page_title: Adaptive optics
section_title: Natural guide stars
hierarchical_section_title: Adaptive optics / In astronomy / Using guide stars / Natural guide stars
caption_attribution_description: Česky: Pozorování Mléčné dráhy na observatoři Paranal v srpnu 2010 pomocí laserové korekce. Deutsch: Mitte August 2010 schoss der ESO-Fotobotschafter Yuri Beletsky dieses Foto des Paranal-Observatoriums der ESO. Eine Gruppe von Astronomen beobachtete das Zentrum der Milchstraße unter Verwendung der Vorrichtung zur Erzeugung eines künstlichen Leitsterns mit dem Yepun-Teleskop, einem der vier Unit-Teleskope des Very Large Telescope (VLT). Yepuns Laserstrahl durchquert den südlichen Himmel und erzeugt einen künstlichen Stern in 90&#160;km Höhe in der Mesosphäre der Erde. Der Laser-Leitstern (LGS) ist ein Teil der adaptiven Optik des VLT und wird als Referenz zur Korrektur der durch die Atmosphäre verursachten Unschärfe-Effekte auf Aufnahmen verwendet. Die Farbe des Lasers ist exakt abgestimmt, um eine Schicht von Natrium-Atomen anzuregen, die sich in einer der oberen Schichten der Atmosphäre befindet&#160;– die bekannte Farbe der Natrium-Lampen der Straßenbeleuchtung lässt sich in der Farbe des Lasers wiedererkennen. Vermutlich ist diese Schicht von Natrium-Atomen ein Überrest von Meteoriten, die in die Erdatmosphäre eintreten. Wenn sie durch das Licht des Lasers angeregt werden, beginnen die Atome zu leuchten und bilden so einen kleinen hellen Fleck, der als künstlicher Referenzstern für die adaptive Optik benutzt werden kann. Mittels dieser Technik können Astronomen schärfere Beobachtungsergebnisse erhalten. Beispielsweise können Forscher bei der Beobachtung des Zentrums unserer Milchstraße besser den galaktischen Kern überwachen. In diesem verschluckt ein supermassereiches schwarzes Loch Gas und Staub, während es von nahen Sternen umkreist wird. Das Foto wurde mit einem Weitwinkelobjektiv aufgenommen und deckt mit etwa 180° beinahe den gesamten sichtbaren Himmel ab. English: In mid-August 2010 ESO Photo Ambassador Yuri Beletsky snapped this photo at ESO’s Paranal Observatory, Chile. A group of astronomers were observing the centre of the Milky Way using the laser guide star facility at Yepun, one of the four Unit Telescopes of the Very Large Telescope (VLT). Yepun’s laser beam crosses the southern sky and creates an artificial star at an altitude of 90 km high in the Earth's mesosphere. The Laser Guide Star (LGS) is part of the VLT’s adaptive optics system and is used as a reference to correct the blurring effect of the atmosphere on images. The colour of the laser is precisely tuned to energise a layer of sodium atoms found in one of the upper layers of the atmosphere — one can recognise the familiar colour of sodium street lamps in the colour of the laser. This layer of sodium atoms is thought to be a leftover from meteorites entering the Earth’s atmosphere. When excited by the light from the laser, the atoms start glowing, forming a small bright spot that can be used as an artificial reference star for the adaptive optics. Using this technique, astronomers can obtain sharper observations. For example, when looking towards the centre of our Milky Way, researchers can better monitor the galactic core, where a central supermassive black hole, surrounded by closely orbiting stars, is swallowing gas and dust. Taken with a wide angle lens, this photo covers about 180° of the sky. Français: Utilisation d'un laser pour observer en détail le centre galactique. Le laser provoque la formation d'une «&#160;étoile artificielle&#160;» dans la mésosphère, à 90 km d'altitude. Cette source de lumière est utilisée comme référence pour compenser les turbulences atmosphériques. Le laser est réglé sur la fréquence d'excitation du sodium. Sa couleur jaune rappelle d'ailleurs celle des lampes à sodium utilisées dans l'éclairage urbain. Cette couche de sodium dans la mésosphère serait une trace laissée par les météorites qui la traversent. Cette méthode permet d'étudier en détail des détails fins du ciel, tels que l'activité du trou noir se trouvant dans le centre galactique, objet de l'étude menée ici. Photo prise à la mi-août 2008 au VLT sur le Cerro Paranal, au Chili. La photo, prise avec un grand angle, couvre 180°. Galego: Foto tomada a mediados de agosto de 