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Journal articles on the topic 'Spherical astronomy'

Author: Grafiati
Published: 4 June 2021
Last updated: 30 July 2024

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1

Inayah, Maulida, and Ahmad Izzuddin. "Universal Solution of Medieval Spherical Astronomy." KULMINASI: Journal of Falak and Sharia 1, no. 2 (October 6, 2023): 1–25. http://dx.doi.org/10.22373/kulminasi.v1i2.4173.

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Spherical astronomy is a part of astronomy that figures of the sky as a sphere. It concerns the study of astronomical coordinate frames, the direction and apparent motion of celestial bodies, the determination of positions from astronomical observations, and the errors that can occur in observations. Spherical astronomy makes it easier for humans to determine the direction and position of celestial bodies relative to observers on Earth. In the history of human civilization, spherical astronomy has been the solution to determining the time of worship for medieval Muslims. Especially during the glory days of the Mamluks, Egypt and Syria. This article was written based on literature research with qualitative method as an approach. Then the collecting data was carried out by the documentation method on various notes, books, transcripts and images could be found. Then the data was analyzed descriptively. The results of this research show that Egyptian and Syrian astronomers during Mamluk reign (between the 13th-15th centuries) made a major contribution to the progress and development of science, especially in astronomy. Both the preparation of astronomical tables and various astronomical tools or instruments they designed.
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2

Gurm, H. S. "Teaching of Astronomy in India." International Astronomical Union Colloquium 105 (1990): 389–93. http://dx.doi.org/10.1017/s0252921100087340.

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Studies of the skies have dominated intellectual activities since ancient man. In this respect, India has a very long tradition of such recorded activity, covering the observations of celestial bodies both as a science and as mythology (Gurm, 1980). The first half of the Christian era witnessed the evolution of spherical astronomy as a part of the study of mathematics (algebra and trigonometry) and its application to astrology. The evolution of spherical astronomy culminated in the concrete manifestation in the northern parts of India in the form of Jantar-Mantars by Raja Jai Singh (Mayer, 1979) in the early eighteenth century. Interestingly, spherical astronomy remained one of the most important activities in the study of astronomy during the British period too. Some of the older treatises on this subject during the nineteenth century were written in the Offices of the Survey of India.
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3

Plofker, Kim. "Spherical Trigonometry in the Astronomy of the Medieval Kerala School." Highlights of Astronomy 11, no. 2 (1998): 722–23. http://dx.doi.org/10.1017/s153929960001858x.

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Although the methods of plane trigonometry became the cornerstone of classical Indian mathematical astronomy, the corresponding techniques for exact solution of triangles on the sphere’s surface seem never to have been independently developed within this tradition. Numerous rules nevertheless appear in Sanskrit texts for finding the great-circle arcs representing various astronomical quantities; these were presumably derived not by spherics per se but from plane triangles inside the sphere or from analemmatic projections, and were supplemented by approximate formulas assuming small spherical triangles to be plane.
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4

Cardoso, Jorge, Décio Martins, Helmuth Malonek, and Carlos Fiolhais. "Manuel dos Reis e a Astronomia em Portugal de 1930 a 1970." História da Ciência e Ensino: construindo interfaces 20 (December 29, 2019): 550–67. http://dx.doi.org/10.23925/2178-2911.2019v20p550-567.

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Resumo Descreve-se a evolução do Observatório Astronómico da Universidade de Coimbra de 1930 a 1970, destacando- se o exercício das funções de diretor por Manuel dos Reis (1900-1992), de 1934 a 1970. Fonte primordial é o espólio documental de Manuel dos Reis à guarda do Arquivo da Universidade de Coimbra, que inclui programas, lições, problemas, exames, estudos e notas, e outros manuscritos sobre História da Astronomia, Astronomia (Geral, Mecânica, Esférica e Geodésica), Astronomia Medieval, e Astronomia Náutica dos Descobrimentos. Engloba ainda listas bibliográficas, rascunhos das comunicações e discursos sobre Astronomia Náutica proferidos na Academia das Ciências de Lisboa. Apresenta-se, em particular, um documento datilografado, inédito, provavelmente da década de 30, com o título “Reorganização do ensino da Astronomia e da investigação astronómica”, onde Reis, após descrever brevemente a história da Astronomia, refere a Astrofísica como o “novo capítulo da Astronomia”, e reflete sobre o ensino e investigação da Astronomia, e sobre o funcionamento dos Observatórios Astronómicos de Coimbra e de Lisboa (Tapada da Ajuda), e do Observatório Meteorológico do Porto (Serra do Pilar).Palavras-chave: História da Astronomia em Portugal; Astrofísica, Observatório Astronómico da Universidade de Coimbra. Abstract The evolution of the Astronomical Observatory of the University of Coimbra from 1930 to 1970 is described, highlighting Manuel dos Reis (1900-1992) role as director from 1934 to 1970. Main source is the collection of Manuel dos Reis documentation in the Archive of the University of Coimbra, which includes programs, lessons, problems, exams, studies and notes and other manuscripts on the History of Astronomy, Astronomy (General, Mechanical, Spherical and Geodesical), Medieval Astronomy, Nautical Astronomy of the Portuguese Discoveries. It also includes lists of bibliographical references, minutes of communications and speeches on Nautical Astronomy delivered at the Academy of Sciences of Lisbon. A typewritten, unpublished document, with the title "Reorganization of the teaching of astronomy and astronomical investigation”, probabbly from the 1930s, is presented. Reis, after a brief description of the history of Astronomy, describes Astrophysics as the "new chapter of Astronomy", reflects on the teaching and research on Astronomy, and on the operation of the Astronomical Observatories of Coimbra and Lisbon (Tapada da Ajuda), and the Meteorological Observatory of OPorto (Serra do Pilar). Keywords: History of Astronomy in Portugal; Astrophysics; Astronomical Observatory of the University of Coimbra.
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5

