We investigate the orbital evolution of an initially thin stellar disc around a supermassive black hole, considering various perturbative sources of gravity. By means of direct numerical N-body modelling, we first focus on the case when the disc is embedded in an extended spherically symmetric star cluster. We find that the gravitational influence of the disc triggers formation of macroscopic non- spherical substructure in the cluster which, subsequently, significantly affects the evolution of the disc itself. In another approximation, when the cluster is emu- lated by an analytic spherically symmetric potential, we further consider pertur- bative gravitational influence of a distant axisymmetric source. Using standard perturbation methods, we derive a simple semi-analytic model for such a config- uration. It turns out that the additional axisymmetric potential leads to mutual gravitational coupling of the individual orbits from the disc. Consequently, the dense parts of the disc can, for some period of time, evolve coherently. Finally, we apply some of our results to the young stellar disc which is observed in the innermost parsec of the Galactic Centre. 1

Depuis longtemps l’importance des commentaires des Sentences de Pierre Lombard pour les études en histoire de sciences n’est plus à démontrer. Œuvres des théologiens, ces textes traitent pourtant un grand nombre de sujets relevant de la philosophie naturelle. La question de l’influence céleste en est une preuve. Les commentateurs des Sentences l’abordent de deux façons. D’une part, ils parlent de l’influence céleste « normale », celle des sphères, des planètes et des étoiles étudiées dans les ouvrages astronomiques médiévaux. Nos auteurs décrivent en détail le rôle de ces corps supérieurs dans le système des causes, énumèrent et classifient les effets qu’ils produisent, indiquent les limites de leur pouvoir. Tout en se démarquant des astrologues, ils affirment également que les astres sont des signes à interpréter. D’autre part, les commentateurs des Sentences veulent saisir une influence céleste « extraordinaire », celle des corps supérieurs dont l’existence est postulée par les théologiens. Ils cherchent à savoir si le ciel des empyrées, l’ultime sphère de l’univers dans laquelle demeureront à la fin des temps les bienheureux, agit sur les corps terrestres. Ils s’efforcent de comprendre si, après le Jugement dernier, les planètes et les étoiles dont le mouvement cessera et dont la lumière augmentera produiront toujours des phénomènes dans le monde d’ici-bas. Notre étude poursuit un objectif double : d’abord, analyser les deux notions, celle de l’influence des cieux astronomiques et celle de l’influence des cieux théologiques, ensuite, comprendre comment elles s’articulent. Le problème de la causalité des corps supérieurs « hors normes » est-il résolu conformément à la conception de la causalité céleste « ordinaire » d’une période donnée ? Ou, inversement, cette théorie est-elle capable d’évoluer pour inclure les cas limites de l’empyrée et des cieux post-apocalyptiques ? À travers ces interrogations, nous aborderons le complexe sujet des rapports entre la théologie et la physique, entre la foi et la science. / The importance of the Commentaries on the Sentences of Peter Lombard for the history of science has been well-established for a long time. Although they were written by theologians, those texts deal with many topics coming under natural philosophy. The question of celestial influence is a good proof. The Sentences commentators address it in two ways. On the one hand, they deal with the « normal » influence, that of the spheres, planets and stars which are studied in the medieval astronomical writings. Our authors describe with scrutiny the role of the celestial bodies within the system of causes, they list and classify the effects which they produced, show the limit of their power. While distancing themselves from the astrologers, they also assert those celestial bodies are signs to be interpreted. On the other hand, the Sentences commentators want to grasp an « extraordinary » celestial influence, that of some celestial bodies, whose existence is postulated by the theologians. They seek to know if the Empyrean Heaven, the last sphere of the universe where the Blessed will live, act on terrestrial bodies. They strive to understand if, after the Last Judgement, the stars and the planets, whose motion will cease and whose light will grow, will still produce phenomena on our inferior world. Our study pursues a double goal: first, it aims to analyze the two notions, that of the influence of the astronomical heavens and that of the influence of the theological heavens; then, it aims to understand how these two notions are articulated. Is the problem of the causality of « abnormal » superior bodies solved according to the conception of the « ordinary » celestial causality at a given period? Or conversely is this theory able to evolve so that it may include the borderline cases of the Empyrean Heaven and the Post-Apocalyptic heavens? This questioning will enable us to tackle the complex issue of the relationship between theology and physics, between faith and science.

