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Une Histoire De L'astronomie D'une Grande Importance Pour Comprendre Le Cadre De Sa Pensée

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Une Histoire De L'astronomie D'une Grande Importance Pour Comprendre Le Cadre De Sa Pensée UNEUNE HISTOIREHISTOIRE DEDE L’ASTRONOMIEL’ASTRONOMIE la Préhistoire - l’Antiquité - le Moyen-Âge la Renaissance - l’Âge de Raison le siècle des Lumières - le XIX° siècle les XX° et XXI° siècles - iconographie GAP 47 • Olivier Sabbagh • Mars 2016 / Revision Janvier 2020 Une histoire de l’astronomie Préambule Etablir et rassembler un document intitulé « une histoire de l’astronomie » peut paraître très ambitieux et procède de nombreux choix qui, en tant que tels, sont nécessairement subjectifs. Nous sommes confrontés au premier choix qui consiste à prendre la voie de l’encyclopédie, pour tout dire, tout explorer et être totalement exhaustifs. La conséquence en serait la production d’un volume incalculable de données, d’évènements, de noms, de photos, etc. Faire le choix de cette approche serait très long et difficile, sauf au prix de produire des milliers de pages qui, ipso facto, seraient probablement illisibles et dans lesquelles le lecteur pourrait facilement se perdre, voire se lasser ou s’ennuyer. L’autre approche, celle que nous avons choisie, est celle de l’arbitraire, en faisant certains choix à priori : parler de telle ou telle découverte plutôt que d’autres, parler sommairement de la famille et/ou de la personnalité de certains astronomes, parler de certaines civilisations pour voir ce qu’elles ont apporté à la science du ciel et des étoiles et à notre compréhension progressive de l’Univers dans lequel nous nous trouvons. Comme les choix que nous avons faits sont arbitraires, ils sont nécessairement discutables puisque biaisés, en ne retenant que ce qui nous paraît le plus important et en laissant donc de côté ce qui nous semble secondaire (ou moins indispensable). Par ailleurs, nous avons été frappés par le fait que cette histoire présente clairement trois types de structure suivant les âges : 1) De la préhistoire jusqu’au Moyen-Âge ou à l’aube de la Renaissance, l’astronomie est générée et portée par des peuples, des civilisations, des croyances religieuses, des rites. Bien sûr, dans ces contextes culturels, il y a des hommes qui se sont mis en avant par leurs qualités intellectuelles et « novatrices », mais ils s’inscrivent clairement dans leur environnement socioculturel, spirituel et géographique. 2) Du milieu de la Renaissance jusqu’à la seconde guerre mondiale, on change complètement de structure. On assiste à la mise en avant d’individus isolés dont le génie, la créativité et l’inventivité prennent ostensiblement le pas sur leur environnement sociétal. Ces hommes se sont même souvent mis en opposition, en conflit (voire même parfois en danger) avec les idées établies ou les dogmes de leurs époques respectives. Ce furent, individuellement, des pionniers, des aventuriers de l’astronomie. 3) Puis, dans la deuxième moitié du XX° siècle, on revient à une astronomie de groupe. Mais pas pour les mêmes raisons que celles qui ont prévalu à la première époque. A partir des années 1950/1960, la technologie et la science en général ont fait des progrès considérables et foudroyants. On sent alors une fantastique accélération technologique. On commence à lancer des satellites dans l’espace. On envoie des hommes sur la Lune. On lance des sondes vers les planètes du système solaire. On pose des robots sur la Lune, Mars et Vénus. On met des télescopes en orbite pour s’affranchir des inconvénients de l’atmosphère terrestre, des télescopes qui « voient » non seulement dans le spectre visible mais également dans l’infrarouge, l’ultraviolet, les rayons X, les rayons gamma ou les ondes radio. Le problème est que tout cela coûte très cher et n’est plus finançable par les individus. Il y a clairement une internationalisation de l’astronomie. Il est donc nécessaire de s’appuyer sur des organisations scientifiques et/ou des états, ou encore des regroupements d’états pour construire des gigantesques télescopes (Chili, Hawaï, etc.), envoyer une sonde poser un atterrisseur sur une comète ou envisager d’envoyer des hommes sur Mars. Les individus qui étaient jadis financés par des mécènes ou souverains du XV° au XVIII° siècle ne sont plus là. Les Etats prennent le relais, au travers d’organisations structurées qui recrutent et forment des individus (astrophysiciens, informaticiens, mathématiciens, etc.) qui travaillent obligatoirement dans des équipes. Exception : Stephen Hawking ! Bonne lecture ! Une histoire de l’astronomie Olivier Sabbagh GAP 47 Mars 2016 page 1 Nabta Playa Vieille de plusieurs milliers d'années d'histoire, l’astronomie est probablement une des plus anciennes des sciences naturelles, ses origines remontant au-delà de l'Antiquité, dans les pratiques religieuses préhistoriques. L'astronomie est la science de l'observation des astres et cherche à expliquer leur origine, leurs éventuelles évolutions et aussi l'influence qu'ils ont sur la vie de tous les jours : marées, crue du Nil, canicule, etc. Cette influence se manifeste par certains phénomènes exceptionnels (les éclipses, les comètes, les étoiles