Faraoni, Valerio. "Turnaround physics beyond spherical symmetry." Journal of Physics: Conference Series 2156, no. 1 (December 1, 2021): 012017. http://dx.doi.org/10.1088/1742-6596/2156/1/012017.

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Abstract The concept of turnaround radius in an accelerating universe is generalized to arbitrarily large deviations from spherical symmetry, as needed by astronomy. As a check, previous results for small deviations from spherical symmetry are recovered.
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6

Luz Pelissari de Oliveira, Christian, and Fernando Pereira de Souza. "TRIGONOMETRIA ESFÉRICA APLICADA NA ASTRONOMIA DE POSIÇÃO." COLLOQUIUM EXACTARUM 10, no. 2 (June 1, 2018): 60–67. http://dx.doi.org/10.5747/ce.2018.v10.n2.e239.

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The present article is the result of a research work of the Degree in Mathematics in the scope of the Tutorial Education Program -PET. The work deals with concepts of Spherical Trigonometry, which has several fields of applications between mathematics and physics, related to cartographic problems, navigation and astronomy. The goal is to explore problems of astronomy applications of celestial bodies by making use of trigonometry concepts in the sphere to study positions and directions of stars in terms of a celestial sphere. In order to reach this objective, the article presents concepts of a smaller distance between two points in the sphere, a triangle of position that is the spherical triangle, the fundamental relation known as law of cosines, the Celestial Sphere, its elements, its coordinates in the equatorial system, horizontal system and time system. Thus, the work seeks to encourage students and teachers to work on Spherical Geometry in the classroom
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7

Firneis, M., and F. Firneis. "On the use of quaternions in spherical and positional astronomy." Astronomical Journal 91 (January 1986): 177. http://dx.doi.org/10.1086/113998.

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8

Loizeau, Nicolas, and Glennys R. Farrar. "Non-spherical dark matter structures detection." Journal of Cosmology and Astroparticle Physics 2022, no. 03 (March 1, 2022): 049. http://dx.doi.org/10.1088/1475-7516/2022/03/049.

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Abstract A rotation curve inequality that holds for spherically symmetric mass distributions is derived, and tested against the SPARC galaxy rotation curves dataset. We identify several Galaxies, e.g. NGC7793 and UGC11557, which are candidates for hosting non-spherical dark matter structures that could be detected by more precise measurements.
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9

Tolchelnikova, S. A., and K. N. Naumov. "On the matter of proving Euclidean fifth postulate and the origin of non-Euclidean geometries." Geodesy and Cartography 950, no. 8 (September 20, 2019): 2–11. http://dx.doi.org/10.22389/0016-7126-2019-950-8-2-11.

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The Euclidean geometry was developed as a mathematical system due to generalizing thousands years of measurements on the plane and spherical surfaces. The development of celestial mechanics and stellar astronomy confirmed its validity as mathematical principles of natural philosophy, in particular for studying the Solar System bodies’ and Galaxy stars motions. In the non-Euclidean geometries by Lobachevsky and Riemann, the third axiom of modern geometry manuals is substituted. We show that the third axiom of these manuals is a corollary of the Fifth Euclidean postulate. The idea of spherical, Riemannian space of the Universe and local curvatures of space, depending on body mass, was inculcated into celestial mechanics, astronomy and geodesy along with the theory of relativity. The mathematical apparatus of the relativity theory was created from immeasurable quantities
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10

Krassovitskiy, Pavel M., and Fedor M. Pen’kov. "Three-Dimension Calculation for the Scattering Problem for Non-Spherical Potential." Physics 6, no. 1 (March 6, 2024): 368–75. http://dx.doi.org/10.3390/physics6010024.

