attitudes in present-day physics and biology.
High altitude sounding rockets have been used to investigate extra-terrestrial radiations and the properties of the atmosphere. This article surveys the outstanding results achieved in these studies, including: direct measurements of the solar ultra-violet and X-radiation; composition and energy spectrum of the primary cosmic rays; the incidence of micrometeorites; the dependence on altitude up to 220 km of atmospheric pressure, density, temperature, and composition; the distribution of ozone with height; evidence on the intensity and origin of the day airglow; the electron and ion density distribution in the ionospheric layers up to 350 km; variation of the Earth's magnetic field with altitude; evidence on the location of ionospheric current sheets and conclusions about the conductivity of the ionosphere; high-altitude photography and its applications.Characteristics are given of high altitude sounding rockets used in the U.S.: V-2, Aerobee, Viking, and Deacon. Suggestions are made for overcoming some of their inherent limitations to allow an expansion of possibilities for high altitude studies. Arguments are presented for the usefulness of instrumented artificial satellite rockets for astrophysical research.
The very large overabundances of rare earth elements found in Ap stars (>103 − 105) usually arise in cases where the observable second spectra does not represent the dominant ionization stage. The extreme overabundance factors are highly correlated with effective temperature in a way that is regarded with suspicion. In cool Ap stars, where one does observe the dominant ionization state, more modest overabundances (∼ 102) occur. The typical cool Ap and Am stars must have abundances of the lighter lanthanides. It is argued that the sharp rise in typical Ap star abundances that parallels the predicted degree of ionization may be due to a breakdown in the Saha Equation or possibly to the existence of a cool upper photosphere caused by line blanketing in the hotter Ap stars.Attention is called to the observational fact that the cool Am stars have deeper line cores than chemically normal main sequence stars or cool Ap stars. These line cores resemble those of more luminous stars, a fact which comports well with some (though not all) low dispersion similarities between Am stars and evolved objects. While various studies (e.g. by Conti and Van't Veer Menneret) have shown that reduced gravity models cannot remove the abundance anomalies in the Am stars, some modification of the traditional models and/or line formation theory is indicated in order to explain the observations.
SKY Online is the World Wide Web site of Sky Publishing Corporation, publisher of Sky & Telescope magazine. Conceived mainly as an electronic extension of the company's marketing and promotion efforts, SKY Online has also proven to be a useful tool for communication between amateur and professional astronomers.
In this article we review current progress in our understanding of large scale cosmic structure from the analysis of galaxy redshift surveys; in particular we highlight techniques recently developed to reconstruct in full the large scale matter density and peculiar velocity fields, contrasting them with earlier methods of analysis. We discuss the principles on which these new techniques are founded, and describe the practical difficulties encountered in applying them to sparse and noisy data. We summarise the results of reconstructions carried out on recent surveys and indicate some implications of these results for current models of structure formation.
The discovery that a significant number of distant cometary nuclei and icy planetesimals have diameters in excess of 100 km and revolve around the Sun on chaotic orbits with lifetimes in the order of 1 million years, shows that the inner Solar System is subject to the passage of exceptionally large comets with masses ranging from 1000 to 10,000 times that of Halley's comet. The observed cometary flux suggests that the mean interval between the injection of large (d ≳ 100 km) comets into short-period orbits is in the order of 100,000 years, sufficiently short compared with the expected physical lifetime of comets that effects due to fragmentation of the most recent giant comet captured into a short-period orbit might still be observable. The evolution of comets into both Halley-type and Jupiter-family short-period orbits, particularly those passing close to the Sun or Jupiter, is reviewed and the astronomical evidence for giant-comet break-up is presented. Encounters of the Earth with cometary decay products (asteroids, boulders and dust) have important implications for the evolution of life on earth, and on shorter timescales the development of civilization. The existence of streams of cometary debris on Earth-crossing orbits during past millennia would have produced a much more active astronomical environment than that currently observed, with possibly important implications for the study of ancient myths and religions.
The dates for the second (ca. 2700 B.C. to within 250 years) and the third ecliptical quartets (ca. 1200 B.C. to within 400 years) evaluated earlier are considered in the context of ancient Egyptian history. The origin of the second quartet coincides with the Great Pyramids and the initiation of the Egyptian solar, or so-called “civil” calendar, the first of such a type in the world. The third quartet is concurrent with the solar conversion of Amenhotep IV (Akhenaton) and takes place at the finale of the great Sothic period of 1461 years after the initiation of the solar calendar. It is argued that the Great Pyramids seem to be monuments to the Sun-god built in honor of the Egyptians having reached an understanding of the Sun's track upon the starry background, Akhenaton's conversion being in a direct connection with the original Pyramids' ideology. This paper is the third part of a single investigation. The first two parts “On the Origin of the Zodiacal Constellations” and “Prehistory of Zodiac Dating: Three Strata of Upper Paleolithic Constellations” were published in Vistas in Astronomy in 1993 and 1995.