{"id":2903,"date":"2026-09-07T00:12:41","date_gmt":"2026-09-06T23:12:41","guid":{"rendered":"https:\/\/www.laurensoff.com\/wordpress\/?p=2903"},"modified":"2026-09-07T00:12:41","modified_gmt":"2026-09-06T23:12:41","slug":"ca-represente-quoi-68-annees-lumiere","status":"publish","type":"post","link":"https:\/\/www.laurensoff.com\/wordpress\/ca-represente-quoi-68-annees-lumiere\/","title":{"rendered":"\u00e7a repr\u00e9sente quoi 68 ann\u00e9es-lumi\u00e8re ?"},"content":{"rendered":"<p data-path-to-node=\"0\">Une distance de <b data-path-to-node=\"0\" data-index-in-node=\"16\">68 ann\u00e9es-lumi\u00e8re<\/b> correspond au trajet parcouru par la lumi\u00e8re dans le vide pendant 68 ans.<\/p>\n<p data-path-to-node=\"1\">Voici quelques ordres de grandeur et \u00e9quivalences pour mieux appr\u00e9hender cette \u00e9chelle :<\/p>\n<ul data-path-to-node=\"2\">\n<li>\n<p data-path-to-node=\"2,0,0\"><b data-path-to-node=\"2,0,0\" data-index-in-node=\"0\">En kilom\u00e8tres :<\/b> environ <b data-path-to-node=\"2,0,0\" data-index-in-node=\"24\">643,3 milliards de kilom\u00e8tres<\/b> (<span class=\"math-inline\" data-math=\"6,433 \\times 10^{14}\\text{ km}\" data-index-in-node=\"55\">$6,433 \\times 10^{14}\\text{ km}$<\/span>).<\/p>\n<\/li>\n<li>\n<p data-path-to-node=\"2,1,0\"><b data-path-to-node=\"2,1,0\" data-index-in-node=\"0\">En unit\u00e9s astronomiques (UA) :<\/b> environ <b data-path-to-node=\"2,1,0\" data-index-in-node=\"39\">4,3 millions d&#8217;UA<\/b> (la distance Terre-Soleil).<\/p>\n<\/li>\n<li>\n<p data-path-to-node=\"2,2,0\"><b data-path-to-node=\"2,2,0\" data-index-in-node=\"0\">En parsecs :<\/b> environ <b data-path-to-node=\"2,2,0\" data-index-in-node=\"21\">20,85 parsecs<\/b>.<\/p>\n<\/li>\n<\/ul>\n<p data-path-to-node=\"3\"><b data-path-to-node=\"3\" data-index-in-node=\"0\">\u00c0 titre de comparaison dans l&#8217;Univers :<\/b><\/p>\n<ul data-path-to-node=\"4\">\n<li>\n<p data-path-to-node=\"4,0,0\"><b data-path-to-node=\"4,0,0\" data-index-in-node=\"0\">\u00c9toiles connues dans cette zone :<\/b> C&#8217;est une distance tr\u00e8s proche \u00e0 l&#8217;\u00e9chelle de notre Galaxie (la Voie lact\u00e9e fait environ 100 000 al de diam\u00e8tre). Par exemple, l&#8217;\u00e9toile brillante <b data-path-to-node=\"4,0,0\" data-index-in-node=\"180\">Ald\u00e9baran<\/b> (dans la constellation du Taureau) se trouve \u00e0 environ 65 ann\u00e9es-lumi\u00e8re, ce qui est tr\u00e8s proche de cette valeur.<\/p>\n<\/li>\n<li>\n<p data-path-to-node=\"4,1,0\"><b data-path-to-node=\"4,1,0\" data-index-in-node=\"0\">Proxima du Centaure :<\/b> L&#8217;\u00e9toile la plus proche du Soleil se situe \u00e0 4,24 al, soit environ 16 fois plus pr\u00e8s.<\/p>\n<\/li>\n<li>\n<p data-path-to-node=\"4,2,0\"><b data-path-to-node=\"4,2,0\" data-index-in-node=\"0\">D\u00e9calage temporel :<\/b> Si vous observez aujourd&#8217;hui une exoplan\u00e8te ou une \u00e9toile situ\u00e9e \u00e0 68 ann\u00e9es-lumi\u00e8re, vous la voyez telle qu&#8217;elle \u00e9tait il y a 68 ans (la lumi\u00e8re \u00e9mise au milieu du XXe si\u00e8cle ne nous parvient que maintenant).