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The interaction of the 238U with a neutron is studied. Correct accounting for the non-spherical shape of the uranium nucleus is in focus. The optical potential is used as a model. It is shown that the spherically symmetric and non-spherical potentials give different scattering patterns, in particular different resonance features of the cross-section. The possibility of using the method as an extension of the particle–rotor model of the nucleus is illustrated.
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11

Bowick, M. J. "Spherical crystals." Journal de Physique IV 12, no. 9 (November 2002): 221–25. http://dx.doi.org/10.1051/jp4:20020399.

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The structure of condensed matter order may change when the medium is curved. This is illustrated for the case of spherical crystals formed by self-assembled colloidal beads on water droplets in oil. Beyond a minimum crystal size novel grain boundary scars proliferate in the ground state.
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12

Kapustin, A. D., and S. A. Paston. "Analytical analysis of the origin of core-cusp matter density distributions in galaxies." Journal of Cosmology and Astroparticle Physics 2022, no. 11 (November 1, 2022): 025. http://dx.doi.org/10.1088/1475-7516/2022/11/025.

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Abstract We propose an analytical method to describe a matter density profile near a galaxy center. The description is based on the study of the distribution function of particles over possible trajectories. We establish a relation between the central slope of density profile and the near-origin behavior of the angular momentum distribution function. We consider both a spherically symmetric (on average) matter distribution as well as deviations from it. If the density profile forms in a background of spherical gravitation potential then a core-type distribution arises. A regular matter may behave in such way if the background potential was formed by the dark matter. In the presence of deviation from spherical symmetry the formation of cusp-type distribution is possible. Moreover, a reduction of spherical symmetry to the axial one leads to a less steep cusp profile. The complete symmetry breaking (which corresponds, in particular, to the common setup of numerical simulations), leads to a steeper cusp profile.
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13

HOUZEL, CHRISTIAN. "THE NEW ASTRONOMY OF IBN AL-HAYTHAM." Arabic Sciences and Philosophy 19, no. 1 (March 2009): 1–41. http://dx.doi.org/10.1017/s0957423909000575.

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In order to get rid of the contradictions he had identified in Ptolemy’s Astronomy, Ibn al-Haytham abandons cosmology and develops a purely kinematic description of the movement of the wandering stars. This description culminates with the proof that such a star, during its daily movement, reaches exactly one time a maximum height above the horizon and that any inferior height is reached exactly twice. The proofs of these facts necessitates new mathematical tools and Ibn al-Haytham is led to establish very sophisticated statements concerning the variation of certain ratios of arcs of circles on the sphere. He also introduces the fruitful idea of assimilating a very small spherical triangle to a plane triangle.
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14

Singh, Sayuri, Dharmanand Baboolal, Rituparno Goswami, and Sunil D. Maharaj. "Gaussian curvature of spherical shells: a geometric measure of complexity." Classical and Quantum Gravity 39, no. 23 (November 10, 2022): 235010. http://dx.doi.org/10.1088/1361-6382/ac9efe.

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Abstract We consider a semitetrad covariant decomposition of spherically symmetric spacetimes, and find a governing hyperbolic equation for the Gaussian curvature of two dimensional spherical shells, that emerges from the decomposition. The restoration factor of this hyperbolic travelling wave equation allows us to construct a geometric measure of complexity. This measure depends critically on the Gaussian curvature, and we demonstrate this geometric connection to complexity for the first time. We illustrate the utility of this measure by classifying well known spherically symmetric metrics with different matter distributions. We also define an order structure on the set of all spherically symmetric spacetimes, according to their complexity and physical properties.
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15

Lei, Kin, Dongxu Qi, and Xiaolin Tian. "A New Coordinate System for Constructing Spherical Grid Systems." Applied Sciences 10, no. 2 (January 16, 2020): 655. http://dx.doi.org/10.3390/app10020655.

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In astronomy, physics, climate modeling, geoscience, planetary science, and many other disciplines, the mass of data often comes from spherical sampling. Therefore, establishing an efficient and distortion-free representation of spherical data is essential. This paper introduces a novel spherical (global) coordinate system that is free of singularity. Contrary to classical coordinates, such as Cartesian or spherical polar systems, the proposed coordinate system is naturally defined on the spherical surface. The basic idea of this coordinate system originated from the classical planar barycentric coordinates that describe the positions of points on a plane concerning the vertices of a given planar triangle; analogously, spherical area coordinates (SACs) describe the positions of points on a sphere concerning the vertices of a given spherical triangle. In particular, the global coordinate system is obtained by decomposing the globe into several identical triangular regions, constructing local coordinates for each region, and then combining them. Once the SACs have been established, the coordinate isolines form a new class of global grid systems. This kind of grid system has some useful properties: the grid cells exhaustively cover the globe without overlapping and have the same shape, and the grid system has a congruent hierarchical structure and simple relationship with traditional coordinates. These beneficial characteristics are suitable for organizing, representing, and analyzing spatial data.
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16

Kerby, L. "Volumetric spherical polynomials." AIP Advances 9, no. 6 (June 2019): 065107. http://dx.doi.org/10.1063/1.5086695.

