{"id":7787,"date":"2017-06-18T19:49:24","date_gmt":"2017-06-18T19:49:24","guid":{"rendered":"https:\/\/blogs.futura-sciences.com\/feldmann\/?p=7787"},"modified":"2017-06-28T13:41:04","modified_gmt":"2017-06-28T13:41:04","slug":"a-decouverte-etoiles-doubles-mizar-alcor","status":"publish","type":"post","link":"https:\/\/blogs.futura-sciences.com\/feldmann\/2017\/06\/18\/a-decouverte-etoiles-doubles-mizar-alcor\/","title":{"rendered":"\u00c0 la d\u00e9couverte des \u00e9toiles doubles Mizar et Alcor"},"content":{"rendered":"

Dans la constellation de la Grande Ourse les \u00e9toiles doubles Mizar et Alcor n’ont cess\u00e9 de surprendre les astronomes depuis qu’ils les observent.<\/strong><\/p>\n

L\u2019une des constellations les plus c\u00e9l\u00e8bres est appel\u00e9e Grande Ourse ou Grand Chariot. Il s’agit de\u00a0la troisi\u00e8me plus grande constellation du ciel mais on a souvent tendance \u00e0 la r\u00e9duire \u00e0 ses sept \u00e9toiles les plus brillantes dont la forme \u00e9voque une casserole : les \u00e9toiles du manche sont Alka\u00efd, Mizar et Alioth, celles du r\u00e9cipient sont Megrez, Phecda, Merak et Dubhe. Cette constellation est circumpolaire comme celle de Cassiop\u00e9e<\/a>, ce qui signifie qu\u2019elle ne se couche jamais pour un observateur situ\u00e9 aux latitudes de la France.<\/p>\n

\"\"<\/a><\/p>\n

<\/span>Nous allons aujourd’hui nous int\u00e9resser \u00e0 l’\u00e9toile Mizar qui poss\u00e8de un compagnon tr\u00e8s proche, Alcor.\u00a0La l\u00e9gende veut que tout archer capable de distinguer les deux \u00e9toiles \u00e0 l\u2019\u0153il nu \u00e9tait admis dans l\u2019arm\u00e9e de Gengis Khan, le terrible chef mongol.<\/p>\n

Mizar (Zeta Ursae Majoris<\/em>) est une \u00e9toile de magnitude 2,27 ; Alcor (0 Ursae Majoris<\/em>) est un peu plus faible (magnitude 3,99) et en est distante de 11,5 minutes d’arc, ce qui repr\u00e9sente environ le tiers du diam\u00e8tre apparent de la Pleine Lune<\/a>. Ce couple d’\u00e9toiles se trouve \u00e0 un peu moins de 80 ann\u00e9es-lumi\u00e8re de la Terre.<\/p>\n

Jusqu’\u00e0 l’\u00e9poque de Galil\u00e9e<\/a> les hommes ne voyaient l\u00e0 que deux \u00e9toiles tr\u00e8s proches, mais l’invention de la lunette astronomique<\/a> et ses perfectionnements allaient peu \u00e0 peu changer notre vision de ce couple c\u00e9leste.<\/p>\n

Vers 1650 l’astronome italien Giovanni Battista Riccioli constate que Mizar est elle-m\u00eame une \u00e9toile double : Mizar B (magnitude 4) tourne autour de Mizar A. Puis en 1889 c’est l’astronome am\u00e9ricain\u00a0Edward Charles Pickering qui parvient \u00e0 d\u00e9doubler Mizar A et en 1908 on d\u00e9couvre que Mizar B est \u00e9galement une double ! Nous en sommes donc \u00e0 un syst\u00e8me quintuple : Mizar A (2 \u00e9toiles), Mizar B (2 \u00e9toiles) et Alcor. Vous suivez toujours ?<\/p>\n

Dernier rebondissement en 2009, quand \u00c9ric Mamajek (University of Rochester<\/em><\/a>) d\u00e9couvre avec ses coll\u00e8gues que Alcor est \u00e9galement un syst\u00e8me binaire, portant \u00e0 six le nombre de composantes du syst\u00e8me Mizar-Alcor, en attendant peut-\u00eatre de nouvelles d\u00e9couvertes…<\/p>\n","protected":false},"excerpt":{"rendered":"

Dans la constellation de la Grande Ourse les \u00e9toiles doubles Mizar et Alcor n’ont cess\u00e9 de surprendre les astronomes depuis qu’ils les observent. L\u2019une des constellations les plus c\u00e9l\u00e8bres est appel\u00e9e Grande Ourse ou Grand Chariot. Il s’agit de\u00a0la troisi\u00e8me plus grande constellation du ciel mais on a souvent tendance \u00e0 la r\u00e9duire \u00e0 ses … Continuer la lecture de \u00c0 la d\u00e9couverte des \u00e9toiles doubles Mizar et Alcor<\/span> →<\/span><\/a><\/p>\n","protected":false},"author":8,"featured_media":7788,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","_links_to":"","_links_to_target":""},"categories":[84],"tags":[2199,2197,456,2200,2201,2195,2125,2196,2198],"class_list":["post-7787","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-ciel-etoile","tag-80-ursae-majoris","tag-alcor","tag-constellation-de-la-grande-ourse","tag-edward-charles-pickering","tag-eric-mamajek","tag-etoile-double","tag-giovanni-battista-riccioli","tag-mizar","tag-zeta-ursae-majoris"],"yoast_head":"\n\u00c0 la d\u00e9couverte des \u00e9toiles doubles Mizar et Alcor<\/title>\n<meta name=\"description\" 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