L'ensemble des travaux menés au cours de cette thèse concerne l'étude de la résonance co-orbitale. Ce domaine de trajectoires particulières, où un astéroïde et une planète gravitent autour du Soleil avec la même période de révolution, possède une dynamique très riche liée aux célèbres configurations équilatérales de Lagrange, L4 et L5, ainsi qu'aux configurations alignées de Euler, L1, L2 et L3. Un exemple majeur dans le système solaire est donné par les astéroïdes « troyens » qui accompagnent Jupiter au voisinage des équilibres L4 et L5. Une deuxième configuration étonnante est donnée par les satellites Janus et Épiméthée qui gravitent autour de la planète Saturne ; suite à la forme décrite par la trajectoire d’un des satellites dans un repère tournant avec l’autre, la dynamique résultante est appelée « fer-à-cheval ». Un nouveau type de dynamique a été récemment misen évidence dans le contexte de la résonance coorbitale : les « quasi-satellites ». Il s’agit de configurations remarquables où, dans un repère tournant avec la planète, la trajectoire de l’astéroïde correspond à celle d’un satellite rétrograde. Des astéroïdes accompagnant les planètes Venus, Jupiter et la Terre ont notamment été observés dans ces configurations. La dynamique des quasi-satellites possède un grand intérêt, pas seulement parce qu’elle relie les différents domaines de la résonance co-orbitale (voir les travaux de Namouni, 1999) mais aussi parce qu’elle semble faire le pont entre les notions de satellisation et celles de trajectoires héliocentriques. Cependant, bien que le terme « quasi-satellite" soit devenu dominant dans la communauté de mécanique céleste, certains auteurs utilisent plutôt la terminologie « satellite rétrograde » révélant ainsi une ambiguïté sur la définition de ces trajectoires. Les récentes découvertes autour des exo-planètes ont motivé le développement de travaux concernant la résonance co-orbitale dans le problème des trois corps planétaire. Dans ce contexte Giuppone et al. (2010) ont mis en évidence (par une méthode numérique) les quasisatellites ainsi que des nouvelles familles de configurations remarquables : les orbites « anti-Lagrange ». La troisième partie de thèse présente alors une méthode analytique pour l'étude planétaire, permettant de révéler analytiquement les orbites anti-Lagrange ainsi qu'une esquisse d'étude des quasisatellites en adaptant à ce contexte plus général la méthode présentée dans la seconde partie. Pour ces raisons, la première partie de cette thèse a consisté à clarifier la définition de ces orbites en revisitant le cas circulaire-plan (trajectoires coplanaires avec la planète qui gravite sur une orbite circulaire) dans le cadre du problème moyen. Dans la deuxième partie de cette thèse, nous avons développé une méthode analytique apte à explorer le domaine des quasi-satellites dans le cadre du problème moyen. Nous avons réalisé cette exploration dans le cas circulaire-plan et proposé une extension aux cas excentrique-plan et circulaire-spatial. / This work of thesis focuses on the study of the coorbital resonance. This domain of particular trajectories, where an asteroid and a planet gravitate around the Sun with the same period possesses a very rich dynamics connected to the famous Lagrange’s equilateral configurations L4 and L5, as well as to the Eulerian’s configurations L1, L2 and L3. A major example in the solar system is given by the “Trojan” asteroids harboured by Jupiter in the neighborhood of L4 and L5. A second astonishing configuration is given by the system Saturn-Janus-Epimetheus; this peculiar dynamics is known as “horseshoe”. Recently, a new type of dynamics has been highlighted in the context of co-orbital resonance: the quasi-satellites. They correspond to remarkable configurations : in the rotating frame with the planet, the trajectory of the asteroid seems the one of a retrograde satellite. Some asteroids harboured by Venus, Jupiter and the Earth have been observed in this kind of configuration. The quasi-satellite dynamics possesses great interest not only because it connects the different domains of the co-orbital resonance (see works of Namouni, 1999), but also because it seems to bridge the gap between satellization and heliocentric trajectories. However, despite the term quasi-satellite has become dominant in the celestial mechanics community, some authors rather use the term “retrograde satellite”. This reveals an ambiguity on the definition of these trajectories. For these reasons, the first part of this thesis consisted in clarifying the definition of these orbits by revisiting the planar-circular case (planet on circular motion) in the framework of the averaged problem. In the second part of this thesis, we developed an analytic method to explore the quasi-satellite domain in the averaged problem. We realized this exploration in the planar-circular case and proposed an extension to the planar-eccentric and spatial-circular cases. The recent discoveries around the exo-planets motivated some works on the co-orbital resonance in the planetary Three-Body Problem. In this context, Giuppone et al. (2010) highlighted (numerically) the quasi-satellite as well as new families of remarkable configurations: the “anti-Lagrange”. Then the third part of this thesis presents an analytical method for the planetary problem that allows to reveal the anti-Lagrange orbits as well as a sketch of study of quasi-satellite trajectories.