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17

Gertsenshtein, M. E., and E. Yu Melkumova. "Isotropic spherical coordinates." Soviet Physics Journal 30, no. 4 (April 1987): 338–40. http://dx.doi.org/10.1007/bf00914840.

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18

Dowker, J. S. "Spherical Casimir pistons." Classical and Quantum Gravity 28, no. 15 (July 4, 2011): 155018. http://dx.doi.org/10.1088/0264-9381/28/15/155018.

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19

Koláček, J. "Spherical spin waves." Czechoslovak Journal of Physics 37, no. 1 (January 1987): 8–15. http://dx.doi.org/10.1007/bf01597871.

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20

Kreps, Stanislav, Vladimir Shuvayev, Mark Douvidzon, Baheej Bathish, Tom Lenkiewicz Abudi, Amirreza Ghaznavi, Jie Xu, Yang Lin, Lev Deych, and Tal Carmon. "Coupled spherical-cavities." AIP Advances 12, no. 12 (December 1, 2022): 125022. http://dx.doi.org/10.1063/5.0084815.

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In this work, we study theoretically and experimentally optical modes of photonic molecules—clusters of optically coupled spherical resonators. Unlike previous studies, we do not use stems to hold spheres in their positions relying, instead, on optical tweezers to maintain desired structures. The modes of the coupled resonators are excited using a tapered fiber and are observed as resonances with a quality factor as high as 107. Using the fluorescent mapping technique, we observe families of coupled modes with similar spatial and spectral shapes repeating every free spectral range (a spectral separation between adjacent resonances of individual spheres). Experimental results are compared with the results of numerical simulations based on a multi-sphere Mie theory. This work opens the door for developing large arrays of coupled high-Q spherical resonators.
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21

Lemaitre, Gerard, Pascal Vola, and Eduard Muslimov. "Active Optics in Astronomy: Freeform Mirror for the MESSIER Telescope Proposal." Mathematical and Computational Applications 24, no. 1 (December 27, 2018): 2. http://dx.doi.org/10.3390/mca24010002.

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Active optics techniques in astronomy provide high imaging quality. This paper is dedicated to highly deformable active optics that can generate non-axisymmetric aspheric surfaces—or freeform surfaces—by use of a minimum number of actuators. The aspheric mirror is obtained from a single uniform load that acts over the surface of a closed-form substrate whilst under axial reaction to its elliptical perimeter ring during spherical polishing. MESSIER space proposal is a wide-field low-central-obstruction folded-two-mirror-anastigmat or here called briefly three-mirror-anastigmat (TMA) telescope. The optical design is a folded reflective Schmidt. Basic telescope features are 36 cm aperture, f/2.5, with 1.6° × 2.6° field of view and a curved field detector allowing null distortion aberration for drift-scan observations. The freeform mirror is generated by spherical stress polishing that provides super-polished freeform surfaces after elastic relaxation. Preliminary analysis required use of the optics theory of 3rd-order aberrations and elasticity theory of thin elliptical plates. Final cross-optimizations were carried out with Zemax raytracing code and Nastran FEA elasticity code in order to determine the complete geometry of a glass ceramic Zerodur deformable substrate.
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22

Sari, Re'em, and Peter Goldreich. "Spherical Accretion." Astrophysical Journal 642, no. 1 (April 10, 2006): L65—L67. http://dx.doi.org/10.1086/504152.

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23

Korpinar, Talat, and Zeliha Korpinar. "Spherical magnetic flux flows with fractional Heisenberg spherical ferromagnetic spin of optical spherical flux density with fractional applications." International Journal of Geometric Methods in Modern Physics 18, no. 08 (May 4, 2021): 2150117. http://dx.doi.org/10.1142/s0219887821501176.

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In this paper, we construct a new approach of spherical magnetic Lorentz flux of spherical [Formula: see text]-magnetic flows of particles by the spherical frame in [Formula: see text] spherical space. Eventually, we obtain some optical conditions of spherical [Formula: see text]-magnetic Lorentz flux by using directional spherical fields. Moreover, we determine spherical magnetic Lorentz flux for spherical vector fields. Also, we give new construction for spherical curvatures of spherical [Formula: see text]-magnetic flows by considering Heisenberg spherical ferromagnetic spin. The approximate solution is expressed by a table and some graphics. Finally, the magnetic flux surface is demonstrated in a static and uniform magnetic surface by using the analytical and numerical results.
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24

Fang, Cheng. "Past, Present and Future of Chinese Astronomy." Proceedings of the International Astronomical Union 10, H16 (August 2012): 19–29. http://dx.doi.org/10.1017/s1743921314004621.