<\/p>\n<p data-path-to-node=\"0\">Une <b data-path-to-node=\"0\" data-index-in-node=\"4\">ann\u00e9e-lumi\u00e8re (al)<\/b> mesure une <b data-path-to-node=\"0\" data-index-in-node=\"34\">distance<\/b>, et non un temps. C&#8217;est la longueur exacte que parcourt un rayon de lumi\u00e8re dans le vide pendant une ann\u00e9e terrestre, soit environ <b data-path-to-node=\"0\" data-index-in-node=\"174\">9 460 milliards de kilom\u00e8tres<\/b> (<span class=\"math-inline\" data-math=\"9,46 \\times 10^{12}\\text{ km}\" data-index-in-node=\"205\">$9,46 \\times 10^{12}\\text{ km}$<\/span>).<\/p>\n<p data-path-to-node=\"1\">Pour se figurer ce chiffre abstrait, il faut changer d&#8217;\u00e9chelle :<\/p>\n<h3 data-path-to-node=\"4\">1. La vitesse de la lumi\u00e8re comme \u00e9talon<\/h3>\n<p data-path-to-node=\"5\">La lumi\u00e8re voyage \u00e0 <b data-path-to-node=\"5\" data-index-in-node=\"20\">300 000 km\/s<\/b>. \u00c0 cette vitesse :<\/p>\n<ul data-path-to-node=\"6\">\n<li>\n<p data-path-to-node=\"6,0,0\"><b data-path-to-node=\"6,0,0\" data-index-in-node=\"0\">Terre \u2013 Lune :<\/b> 1,3 seconde de voyage (384 000 km).<\/p>\n<\/li>\n<li>\n<p data-path-to-node=\"6,1,0\"><b data-path-to-node=\"6,1,0\" data-index-in-node=\"0\">Terre \u2013 Soleil :<\/b> 8 minutes et 20 secondes (150 millions de km).<\/p>\n<\/li>\n<li>\n<p data-path-to-node=\"6,2,0\"><b data-path-to-node=\"6,2,0\" data-index-in-node=\"0\">Terre \u2013 Pluton :<\/b> environ 5 heures et demi.<\/p>\n<\/li>\n<li>\n<p data-path-to-node=\"6,3,0\"><b data-path-to-node=\"6,3,0\" data-index-in-node=\"0\">1 ann\u00e9e-lumi\u00e8re :<\/b> il faut maintenir cette vitesse vertigineuse pendant <b data-path-to-node=\"6,3,0\" data-index-in-node=\"71\">365 jours d&#8217;affil\u00e9e<\/b>.<\/p>\n<\/li>\n<\/ul>\n<h3 data-path-to-node=\"7\">2. Le temps de voyage avec nos technologies<\/h3>\n<p data-path-to-node=\"8\">Si vous tentiez de parcourir <b data-path-to-node=\"8\" data-index-in-node=\"29\">1 seule ann\u00e9e-lumi\u00e8re<\/b> avec des v\u00e9hicules humains :<\/p>\n<ul data-path-to-node=\"9\">\n<li>\n<p data-path-to-node=\"9,0,0\"><b data-path-to-node=\"9,0,0\" data-index-in-node=\"0\">En avion de ligne (900 km\/h) :<\/b> environ 1,2 million d&#8217;ann\u00e9es.<\/p>\n<\/li>\n<li>\n<p data-path-to-node=\"9,1,0\"><b data-path-to-node=\"9,1,0\" data-index-in-node=\"0\">Avec la sonde Voyager 1 (17 km\/s, soit 61 000 km\/h) :<\/b> environ 17 500 ans.<\/p>\n<\/li>\n<\/ul>\n<p data-path-to-node=\"10\">Pour atteindre l&#8217;\u00e9toile <b data-path-to-node=\"10\" data-index-in-node=\"24\">Ald\u00e9baran<\/b> (\u00e0 65-68 ann\u00e9es-lumi\u00e8re), il faudrait plus d&#8217;un million d&#8217;ann\u00e9es \u00e0 Voyager 1.