filantes, etc.) qui pour certains étaient des événements majeurs dans le rythme de vie de la communauté comme les saisons et pour d'autres la possibilité de mieux faire avancer les connaissances au niveau de la compréhension de l'univers céleste. Elle ne doit pas cependant être confondue avec des disciplines très proches telles que l’archéoastronomie, la mécanique céleste qui n'en sont que des domaines particuliers. L'étymologie du terme astronomie vient du grec αστρονομία (άστρον et νόμος) ce qui signifie loi des astres. L'astronomie est peut-être la plus ancienne des sciences, comme semblent l'indiquer nombre de découvertes archéologiques datant de l'âge du bronze et du Néolithique. Certaines civilisations de ces périodes avaient déjà compris le caractère périodique des équinoxes et sans doute leur relation avec le cycle des saisons, elles savaient également reconnaître quelques dizaines de constellations. L'astronomie moderne doit son développement à celui des mathématiques depuis l'Antiquité grecque et à l'invention d'instruments d'observation à la fin du Moyen Âge. Si l'astronomie s'est pratiquée pendant plusieurs siècles parallèlement à l'astrologie, le siècle des Lumières et la redécouverte de la pensée grecque ont vu naître la distinction entre la raison et la foi, si bien que l'astrologie n'est plus pratiquée par les astronomes de nos jours. Stonehenge Certains ont même pu imaginer que des dessins et peintures rupestres pouvaient faire penser à la représentation de certaines constellations dans les Grottes de Lascaux (Dordogne) ou Blanchard (Indre), mais ces hypothèses sont invérifiables. Il semble que les premières traces évidentes d’une relation entre l’astronomie et des constructions humaines ne commencent qu’à partir du néolithique. Une histoire de l’astronomie Olivier Sabbagh GAP 47 Mars 2016 page 2 I La préhistoire L'observation du ciel à la Préhistoire Par définition, il n'existe pas d'information directe ou écrite concernant les observations du ciel au Paléolithique. Seuls de rares indices isolés permettent de les soupçonner. Selon de rares auteurs tels qu'Alexander Mashack ou Chantal Jègues-Wolkiewiez, paléo-astronome, certains objets témoigneraient de l'observation des astres, du Soleil ou de la Lune en dressant une cartographie des positions des objets célestes. Selon A. Marshack, les indentations gravées sur un os d’aigle mis au jour dans l’abri Blanchard et datant d'environ 32 000 ans correspondraient à des notations lunaires : leur nombre et leur position pourraient être mis en rapport avec les lunaisons. Selon C. Jègues-Wolkiewiez, l'ornementation spécifique des grottes du sud de la France, lorsque celle-ci correspond par exemple à des solstices, serait un autre élément significatif. Cet auteur considère même que les peintures de ces grottes pourraient être des cartographies stellaires. Pour elle, la scène du Puits de la grotte de Lascaux (environ 17 000 ans), supposerait des connaissances astronomiques : elle croit y reconnaître une représentation des Pléiades et du zodiaque. « La visualisation de la lumière solaire sur la porte d'entrée de la grotte pendant 50 minutes environ lors du coucher solaire au moment du solstice d'été, confirme cet éclairement complet de la rotonde pendant cette période solsticiale au temps de la création de l'œuvre. Éclairement permettant même un travail en pleine lumière, presque durant une heure pendant quelques jours par an au début de l'été. Mais aussi lumière de la pleine lune le matin lors du solstice d'hiver ». La signification profonde de ces cartographies est inconnue; elle pourrait être d'ordre religieux ou calendaire, marquant les grandes périodes de migration, de chasse, etc. Toutefois, cette interprétation n'a été publiée dans aucune revue à comité de lecture et est accueillie avec scepticisme par la communauté scientifique. Quoi qu'il en soit, le manque d'indices archéologiques explicites ne signifie aucunement que l'observation du ciel ne jouait aucun rôle chez les hommes préhistoriques : celle-ci est bien attestée dans les cultures des chasseurs-cueilleurs contemporaines, comme les aborigènes d'Australie. Au Néolithique, les sources se multiplient même si leur interprétation demeure délicate. La mise en œuvre de calendriers, qui témoignent de connaissances certaines de l'évolution du ciel, revêtait pour ces civilisations agraires une importance vitale. La possibilité d'anticiper les événements saisonniers ou annuels rendait la planification possible. On attachait ainsi aux causes possibles des phénomènes célestes une interprétation religieuse. L'émergence des pratiques agraires s'est peut-être accompagnée de la pratique de divers cultes ouraniens (qui se rapportent au ciel, espace dédié au sacré) et, avec cela, de l'astronomie et de l'astrologie (aussi bien d'ailleurs, de l'astrologie chaldéenne que chinoise). D'innombrables sépultures de cette époque sont orientées dans une direction du ciel particulière. Parmi les découvertes archéologiques associées à une pratique du calendrier, il y a lieu de citer les cônes d'or rituels mis au jour en France et en Allemagne méridionale, interprétés comme les couvre-chefs de prêtres d'un culte solaire, et le disque de Nebra.
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