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AbstractThrough out the ancient history, Chinese astronomers had made tremendous achievements. Since the main purpose of the ancient Chinese astronomy was to study the correlation between man and the universe, all the Emperors made ancient Chinese astronomy the highly regarded science throughout the history. After a brief introduction of the achievement of ancient Chinese astronomy, I describe the beginnings of modern astronomy research in China in the 20th century. Benefiting from the fast development of Chinese economy, the research in astronomy in China has made remarkable progress in recent years. The number of astronomers has doubled in the past ten years, and the number of graduate students has grown over 1300. The current budget for astronomy research is ten times larger than that ten years ago. The research covers all fields in astronomy, from galaxies to the Sun. The recent progress in both the instruments, such as the Guo Shoujing's telescope, a Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), and the theoretical research will be briefly presented. The ongoing and future projects on the space- and ground-based facilities will be described, including the Five Hundred Meter Aperture Spherical Radio Telescope (FAST), “Chang E” (Lunar mission) project, Hard X-ray Modulate Telescope (HXMT), DArk Matter Particle Explorer (DAMPE), Deep Space Solar Observatory (DSO), Chinese Antarctic Observatory (CAO), 65m steerable radio telescope, Chinese Spectral Radioheliogaph (CSRH) etc.
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25

Pereira, Ana Carolina Costa, and Bernadete Barbosa Morey. "Revisitando a lei dos cossenos para triângulos esféricos: um aporte histórico do século XV." História da Ciência e Ensino: construindo interfaces. ISSN 2178-2911 15 (May 5, 2017): 81. http://dx.doi.org/10.23925/2178-2911.2017v15p81-95.

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ResumoA Trigonometria, ramo da Matemática, percorreu um longo caminho até se consolidar como ciência independente da Astronomia. Dentre as obras que contribuíram para a história da Trigonometria Plana e Esférica está De Triangulis Omnimodis Libri Quinque de Regiomontanus, trabalho que recebeu destaque no século XVI por sua organização sistemática. Nesse artigo discutiremos a lei dos cossenos em relação aos lados de um triângulo esférico exposto nessa obra, apresentando os conceitos preliminares, o enunciado e a demonstração. Acreditamos que conhecer as origens dos conteúdos estudados por meio de fontes históricas pode possibilitar uma maior compreensão da matemática e de sua aplicação no mundo moderno. Palavras-chave: Lei dos Cossenos; Trigonometria; Regiomontanus; De Triangulis Omnimodis Libri Quinque.AbstractTrigonometry, branch of mathematics, has come a long way to be consolidated as an independent science of Astronomy. Among the compositions that contributed to the history of Flat and Spherical Trigonometry, De triangulis Omnimodis Libri Quinqueof the Regiomontanus,work that was highlighted in the sixteenth century by its systematic organization. This article will discuss the law of cosines regarding to the sides of a spherical triangle exposed in this work, showing the previous concepts, statement and demonstration. We believe that, knowing the origins of the contents studied through historical sources can enable greater understanding of mathematics and its application in the modern world.Keywords: Law of cosines; Trigonometry; Regiomontanus; De triangulis Omnimodis Libri Quinque.
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PATIL, K. D., and U. S. THOOL. "SPHERICAL AND NON-SPHERICAL GRAVITATIONAL COLLAPSE IN MONOPOLE-ANTI-DE SITTER–VAIDYA SPACE–TIME." International Journal of Modern Physics D 15, no. 11 (November 2006): 1977–84. http://dx.doi.org/10.1142/s0218271806009236.

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In the present work, we investigate the influence of the monopole field on the occurrence of the space–time singularities in the gravitational collapse of anti-de Sitter–Vaidya space–time. It has been found that the spherically symmetric monopole-anti-de Sitter–Vaidya space–time contradicts the CCH, whereas the non-spherical collapse respects it.
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Lee, Tai C., and Huan J. Keh. "Osmophoresis of a spherical vesicle in a spherical cavity." European Journal of Mechanics - B/Fluids 46 (July 2014): 28–36. http://dx.doi.org/10.1016/j.euromechflu.2014.02.007.

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28

Bauer, Adam Michael, Alejandro Cárdenas-Avendaño, Charles F. Gammie, and Nicolás Yunes. "Spherical Accretion in Alternative Theories of Gravity." Astrophysical Journal 925, no. 2 (January 31, 2022): 119. http://dx.doi.org/10.3847/1538-4357/ac3a03.