2010 por Yri Beletsky nas instalacións de Yepun, unha das catro instalacións telescópicas do VLT (siglas inglesas de Telescopio Moi Grande) do ESO (siglas inglesas do gl:Observatorio Espacial Europeo) de Cerro Paranal (Chile). A foto está tomada cun grande angular, que cobre arredor de 180º da bóveda celeste. Nela pode verse o uso dun láser para observar detalladamente o centro da nosa galaxia, a Vía Láctea. O láser provoca a creación dunha estrela artificial na mesosfera a 90 km de altitude, debido a que está sincronizado coa frecuencia de exticatión do sodio. Por iso, a súa cor amarela-laranxa lembra ás lámpadas de sodio usadas na iluminación urbana. Suponse que esta capa de átomos de sodio son os restos dos meteoritos que entran na atmosfera terrestre. Cando se excitan pola luz do láser, os átomos comezan a brillar formando un punto rechamante que pode usarse como unha estrela artificial de referencia para calibrar os sistemas ópticos: usando este sitema, os astrónomos poden obter observacións máis exactas. Por exemplo: cando se observa o centro da nosa galaxia, os investigadores poden controlar mellor o núcleo galáctico, onde un burato negro central supermasivo rodeado de estrelas orbitando moi preto, absorbe gas e po. Italiano: Il 6 agosto 2010, il Photo Ambassador dell'ESO, Yuri Beletsky, ha scattato questa fotografia all'Osservatorio astronomico del Paranal in Chile, dove un gruppo di astronomi stava osservando il centro della Via Lattea usando uno dei quattro telescopi ottici (chiamato "Yepun") del Very Large Telescope (VLT). Il raggio laser di Yepun attraversa il cielo australe e crea una stella artificiale ad un'altitudine di 90 chilometri, all'altezza della mesosfera della Terra. Questa Laser Guide Star (LGS) è parte del sistema ottico adattivo del VLT ed è usata come riferimento per correggere l'effetto blur dell'atmosfera sulle immagini. Il colore del laser è calibrato precisamente per energizzare uno strato di atomi di sodio che si trova in uno degli strati superiori dell'atmosfera — si può riconoscere il familiare colore dei lampioni stradali, che usano lampade al sodio. Si pensa che questo strato di atomi di sodio sia un residuo lasciato da meteoriti penetrati nell'atmosfera terrestre. Quando eccitati dalla luce emessa dal laser, gli atomi iniziano a brillare, formando un piccolo punto luminoso che può essere usato come stella artificiale di riferimento dall'ottica adattiva. Usando questa tecnica, gli atronomi possono ottenere osservazioni più precise. Per esempio, quando si osserva il centro della Via Lattea, i ricercatori possono monitorare meglio il centro galattico, dove un buco nero supermassiccio, circondato a breve distanza da stelle orbitanti, ingoia gas e polveri. Scattata con lenti panoramiche, questa fotografia copre il cielo a circa 180°. Türkçe: 2010'un Ağustos ayında ESO Fotoğraf Büyükelçisi Yuri Beletsky ESO'nun Paranal Gözlemevi'nde bu inanılmaz fotoğrafı çekti. Bir grup gökbilimci Yepun (Çok Büyük Teleskop (VLT)'un dört teleskobundan biri)'un lazer kılavuz özelliğini kullanarak Samanyolu'nun merkezini gözlemledi. Tiếng Việt: Chiếu tia laser hướng về tâm của Ngân Hà từ một trạm thiên văn đơn vị của hệ thống thiên văn VLT. Русский: В августе 2010 г. группа астрономов наблюдала центр Млечного Пути с использованием лазерного оборудования телескопа Yepun (Венера на языке индейцев Мапуче) (одного из четырех телескопов Очень Большого Телескопа Европейской южной обсерватории (англ. ESO), Обсерватория Паранал, Чили Фото посла ESO Юрия Белецкого. Українська: В серпні 2010 р. група астрономів спостерігала центр Чумацького Шляху з використанням лазерного обладнання телескопа Yepun (Венера мовою індіанців Мапуче) (одного з чотирьох телескопів Дуже Великого Телескопа Європейської південної обсерваторії (англ. ESO), Обсерваторія Паранал, Чилі. Фото посла ESO Юрія Білецького. فارسی: این نگاره را امبسدور یوری بلتسکی در اواسط اوت ۲۰۱۰ گرفته‌است. گروهی از ستاره‌شناسان، مرکز کهکشان راه شیری را توسط ستاره هدایت لیزری در یپون (یکی از چهار عدد از بزرگترین تلسکوپ‌های دنیا) رصد می‌کردند. پرتوی لیزری «یپون» از قسمت جنوبی آسمان عبور می‌کند و ستاره‌ای ساختگی در ۹۰ کیلومتری لایه مزوسفر زمین به وجود می‌آورد. رنگ لیزر برای انرژی دادن به اتم‌های سدیم لایه بالایی اتمسفر تنظیم شده که همان رنگ آشنای لامپ‌های سدیم در خیابان‌ها است. وقتی این اتم‌ها توسط لیزر برانگیخته می‌شوند، شروع به تابش می‌کنند و نقطهٔ نورانی کوچکی را شکل می‌دهند که می‌تواند به عنوان یک ستاره مرجع ساختگی جهت انطباق نورها استفاده شود. با استفاده از این شیوه فناوری ستاره‌شناسان می‌توانند به رصدهای دقیق‌تری دست یابند. برای مثال وقتی به سمت مرکز کهکشان راه شیری نگاه انداخته می‌شود، محققان بهتر می‌توانند هسته کهکشان را ببینند، محلی که یک سیاهچاله فوق بزرگ توسط ستاره‌های که دور آن می‌گردند احاطه شده و گاز و خاکستر به خود جذب می‌کند.