Le modèle de nutation de référence (MHB2000) et le repère céleste international (ICRF2) ont été établis en 2000 et en 2009 respectivement. Les observations VLBI s’étant accumulées depuis, ce sont autant de nouvelles données permettant d’affiner la nutation et de mieux caractériser l’instabilité des radiosources constituant le repère céleste. L’allongement des données disponibles révèle des défauts dans la nutation de référence comme des fluctuations dans la position des radiosources. Il importe donc de réajuster les termes de nutation, tout en évaluant l’impact de l’instabilité du repère de référence céleste sur celle-ci. Dans un premier temps, nous déterminons des corrections significatives des termes de nutation du modèle MHB2000 jusqu'à 50 micro-seconde d'arc sur la base des séries opérationnelles de l'IVS. Nous en évaluons aussi l'incertitude. Notre intérêt s’est focalisé sur la nutation libre du noyau et un terme spectralement proche, le terme annuel rétrograde. Nous tentons de caractériser leur variabilité multi-annuelle, en amplitude, phase et fréquence, malgré la corrélation qui les affecte.Dans un second temps, nous avons étudié la stabilité du repère céleste par une étude approfondie des sources susceptibles de définir ce repère. De telles sources sont sélectionnées par analyse de variance d'Allan de leurs déplacements astrométriques. Cette analyse donne la « couleur » du bruit aléatoire qui affecte leurs positions en fonction des différentes échelles de temps correspondant à 30 ans d’observations VLBI. Plus précisément, nous sélectionnons les radiosources présentant un bruit blanc. Il en résulte que sur 123 sources parmi celles choisies pour l'ICRF2 en 2009, seules 40 respectent ce critère de stabilité sur la période 1985-2016. Ce nombre est insuffisant pour construire un repère céleste stable et des compromis sont nécessaires. Enfin, la propagation des erreurs des positions des radiosources sur la nutation a été caractérisée, expliquant le bruit anormalement grands de certaines séries de nutation diffusées par l'IVS. / The reference nutation model (MHB2000) and the International Celestial Reference Frame (ICRF2) was established in 2000 and 2009 respectively. VLBI observations are being accumulated since and these are all new data to refine the nutation and better characterize the instability of radio sources constituting the celestial frame. The lengthening of the available data reveals defects in the reference wobble and fluctuations in the position of radio sources.It is important to adjust the nutation terms while assessing the impact of the instability of the celestial reference frame on it. Initially, we obtain significant corrections in terms of nutation model MHB2000 up to 50 micro-seconds of degree on the basis of IVS operational nutation time series. We also evaluate their uncertainty. Our interest is focused on the the free core nutation and a term closed in frequency, the retrograde annual term. We try to characterize the multi-annual variability, on amplitude, phase and period, despite correlation that affects both terms.Secondly, we study the stability of the celestial reference frame by a comprehensive study of the potential sources to define the frame. Such defining sources are selected by analysis using Allan variance of their astrometric displacements. This analysis gives the "color" of the random noise that affects positions based on different time scales corresponding to 30 years of VLBI observations. Specifically, we select radio sources with white noise. It follows that on 123 sources from those chosen for ICRF2 in 2009, only 40 meet this criterion of stability over the period 1985-2016. This number is too small to build a new celestial reference frame and compromises are necessary. Finally, errors propagation of radio position on nutation has been characterized, explaining the noise unusually large of some nutation time series diffused by the IVS.