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Abstract The groundbreaking image of the black hole at the center of the M87 galaxy has raised questions at the intersection of observational astronomy and black hole physics. How well can the radius of a black hole shadow be measured, and can this measurement be used to distinguish general relativity from other theories of gravity? We explore these questions using a simple spherical flow model in general relativity, scalar Gauss–Bonnet gravity, and the Rezzolla and Zhidenko parameterized metric. We assume an optically thin plasma with power-law emissivity in radius. Along the way we present a generalized Bondi flow, as well as a piecewise analytic model for the brightness profile of a cold inflow. We use the second moment of a synthetic image as a proxy for EHT observables and compute the ratio of the second moment to the radius of the black hole shadow. We show that corrections to this ratio from modifications to general relativity are subdominant compared to corrections to the critical impact parameter, and we argue that this is generally true. In our simplified model the astrophysical parameter uncertainty dominates the gravity theory parameter uncertainty, underlining the importance of understanding the accretion model if EHT is to be used to successfully test theories of gravity.
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Zakharov, V. V., S. L. Ivanovski, J. F. Crifo, V. Della Corte, A. Rotundi, and M. Fulle. "Asymptotics for spherical particle motion in a spherically expanding flow." Icarus 312 (September 2018): 121–27. http://dx.doi.org/10.1016/j.icarus.2018.04.030.

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30

Gingerich, Owen. "Book Review: Euclid on Spherical Astronomy: Euclid's Phaenomena: A Translation and Study of a Hellenistic Treatise in Sphaerical Astronomy." Journal for the History of Astronomy 34, no. 2 (May 2003): 240. http://dx.doi.org/10.1177/002182860303400212.

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BOCHICCHIO, IVANA, MAURO FRANCAVIGLIA, and ETTORE LASERRA. "A REVIEW ON THE GEOMETRIC FORMULATION OF TOLMAN–BONDI EQUATIONS IN GENERAL RELATIVITY." International Journal of Geometric Methods in Modern Physics 06, no. 04 (June 2009): 595–617. http://dx.doi.org/10.1142/s0219887809003709.

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This work is focused on spherically symmetric space-times. More precisely, geometric and structural properties of spatially spherical shells of a dust universe are analyzed in detail considering recent results of our research. Moreover, exact solutions, obtained for constant Ricci principal curvatures, are inferred and qualitatively analyzed through suitable classic analogies.
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Nan, R., B. Peng, Y. Qiu, L. Zhu, Y. Su, and W. Zhu. "The Development of the FAST Project in China." Symposium - International Astronomical Union 199 (2002): 494–97. http://dx.doi.org/10.1017/s0074180900169657.

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Acting as a pilot of the Square Kilometer Array (SKA), the Five hundred meter Aperture Spherical Telescope (FAST) has been proposed for construction in the unique karst area of southwest China. FAST is of Arecibo-type with rather a number of innovations, among which the active main spherical reflector shows fascinating. Furthermore, the feed cabin is supported and moved by cables controlled by computer, which avoids a heavy and expensive focal pointing system. With the effective aperture of 300 m, a large sky coverage, and a broad bandwidth (200 to 2000 MHz), possible capability up to 5 ∼8 GHz, FAST will be the world's largest single dish and perform markedly role in radio astronomy.
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Zhang, Jiang Shui, Di Li, and Jun Zhi Wang. "Expectations of maser studies with FAST." Proceedings of the International Astronomical Union 8, S287 (January 2012): 350–53. http://dx.doi.org/10.1017/s1743921312007296.

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AbstractThe Five-hundred-meter Aperture Spherical radio Telescope (FAST) is being built by the Chinese and will be the largest single dish radio telescope in the world. FAST, with much increase in sensitivity, will give astronomers good opportunities to answer many fundamental questions in astronomy. Here we give a brief introduction of FAST and its enormous potential for studying Galactic and extragalactic masers.
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Mirtadjieva, K. T., and S. N. Nuritdinov. "Comparison of Instabilities of Annular Perturbations on the Background of Pulsating 2D and 3D Self-Gravitating Models." Астрономический журнал 100, no. 5 (May 1, 2023): 461–71. http://dx.doi.org/10.31857/s0004629923050079.

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The problem of gravitational instability of the observed annular (ring-like) structural perturbation modes on the background of a nonlinearly pulsating spherical model based on the well-known equilibrium Camm ball is studied. Nonstationary analogues of dispersion relations for the perturbation modes under consideration within this model are obtained. Critical diagrams of the initial virial ratio versus the model rotation parameter are constructed for each case. A comparative analysis of the increments of gravitational instability of annular perturbation modes on the background of spherical and disk-shaped nonlinearly pulsating models is also performed. An analysis of the results shows that the annular perturbation modes are predominantly more unstable in a nonstationary disk than in a spherical nonequilibrium model, regardless of the rotation parameters and the initial virial ratio of the systems. The article is partly based on a report presented at the conference “Modern Stellar Astronomy-2022” held at the Caucasian Mountain Observatory of the Sternberg Astronomical Institute of Lomonosov Moscow State University, November 8–10, 2022.
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35

Dunn, Corina, Trevor A. Bowen, Alfred Mallet, Samuel T. Badman, and Stuart D. Bale. "Effect of Spherical Polarization on the Magnetic Spectrum of the Solar Wind." Astrophysical Journal 958, no. 1 (November 1, 2023): 88. http://dx.doi.org/10.3847/1538-4357/ad03ef.

