{"id":2107,"date":"2015-03-12T08:47:51","date_gmt":"2015-03-12T08:47:51","guid":{"rendered":"https:\/\/blogs.futura-sciences.com\/feldmann\/?p=2107"},"modified":"2015-03-18T06:14:41","modified_gmt":"2015-03-18T06:14:41","slug":"insolite-il-neige-lobservatoire-de-la-silla","status":"publish","type":"post","link":"https:\/\/blogs.futura-sciences.com\/feldmann\/2015\/03\/12\/insolite-il-neige-lobservatoire-de-la-silla\/","title":{"rendered":"Insolite : il a neig\u00e9 \u00e0 l’Observatoire de La Silla"},"content":{"rendered":"

Bien que situ\u00e9 dans une des r\u00e9gions les plus s\u00e8ches du monde, l’Observatoire de la Silla<\/a> re\u00e7oit parfois quelques pr\u00e9cipitations sous forme de pluie ou de neige. Mais comment peut-il y avoir des chutes de neige \u00e0 un endroit o\u00f9 la temp\u00e9rature descend tr\u00e8s rarement en dessous de 0\u00b0C ?<\/p>\n

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

La r\u00e9ponse est donn\u00e9e par l’air sec. Les flocons de neige (qui se forment dans des nuages avec des temp\u00e9ratures n\u00e9gatives) descendent dans un air tr\u00e8s sec : une petite partie de chaque flocon s’\u00e9vapore, \u00e9vaporation qui \u00e9limine l’exc\u00e8s de chaleur et permet aux flocons de rester assez froids pour survivre \u00e0 cette descente.<\/p>\n

En somme il peut neiger \u00e0 La Silla quand il fait plus de 0\u00b0C \u00e0 condition que le taux d’humidit\u00e9 pr\u00e9sent dans l’air soit le plus faible possible.<\/p>\n

Ce ph\u00e9nom\u00e8ne physique a pu \u00eatre v\u00e9rifi\u00e9 le 9 mars 2015, jour o\u00f9 cette photographie a \u00e9t\u00e9 prise par Malte Tewes<\/a>, l’un des photographes ambassadeurs de l’ESO. Il n’aura pas fallu longtemps pour que disparaisse cette \u00e9ph\u00e9m\u00e8re pellicule blanche et pour que le site de La Silla retrouve sa physionomie habituelle.<\/p>\n

Notons qu’il est possible d’observer chez nous des chutes de neige quand il fait plus de 0\u00b0C \u00e0 condition que les flocons soient assez gros (ils fondent en surface ce qui acc\u00e9l\u00e8re leur chute et la plupart atteignent le sol), ou que la temp\u00e9rature de l’air ne soit positive qu’\u00e0 moins de 300 m du sol.<\/p>\n

\u00c0 propose de La Silla : c’est \u00e0 2400 m\u00e8tres d’altitude, \u00e0 600 kilom\u00e8tres au nord de Santiago du Chili, que l’Observatoire Europ\u00e9en Austral a implant\u00e9 ses premi\u00e8res coupoles dans les ann\u00e9es 1960. Le plus gros t\u00e9lescope h\u00e9berg\u00e9 sur ce site a un diam\u00e8tre de 3,6 m\u00e8tres. L’ESO dispose en outre d’un site au Paranal (toujours au Chili, \u00e0 2600 m\u00e8tres d’altitude, \u00e0 130 km au sud d’Antofagasta) qui h\u00e9berge ses 4 t\u00e9lescopes g\u00e9ants VLT<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"

Bien que situ\u00e9 dans une des r\u00e9gions les plus s\u00e8ches du monde, l’Observatoire de la Silla re\u00e7oit parfois quelques pr\u00e9cipitations sous forme de pluie ou de neige. Mais comment peut-il y avoir des chutes de neige \u00e0 un endroit o\u00f9 la temp\u00e9rature descend tr\u00e8s rarement en dessous de 0\u00b0C ? La r\u00e9ponse est donn\u00e9e par … Continuer la lecture de Insolite : il a neig\u00e9 \u00e0 l’Observatoire de La Silla<\/span> →<\/span><\/a><\/p>\n","protected":false},"author":8,"featured_media":2108,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","_links_to":"","_links_to_target":""},"categories":[509],"tags":[635,633,892,894,893,96,637],"class_list":["post-2107","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-actualites","tag-chili","tag-eso","tag-observatoire-de-la-silla","tag-paranal","tag-santiago","tag-telescope","tag-vlt"],"yoast_head":"\nInsolite : il a neig\u00e9 \u00e0 l'Observatoire de La Silla<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/blogs.futura-sciences.com\/feldmann\/2015\/03\/12\/insolite-il-neige-lobservatoire-de-la-silla\/\" \/>\n<meta property=\"og:locale\" content=\"fr_FR\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Insolite : il a neig\u00e9 \u00e0 l'Observatoire de La Silla\" \/>\n<meta property=\"og:description\" content=\"Bien que situ\u00e9 dans une des r\u00e9gions les plus s\u00e8ches du monde, l’Observatoire de la Silla re\u00e7oit parfois quelques pr\u00e9cipitations sous forme de pluie ou de neige. 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