<\/p>\n<div class=\"attachment-container search-images\"><\/div>\n<h3 data-path-to-node=\"13\">3. L&#8217;\u00e9chelle dans la Galaxie<\/h3>\n<p data-path-to-node=\"14\">\u00c0 l&#8217;\u00e9chelle cosmique, 68 ou 368 ann\u00e9es-lumi\u00e8re restent des distances de \u00ab banlieue tr\u00e8s proche \u00bb :<\/p>\n<table data-path-to-node=\"15\">\n<thead>\n<tr>\n<td><strong>\u00c9tape<\/strong><\/td>\n<td><strong>Distance en ann\u00e9es-lumi\u00e8re<\/strong><\/td>\n<\/tr>\n<\/thead>\n<tbody>\n<tr>\n<td><span data-path-to-node=\"15,1,0,0\"><b data-path-to-node=\"15,1,0,0\" data-index-in-node=\"0\">Proxima du Centaure<\/b> (\u00e9toile la plus proche)<\/span><\/td>\n<td><span data-path-to-node=\"15,1,1,0\">4,24 al<\/span><\/td>\n<\/tr>\n<tr>\n<td><span data-path-to-node=\"15,2,0,0\"><b data-path-to-node=\"15,2,0,0\" data-index-in-node=\"0\">Voisinage solaire proche<\/b> (Ald\u00e9baran, 68 al)<\/span><\/td>\n<td><span data-path-to-node=\"15,2,1,0\">68 al<\/span><\/td>\n<\/tr>\n<tr>\n<td><span data-path-to-node=\"15,3,0,0\"><b data-path-to-node=\"15,3,0,0\" data-index-in-node=\"0\">Amas des Pl\u00e9iades<\/b><\/span><\/td>\n<td><span data-path-to-node=\"15,3,1,0\">~440 al<\/span><\/td>\n<\/tr>\n<tr>\n<td><span data-path-to-node=\"15,4,0,0\"><b data-path-to-node=\"15,4,0,0\" data-index-in-node=\"0\">Centre de la Voie lact\u00e9e<\/b><\/span><\/td>\n<td><span data-path-to-node=\"15,4,1,0\">~26 000 al<\/span><\/td>\n<\/tr>\n<tr>\n<td><span data-path-to-node=\"15,5,0,0\"><b data-path-to-node=\"15,5,0,0\" data-index-in-node=\"0\">Diam\u00e8tre total de la Voie lact\u00e9e<\/b><\/span><\/td>\n<td><span data-path-to-node=\"15,5,1,0\">~100 000 al<\/span><\/td>\n<\/tr>\n<tr>\n<td><span data-path-to-node=\"15,6,0,0\"><b data-path-to-node=\"15,6,0,0\" data-index-in-node=\"0\">Galaxie d&#8217;Androm\u00e8de<\/b> (galaxie voisine)<\/span><\/td>\n<td><span data-path-to-node=\"15,6,1,0\">2,5 millions d&#8217;al<\/span><\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<h3 data-path-to-node=\"16\">4. L&#8217;effet \u00ab machine \u00e0 remonter le temps \u00bb<\/h3>\n<p data-path-to-node=\"17\">Regarder loin dans l&#8217;espace revient \u00e0 regarder loin dans le pass\u00e9. La lumi\u00e8re mettant du temps \u00e0 se d\u00e9placer, observer un objet situ\u00e9 \u00e0 <b data-path-to-node=\"17\" data-index-in-node=\"136\">68 ann\u00e9es-lumi\u00e8re<\/b> signifie voir la lumi\u00e8re qui a quitt\u00e9 cet astre il y a 68 ans. Si cet objet explosait aujourd&#8217;hui, nous ne le verrions qu&#8217;apr\u00e8s 68 ans d&#8217;attente.<\/p>\n<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>Une distance de 68 ann\u00e9es-lumi\u00e8re correspond au trajet parcouru par la lumi\u00e8re dans le