Orientadores: Maximiliano Ujevic Tonino, Javier Fernando Ramos Caro, Carola Dobrigkeit Chinellato / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-20T00:26:31Z (GMT). No. of bitstreams: 1 AlarconLLacctarimay_CesarJuan_D.pdf: 2806949 bytes, checksum: 588125c56d514dbfd77030a564888461 (MD5) Previous issue date: 2012 / Resumo: Nesta tese pretendemos modelar a distribuição de matéria em um Anel estelar fino imerso no campo gravitacional de um e dois Satélites Shepherds (Satélites Pastores) usando a equação de Fokker-Planck. Em particular, estudamos a evolução de um anel fino ao redor de um monopolo central. Os coeficientes de difusão são aqui calculados e escritos em termos de um ¿potencial¿ semelhante aos usuais potencias de Rosenbluth. Neste caso, consideramos que as partículas campo obedecem uma distribuição Gaussiana. Resolvemos a equação de Fokker-Planck 1-dimensional para a função de distribuição das partículas teste que conformam o anel usando o método das diferenças finitas (versão Euler implícita). Demonstramos que o anel é uma configuração estável para uma evolução de longo tempo, tanto na ausência como na presença de shepherds. Estudamos também a variação da densidade de massa do anel para diferentes configurações. Em todos os casos é observada uma variação máxima e negativa da densidade perto da localização do shepherd devido a efeitos dinâmicos / Abstract: In this thesis we intend to model the distribution of matter in a thin stellar ring immersed in the gravitational field of one and two shepherd satellites using the Fokker-Planck equation. In particular, we study the evolution of a thin ring around a central monopole. The diffusion coefficients are calculated and written in terms of a ¿potential¿ similar to the usual Rosenbluth potentials. In this case, we consider that the particles follow a Gaussian distribution. We solve the 1-dimensional Fokker-Planck equation for the ring particles distribution function using the finite difference method (implicit Euler version). We show that the ring is a stable configuration for long time evolutions in the absence or in the presence of shepherds. We also studied the change in the mass density of the ring for different configurations. In all of the cases, it is observed a maximum negative variation of the density near the location of the shepherd due to dynamical effects / Doutorado / Física / Doutor em Ciências

Star clusters are thought to be the birthplaces of stars as well as the building blocks of galaxies. They typically consist of thousands to millions of stars bound together by self-gravity. These systems evolve on the scale of Myr to Gyr, there- fore, it is impossible for us to see any change in their global evolution even within hundreds of human lifetimes. Although the equations of motion of stars in a star cluster are simple New- tonian, it is impossible to predict precisely history of any star within them to any point in the future. Therefore, we may either compare the observations of different star clusters at different age, we may invent theoretical approaches and analytical predictions, or we must follow their evolution numerically (e.g. with direct N-body integrators) which is the main focus of my research and this thesis. First, we follow the evolution of star clusters in general while coming up with a novel method to estimate their characteristic timescale (i.e. the time of core collapse) based on global parameters. The core collapse is directly linked to the formation of hard binary stars, thus, we focus on their analysis as well. We also follow several recent observational results: (i) ALMA observations of the Serpens South star-forming region indicate that star clusters are born mass...