context_page_description: Adaptive optics is a technology used to improve the performance of optical systems by reducing the effect of incoming wavefront distortions by deforming a mirror in order to compensate for the distortion. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, in microscopy, optical fabrication and in retinal imaging systems to reduce optical aberrations. Adaptive optics works by measuring the distortions in a wavefront and compensating for them with a device that corrects those errors such as a deformable mirror or a liquid crystal array.
  Adaptive optics should not be confused with active optics, which works on a longer timescale to correct the primary mirror geometry.
  Other methods can achieve resolving power exceeding the limit imposed by atmospheric distortion, such as speckle imaging, aperture synthesis, and lucky imaging, or by moving outside the atmosphere with space telescopes, such as the Hubble Space Telescope.
context_section_description: Because a science target is often too faint to be used as a reference star for measuring the shape of the optical wavefronts, a nearby brighter guide star can be used instead. The light from the science target has passed through approximately the same atmospheric turbulence as the reference star's light and so its image is also corrected, although generally to a lower accuracy.
  The necessity of a reference star means that an adaptive optics system cannot work everywhere on the sky, but only where a guide star of sufficient luminosity (for current systems, about magnitude 12–15) can be found very near to the object of the observation. This severely limits the application of the technique for astronomical observations. Another major limitation is the small field of view over which the adaptive optics correction is good. As the angular distance from the guide star increases, the image quality degrades. A technique known as "multiconjugate adaptive optics" uses several deformable mirrors to achieve a greater field of view.
caption: A laser beam directed toward the centre of the Milky Way. This laser beam can then be used as a guide star for the AO.
exif: {"Image ImageDescription": "In mid-August 2010 ESO Photo Ambassador Yuri Beletsky snapped this amazing photo at ESO\u2019s Paranal Observatory. A group of astronomers were observing the centre of the Milky Way using the laser guide star facility at Yepun, one of the four Unit Telescopes of the Very Large Telescope (VLT). Yepun\u2019s laser beam crosses the majestic southern sky and creates an artificial star at an altitude of 90 km high in the Earth's mesosphere. The Laser Guide Star (LGS) is part of the VLT\u2019s adaptive optics system and is used as a reference to correct the blurring effect of the atmosphere on images. The colour of the laser is precisely tuned to energise a layer of sodium atoms found in one of the upper layers of the atmosphere \u2014 one can recognise the familiar colour of sodium street lamps in the colour of the laser. This layer of sodium atoms is thought to be a leftover from meteorites entering the Earth\u2019s atmosphere. When excited by the light from the laser, the atoms start glowing, forming a small bright spot that can be used as an artificial reference star for the adaptive optics. Using this technique, astronomers can obtain sharper observations. For example, when looking towards the centre of our Milky Way, researchers can better monitor the galactic core, where a central supermassive black hole, surrounded by closely orbiting stars, is swallowing gas and dust. The photo, which was chosen as Astronomy Picture of the Day for 6 September 2010 and Wikimedia Picture of the Year 2010, was taken with a wide-angle lens and covers about 180 degrees of the sky. \u00a0 This image is available as a mounted image in the ESOshop. \u00a0 #L"}