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Abstract Magnetic fluctuations in the solar wind are often observed to maintain constant magnitude of the magnetic field in a manner consistent with spherically polarized large-amplitude Alfvén waves. We investigate the effect of spherical polarization on the magnetic spectral index through a statistical survey of magnetic fluctuations observed by Parker Solar Probe between 20 R ⊙ and 200 R ⊙. We find that deviations from spherical polarization, i.e., changes in ∣ B ∣ (compressive fluctuations) and one-dimensional discontinuities, have a dramatic effect on the scaling behavior of the turbulent fluctuations. We show that shallow k −3/2 spectra are only observed for three-dimensional structures of constant magnetic field strength, which we identify as large-amplitude Alfvén waves. The presence of compressive fluctuations coincides with a steepening of the spectrum up to k −5/3. Steeper power-law scalings approaching k −2 are observed when the fluctuations are dominated by discontinuities. Near-Sun fluctuations are found to be the most spherically polarized, suggesting that this spherical state is fundamental to the generation of the solar wind. With increasing distance from the Sun, fluctuations are found to become less three-dimensional and more compressive, which may indicate the breakdown of the Alfvénic equilibrium state.
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36

Werneck, Leonardo R., Zachariah B. Etienne, Elcio Abdalla, Bertha Cuadros-Melgar, and CE Pellicer. "NRPyCritCol & SFcollapse1D: an open-source, user-friendly toolkit to study critical phenomena." Classical and Quantum Gravity 38, no. 24 (November 25, 2021): 245005. http://dx.doi.org/10.1088/1361-6382/ac33bf.

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Abstract We present a new open-source, user-friendly toolkit of two codes—SFcollapse1D and NRPyCritCol—to study critical phenomena in the context of gravitational collapse. SFcollapse1D is a C/C++ tool designed to solve the problem of gravitational collapse of massless, spherically symmetric scalar fields with the ADM formalism in spherical-like coordinates. NRPyCritCol is a collection of Python modules that leverage the NRPy+ infrastructure to generate a highly optimized C-code for evolving massless scalar fields within a covariant BSSN formalism. The toolkit was developed with user-friendliness and code efficiency in mind, enabling the exploration of critical phenomena with consumer-grade computers. We present a study of critical phenomena from the collapse of massless scalar fields in spherical symmetry, using only these two codes and a laptop computer.
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37

Ahmed, S., I. Ahmad, and K. Nawaz. "Stability of anisotropic spheres." Canadian Journal of Physics 98, no. 11 (November 2020): 1039–45. http://dx.doi.org/10.1139/cjp-2019-0620.

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This work is devoted to understanding the dynamical instability of spherically symmetric space–time in the background of Einstein-Λ gravity. For this purpose, we have considered a spherical geometric distribution and assumed that it is filled with an anisotropic fluid. To proceed with our analysis, we have calculated the corresponding field as well as the mass function. We found nonlinear behavior of physical variables. To deal with that situation, we have subjected our system to the radial perturbations. We assume that after a particular era, our structural quantities have the same time dependence parameter. After linearizing the basic expressions, we have studied the impact of the cosmological constant in the modeling of relativistic stars. It is concluded that Λ tends to slow down the rate of spherical anisotropic collapse.
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38

Knebe, Alexander, and Volkmar Wießner. "Triaxial versus Spherical Dark Matter Halo Profiles." Publications of the Astronomical Society of Australia 23, no. 3 (2006): 125–28. http://dx.doi.org/10.1071/as06013.

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AbstractWhen analyzing dark matter halos forming in cosmological n-body simulations, it is common practice to obtain the density profile utilizing spherical shells. However, it is also known that the systems under investigation are far from spherically symmetric but, rather, follow a triaxial mass distribution. In this study we present an estimator for the error introduced by spherically averaging an elliptical mass distribution. We systematically investigate the differences arising when using a triaxial density profile under the assumption of spherical symmetry. We show that the variance in the density can be as large as 50% in the outer parts of dark matter halos for extreme (but still credible) axis ratios of 0.55: 0.67: 1. The inner parts are less affected but still show a scatter at the 16% level for these prolate systems. For more moderate ellipticities, i.e. axis ratios of 0.73: 0.87: 1, the error is smaller but still as large as 10–20% depending on distance. We further provide a simple formula that allows estimation of this variance as a function of radius for arbitrary axis ratios. We conclude that highly prolate and/or oblate systems are better fit by analytical profiles that take into account the triaxial nature of cosmological objects.
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39

Tango, William J. "Spherical Astronomy Robin M. Green, Cambridge University Press, 1985, 520 pp., $44.50, paperback." Publications of the Astronomical Society of Australia 6, no. 3 (1986): 389–90. http://dx.doi.org/10.1017/s1323358000027144.