[pt] Dado o recente aumento da adoção de fontes renováveis de energia, é essencial reavaliar os sistemas tradicionais de energia. A intermitência pode causar diversos problemas ligados à qualidade e eficiência energética. O objetivo desta dissertação de mestrado é desenvolver uma ferramenta capaz de subsidiar modelos de previsão solar para aplicações visando a melhoria da operação em tempo real. O atual paradigma de previsão solar sub-horária consiste em usar imagens celestiais para prever a cobertura nebulosa para curtos horizontes temporais. Visando desenvolver um modelo mais exato, é necessária a utilização de componentes determinísticos, como a temperatura e o ângulo de incidência dos raios solares, em conjunto com a modelagem dos efeitos estocásticos das nuvens. Visto que o objetivo da previsão sub-minuto é permitir que se lide com variações de alta frequência, os dados devem possuir informação condizente com estas frequências. Por esse motivo foi feita a coleta de dados por exclusão. O sistema captura dados a cada 1 s e, quando detecta uma mudança suficientemente grande na potência do painel, salva essa informação, 10 s para trás até 4 s à frente da perturbação detectada. Os dados, depois de pré-processados, foram usados para treinar uma rede neural para determinar a relevância dos dados. Com cuidadosa seleção de atributos e arquitetura de rede, o modelo apresentou boa regressão com R2 maior que 0.93 para ambas variáveis testadas com horizonte de 60 s à frente. Concluindo, portanto, que os dados obtidos são relevantes para previsões de até 60 s à frente. / [en] The rising adoption of renewable energy sources means we must turn our eyes to limitations in traditional energy systems. Intermittency, if left unaddressed, may lead to several power quality and energy efficiency issues. The objective of this work is to develop a working tool to support PV energy forecast models for real-time operation applications. The current paradigm of intra-hour solar power forecasting is to use image-based approaches to predict the state of cloud composition for short time-horizons. For a more accurate model, it is also necessary to use deterministic components such as temperature and angle of incidence on the panels in addition to the stochastic effect of clouds. Since the objective of intra-minute forecasting is to address high-frequency intermittency, data must provide information on and surrounding these events. For that purpose, acquisition by exception was chosen as the guiding principle. The system performs power measurements at 1 Hz frequency and whenever it detects variations over a certain threshold, it saves the data 10 s before and 4 s after the detection point. After post-processing, this data was fed into a multilayer perceptron neural network to determine its relevance to the forecasting problem. With a thorough selection of attributes and network structures, the results show very low error with a normalized good fitting with R2 greater than 0.93 for both input variables tested with a time horizon of 60 s. In conclusion, the data provided by the acquisition system yielded relevant information for forecasts up to 60 s ahead.

Lorsqu’un fort effet de marée entre Saturne et ses satellites de glace a été révélé il y a plusieurs années, le système a été sujet à des nombreux questionnements concernant sa formation et son évolution. Une implication importante de ces résultats est que les satellites sont plus jeunes que la planète et ont subi d’importantes modifications orbitales durant leurs évolutions, rendant possible plusieurs traversées en résonance. Dans cette thèse, nous cherchons à vérifier le scénario selon lequel Titan serait à l’origine de l’orbite actuelle de Japet. Si Titan a fortement migré lui aussi, alors il a dû traverser la résonance 5:1 avec Japet. Or, l’orbite de Japet admet deux éléments orbitaux dont les origines restent à être déterminées clairement : d’une part une inclinaison de 8 degrés par rapport à son plan de Laplace et d’autre part, une orbite excentrique d’environ 0,03. En plaçant initialement Japet sur une orbite circulaire et coplanaire avec le plan de Laplace, de nombreuses simulations numériques de la traversée en résonance, utilisant un code N-Corps ainsi qu’un modèle semi-analytique, ont été réalisées. L’analyse des simulations montre que les résultats sont très dépendants de la dissipation interne de la planète, paramétrée par le facteur de qualité Q. Pour des valeurs au-delà d’environ 2000, on obtient en majorité l’éjection de Japet lorsque Titan traverse la résonance. Pour des vitesses de migration élevées (Q en dessous de 100 environ) Japet est très peu perturbé par Titan. Le nombre d’éjections croît avec la valeur de Q et pour des valeurs entre 100 et 