vide&#8230;<\/p>\n","protected":false},"author":1,"featured_media":2904,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[1077],"tags":[2973,2976,2975,2974,3004,3006,2945,2989,2972,2949,2982,2983,2946,2996,2980,2981,2999,2986,2941,2955,2943,2978,2966,2968,2969,2970,2967,2953,2991,2993,296,2957,2990,2985,2947,2948,2950,2952,2951,2960,2962,2961,2963,2964,2984,3001,2998,3002,2995,2997,3005,3003,2942,2956,2971,2987,2965,2944,2977,2954,2992,2994,3000,2958,2959,2988,2979],"class_list":["post-2903","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-astronomie-agenda","tag-amas-detoiles","tag-amas-de-galaxies","tag-amas-globulaire","tag-amas-ouvert","tag-aphelie","tag-apoastre","tag-asteroide","tag-aurore-polaire","tag-blazar","tag-bolide","tag-ceinture-dasteroides","tag-ceinture-de-kuiper","tag-comete","tag-decalage-vers-le-rouge-redshift","tag-disque-daccretion","tag-disque-protoplanetaire","tag-eclipse","tag-energie-noire","tag-etoile","tag-etoile-a-neutrons","tag-exoplanete","tag-filament-cosmique","tag-galaxie","tag-galaxie-elliptique","tag-galaxie-irreguliere","tag-galaxie-naine","tag-galaxie-spirale","tag-geante-rouge","tag-heliosphere","tag-kilonova","tag-lune","tag-magnetar","tag-magnetosphere","tag-matiere-noire","tag-meteore","tag-meteorite","tag-naine-blanche","tag-naine-brune","tag-naine-rouge","tag-nebuleuse","tag-nebuleuse-demission","tag-nebuleuse-de-reflexion","tag-nebuleuse-obscure","tag-nebuleuse-planetaire","tag-nuage-doort","tag-occultation","tag-ombre","tag-orbite","tag-parallaxe","tag-penombre","tag-periastre","tag-perihelie","tag-planete","tag-pulsar","tag-quasar","tag-rayonnement-fossile","tag-remanent-de-supernova","tag-satellite-naturel","tag-superamas-de-galaxies","tag-supergeante-rouge","tag-supernova","tag-sursaut-gamma","tag-transit","tag-trou-noir","tag-trou-noir-supermassif","tag-vent-solaire","tag-vide-cosmologique"],"jetpack_publicize_connections":[],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"https:\/\/www.laurensoff.com\/wordpress\/wp-content\/uploads\/2026\/09\/Dscn2823-Wurlitzer-3500-Zodiac-On-1.jpg","_links":{"self":[{"href":"https:\/\/www.laurensoff.com\/wordpress\/wp-json\/wp\/v2\/posts\/2903","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.laurensoff.com\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.laurensoff.com\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.laurensoff.com\/wordpress\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.laurensoff.com\/wordpress\/wp-json\/wp\/v2\/comments?post=2903"}],"version-history":[{"count":1,"href":"https:\/\/www.laurensoff.com\/wordpress\/wp-json\/wp\/v2\/posts\/2903\/revisions"}],"predecessor-version":[{"id":2905,"href":"https:\/\/www.laurensoff.com\/wordpress\/wp-json\/wp\/v2\/posts\/2903\/revisions\/2905"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.laurensoff.com\/wordpress\/wp-json\/wp\/v2\/media\/2904"}],"wp:attachment":[{"href":"https:\/\/www.laurensoff.com\/wordpress\/wp-json\/wp\/v2\/media?parent=2903"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.laurensoff.com\/wordpress\/wp-json\/wp\/v2\/categories?post=2903"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.laurensoff.com\/wordpress\/wp-json\/wp\/v2\/tags?post=2903"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}