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40

Qurrota Aini, Fiki Nuafi, and Ahmad Luqman Hakim. "ANALYSIS OF SPHERICAL ASTRONOMY ALGORITHMS FOR PREDICTING THE SOLAR ECLIPSE BY W.M. SMART." Al-Hilal: Journal of Islamic Astronomy 4, no. 2 (October 31, 2022): 165–88. http://dx.doi.org/10.21580/al-hilal.2022.4.2.13293.

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A solar eclipse is an unusual natural occurrence. Muslims used the phenomenon of a solar eclipse as the season for prayer, which was only carried out during a solar eclipse from early in the phenomenon until the end. Although there is no statistically significant difference in estimating a solar eclipse, as the seasons change, a solar eclipse becomes increasingly important. Lots of alternatives can be used as a reference in the determination of a solar eclipse. Among the alternatives commonly used is the calculation of spherical astronomy. Despite its complexity, many people still use it as the foundation for calculations based on solar eclipse Pythagoras as well as the determination of the celestial coordinate system.
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41

Chellamani, P., and D. Ajay. "Spherical Fuzzy Labelling Graphs." Journal of Physics: Conference Series 1964, no. 2 (July 1, 2021): 022013. http://dx.doi.org/10.1088/1742-6596/1964/2/022013.

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42

Hohmann, Manuel. "Spherical harmonic d-tensors." International Journal of Geometric Methods in Modern Physics 16, supp02 (November 2019): 1941002. http://dx.doi.org/10.1142/s0219887819410020.

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Tensor harmonics are a useful mathematical tool for finding solutions to differential equations which transform under a particular representation of the rotation group [Formula: see text]. The aim of this work is to make use of this tool also in the setting of Finsler geometry, or more general geometries on the tangent bundle, where the objects of relevance are d-tensors on the tangent bundle, or tensors in a pullback bundle, instead of ordinary tensors. For this purpose, we construct a set of d-tensor harmonics for spherical symmetry and show how these can be used for calculations in Finsler geometry.
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43

Novopashin, S. A., and S. Z. Sakhapov. "Stability of spherical striations." Technical Physics 55, no. 7 (July 2010): 1066–67. http://dx.doi.org/10.1134/s106378421007025x.

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44

Harris, Margaret. "Consider a spherical cow." Physics World 25, no. 11 (November 2012): 68. http://dx.doi.org/10.1088/2058-7058/25/11/52.

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45

Brown, J. David. "BSSN in spherical symmetry." Classical and Quantum Gravity 25, no. 20 (September 25, 2008): 205004. http://dx.doi.org/10.1088/0264-9381/25/20/205004.

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46

Aliev, A. N., and Y. Nutku. "Impulsive spherical gravitational waves." Classical and Quantum Gravity 18, no. 5 (February 16, 2001): 891–906. http://dx.doi.org/10.1088/0264-9381/18/5/308.

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47

Saslow, W. M. "Consider a spherical battery..." American Journal of Physics 62, no. 6 (June 1994): 495–501. http://dx.doi.org/10.1119/1.17743.

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48

Smetana, Carole, David Alexander, Scott Robertson, Kim Vilkaitis, and Bob Walch. "A spherical electrostatic orrery." American Journal of Physics 64, no. 11 (November 1996): 1356–61. http://dx.doi.org/10.1119/1.18369.

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49

Burcev, P. "Nonclosed spherical gravitational sources." General Relativity and Gravitation 17, no. 11 (November 1985): 1069–79. http://dx.doi.org/10.1007/bf00774209.

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50

Herntier, Trevor, Koffi Ihou, Anthony Smith, Anand Rangarajan, and Adrian Peter. "Spherical Minimum Description Length." Entropy 20, no. 8 (August 3, 2018): 575. http://dx.doi.org/10.3390/e20080575.

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We consider the problem of model selection using the Minimum Description Length (MDL) criterion for distributions with parameters on the hypersphere. Model selection algorithms aim to find a compromise between goodness of fit and model complexity. Variables often considered for complexity penalties involve number of parameters, sample size and shape of the parameter space, with the penalty term often referred to as stochastic complexity. Current model selection criteria either ignore the shape of the parameter space or incorrectly penalize the complexity of the model, largely because typical Laplace approximation techniques yield inaccurate results for curved spaces. We demonstrate how the use of a constrained Laplace approximation on the hypersphere yields a novel complexity measure that more accurately reflects the geometry of these spherical parameters spaces. We refer to this modified model selection criterion as spherical MDL. As proof of concept, spherical MDL is used for bin selection in histogram density estimation, performing favorably against other model selection criteria.
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