2000 la plupart des simulations montrent une capture en résonance, une évolution chaotique de l’excentricité et de l’inclinaison, puis une libération avec des éléments orbitaux perturbés. La valeur des excentricités après la résonance varie entre 0 et 0.15 et l’inclinaison peut croître jusqu’à 11 degrés. Sur 800 simulations effectuées avec le code N-Corps, 2 montrent une sortie de résonance de Japet avec des éléments en accord avec ceux observés actuellement. De plus, en comptant celles venant du modèle semi-analytique, plus d’une vingtaine montrent une inclinaison libre ayant dépassé 4 degrés. Ces simulations numériques nous ont permis de contraindre le facteur de dissipation de la planète à la fréquence de Titan. C’est pour une valeur de Q entre 100 et 2000 que les simulations de traversée en résonance rendent compte au mieux de l’orbite actuelle de Japet, rendant ainsi plausible le scénario d’un récente perturbation de Japet par Titan lors de la traversée de la résonance 5:1. / When a strong tidal interaction between Saturn and its icy satellites was revealed a few years ago, the formation of the system and its evolution were subject to questioning. These results imply that the satellites are younger than the planet and underwent important orbital modifications during their evolution, making possible many mean motion resonance crossings between satellites. In this thesis, we assume that Titan migration is also important, increasing its semi-major axis in time, and crossing a 5:1 resonance with Iapetus. Today, Iapetus’ orbital plane is tilted with respect to a natural equilibrium plane called the Laplace plane, on which a satellite should have naturally been formed. But, among having non-null eccentricity, Iapetus’ orbit stays on a constant 8 degree tilt with respect to this equilibrium plane. We are therefore assessing the possibility for Titan to be responsible for Iapetus’ orbit.Starting with Iapetus on a circular orbit with its orbital plane co-planar with the Laplace plane, we have used a N-Body code and a semi-analytic model to perform numerous numerical simulations.The analysis of the simulations show that the results are very dependent on the quality factor, Q. For values greater than 2000, Iapetus is more likely to get ejected during the crossing of the resonance, whereas setting a fast migration for Titan (Q below 100) avoids any strong perturbation of Iapetus’ orbit. The ejection likelihood increases with Q and for values between 100 and 2000, many simulations show a resonance capture, followed by a chaotic evolution of the eccentricity and the inclination, then a release with perturbed orbital elements. The range of values for post-resonance eccentricities are between 0 and 0.15 while the tilt can grow up to 11 degrees. Out of 800 simulations done with the N-Body code, 2 show elements compatible with Iapetus’ actual orbit. In addition, more than twenty simulations show a tilt having raised over 4 degrees if we count the simulation done with the semi-analytic model.These numerical simulations allowed us to constrain the tidal dissipation of the planet at Titan’s frequency. Some simulations performed with Q between 100 and 2000 account for the orbit of Iapetus we observe today, making plausible the scenario where the resonance with Titan was the source of Iapetus’ perturbed orbit.

The research work presents the carried out investigations on the effect of the celestial bodies on the gravity field elements and the analysis was made on the Moon’s and Sun’s effect on the geodetic measurements. The results of the research are advised to be implemented for the assessment of the effect of the celestial bodies regarding the geodetic, measurements as well as when selecting the surfaces of the Earth and geoid and the system of gravity. The dissertation consists of introduction, four chapters and the summation of the results. The introduction depicts the topicality of the chosen research, determining the relevance of the investigated issue. There are described the objective of the work as well as the tasks, there is revealed the scientific novelty of the work ant etc. Chapter one deals with the review of the scientific literature. The chapter also presents the analysis of the available methods of the assessment of the Earth’s tides and their accuracies. The scientific literature was analysed extensively in terms of the effect of the celestial bodies on the Earth’s gravity field and on the issues of the geodetic measurements. The problems were indicated concerning the assessment of the effect of the celestial bodies and the tasks were specified for the research work to be investigated. Chapter 2 deals with the theoretical research. The author presents the analysis of the effect of the members of the series of the tide potential caused by the celestial bodies on... [to full text] / Disertacijoje pateikti dangaus kūnų įtakos sunkio lauko elementams tyrimai ir nagrinėjamas Mėnulio ir Saulės poveikis geodeziniams matavimams. Pagrindinis disertacijos tikslas – ištirti ir įvertinti dangaus kūnų poveikį sunkio lauko elementams ir patobulinti dangaus kūnų poveikio geodeziniams matavimams įvertinimo metodikas. Atlikto darbo rezultatus galima panaudoti vertinant dangaus kūnų poveikį geodeziniams, gravimetriniams ir geodezinės astronomijos matavimams, taip pat pasirenkant Žemės ir geoido paviršius bei sunkio sistemą, dangaus kūnų poveikio įvertinimo atžvilgiu. Disertaciją sudaro įvadas, keturi skyriai ir rezultatų apibendrinimas. Įvadiniame skyriuje pagrindžiama tiriamoji problema, apibrėžiamas problemos aktualumas, formuluojamas darbo tikslas bei uždaviniai, aprašomas mokslinis darbo naujumas, pateikiami ginamieji disertacijos teiginiai pristatomos autoriaus publikacijos ir pranešimai konferencijose, aprašoma disertacijos struktūra. Pirmasis skyrius skirtas literatūros analizei. Jame nagrinėjami esami Žemės potvynių įvertinimo metodai ir jų tikslumas. Išanalizuota mokslinė literatūra dangaus kūnų poveikio Žemės sunkio laukui ir geodeziniams matavimams klausimais. Identifikuotos problemos dangaus kūnų poveikio vertinime ir suformuluoti uždaviniai, kuriuos disertaciniame darbe tikslinga išspręsti. Antrajame disertacijos skyriuje pateiktas teorinis tyrimas. Nagrinėjamas dangaus kūno lemiamo potvynio potencialo eilutės narių poveikis sunkio lauko elementams:... [toliau žr. visą tekstą]

Sammanfattning De flesta barn fängslas och visar intresse för temat rymden och finner vanligtvis att det är ett mycket intressant ämne. Fokusgruppen har varit elever i årskurs 4-6 och efter några större bortfall var det slutligen elever ifrån 8 klasser som deltog, totalt 94 elever. Eleverna fick svara på en enkät där eleverna i både text och bild bland annat fick förklara hur de trodde att objekten i sol–jord–månsystemet samverkade och rörde sig i förhållande till varandra, vad de placerade i centrum för detta system, hur de såg på orsaken till årstider samt varför vi har dag och natt. De två pedagogerna som undervisade klasserna fick svara på några frågor om hur de såg på undervisningen om astronomi, om den undervisningsmetod de använde sig av och på elevernas lärande och förståelse för ämnet astronomi.    I denna undersökning kunde samma typer av missuppfattningar ses hos dessa elever, som de missuppfattningar som har dykt upp i en rad olika undersökningar som genomförts tidigare år med andra barn ifrån olika länder. Några av de missuppfattningar som fanns hos eleverna i denna undersökning var bland annat att jorden var mittpunkten, något som en femtedel av eleverna visade. Att sol och måne låg i samma omloppsbana runt jorden, årstiderna orsakas av att avståndet till solen förändras och att dag/natt beror på jordens omloppsbana runt solen var några andra missuppfattningar som rådde bland eleverna. Användandet av konkret material och 3D-modeller i undervisningen om rymden tycks vara en viktig del för elevernas förståelse av området.   Nyckelord: undervisning om rymden – astronomiska missförstånd – årstider – dag/natt – omloppsbanor i sol–jord–månsystemet / Abstract Most children find astronomy an interesting subject and usually show an interest during lessons about the subject. The focus group in this paper is Swedish students in school year 4-6. In total there were 94 students from eight classes who answered the survey with simple drawings and explanations about for example how they thought the objects Sun–Earth–Moon orbit each other, which object they placed as the center in this system, what causes season and the reason behind day and night. Two teachers whom educate the students answered some questions about their teaching method, their thoughts about the subject in question and the students learning and understanding of astronomy.   In the study that are presented in this paper the same types of astronomical misconceptions can be seen amongst these students, that has been shown in similar studies of children all over the world. 20 % of the children in this study showed an earth centered Sun–Earth–Moon system. Other misconceptions that were shown was: the sun and the moon shares the same orbit around the earth, that the seasons are caused by the distance to the sun changing and that day and night happens because the earth orbits the sun. The use of concrete material and 3D-models in the education seemed to be important for the students understanding of the subject.   Keywords: Astronomy education – astronomy misconceptions – seasons – day/night – Celestial Motion in the Sun–Earth–Moon system