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Źródło: https://www.bbc.com/future/article/20260929-why-astronomers-make-fake-stars-with-huge-lasers

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Why astronomers make fake stars with huge lasers

Why astronomers make fake stars with huge lasers

For the first time in its history, the Very Large Telescopeteleskop in Chile is operating with up to seven lasers that fire up into the atmosphereatmosfera. But why do astronomersastronomowie need them?

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If you happened to be wandering Chile's Atacama Desert in the middle of the night, you might encounternapotkać an extraordinaryniezwykły scene: the sight of enormous lasers piercing the skyprzeszywające niebo. From a distance, you'd see them emerging from a sci-fi structurebudowla rodem z filmu science fiction on a mountain top, like the lairkryjówka of an evil villainczarny charakter.  

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Closer up, though, you'd discover the source is actually a telescope – a particularly big one – made up ofskładający się z several buildings. Inside, teams of astronomersastronomowie on the night shift would be positioning the lasers to create an "artificial starsztuczna gwiazda" at the edge of Earth's atmosphereatmosfera.

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If you were passing by this evening, you might catchzobaczyć; przyłapać wzrokiem them firing four lasers from four separate structures on the mountain-top at the same time – which would be a firstco byłoby czymś, co zdarza się po raz pierwszy. 

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This is the Very Large Telescope (VLT) at Paranal – operated by the European Southern Observatoryobserwatorium (Eso) – which the BBC recently visited. In late 2025, engineers there finished installing the last of a series of powerful new lasers to help astronomers peer into the cosmosprzyglądać się kosmosowi with greater fidelitydokładność, taking the total number to seven. But why do telescopes need such lasers in the first placew ogóle; w pierwszej kolejności? 

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The idea for using lasers in astronomyastronomia can be traced backmożna wywodzić to the Cold Warzimna wojna, when the US military developed technology to track Soviet satellitessatelity. Astronomers eventually realised that similar techniquestechniki would help improve their observationsobserwacje from the ground.

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Why? Telescopes on Earth's surface face a barrierprzeszkoda that space telescopes do not: the atmosphere. The gases clingingprzylegające to our planet distortzniekształcać starlightświatło gwiazd before it reaches a ground telescopeteleskop naziemny's mirror. Atmospheric conditions continuallynieustannie change too.  

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"We are protected by our atmosphere, which is fantastic. But as an astronomer it is horrible, because the atmosphere basically messes withzakłóca the sharpnessostrość of the light coming from stars and galaxies," says astronomer Amelia Bayo, a project scientistnaukowiec odpowiedzialny za projekt with Eso who advises on how to get the most from the VLT's instruments. "If you don't compensateskompensować for the atmosphere, your star is going to be jumping in different places of your detectordetektor and you will end up withskończyć z a blurredrozmyty image."

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To get aroundporadzić sobie z this problem, astronomers apply an approach called "adaptive opticsoptyka adaptacyjna". "The implementationwdrożenie is hard, but the idea is super simple," explains Bayo. After the distortedzniekształcone light strikespada na the telescope's primary mirrorlustro główne, it reflects to another smaller mirror that can deformodkształcać się to essentiallyzasadniczo match, and correct, the atmospheric distortionzniekształcenie. 

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In the VLT, one of these adaptive mirrors contains piezoelectricpiezoelektryczny materials – ones which can generate an electric charge – that can change shape at "crazy speeds", says Bayo. The mirror is also suspendedzawieszony inside a magnetic fieldpole magnetyczne. "It's stupidly cool. It is basically floating," she adds.

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For adaptive opticsoptyka adaptacyjna to work, though, astronomers need a star as a reference pointpunkt odniesienia – a fixed point in the sky. And cruciallyco najważniejsze, it needs to be bright. Why? "Imagine that you're listening to a song, and you want to get the melody," explains Bayo. "If the volume is low; if there's more noise, or you only hear high or low pitchwysokość dźwięku, then you may not be able to tell which song it is." It's the same with stars; a bright star provides more information to help correct the atmospheric distortionzniekształcenie obrazu przez atmosferę.

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Sometimes it's possible to use natural stars, but when astronomers look at a part of the sky without any suitablyodpowiednio bright ones, they turn tosięgać po lasers instead. 

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Firing lasers in the direction they are looking exciteswzbudza a sodium-richbogaty w sód layer in the atmosphere, around 90km (56 miles) above the ground. These sodium atoms will then emitemitować photonsfotony that the mirrors back at the telescope can catch. In short, an artificial starsztuczna gwiazda. "Our atmosphere is sodium-richbogaty w sód. It offers a canvaspłótno; tu: przestrzeń, na której można umieścić gwiazdę where we can put the star anywhere we want," says Bayo.

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The lasers now installed at the VLT are state-of-the-artnajnowocześniejszy. Bayo remembers the previous generation were difficult to calibrateskalibrować, requiring toxictoksyczny liquid dyesbarwniki, and days of engineering work to ensure stabilitystabilność. "Before it almost looked like you had a laser pointer you were holding in your shaking hand, and now you have a perfect stable device that launches a laser that is way more powerful." Today, the astronomers simply press a button to launch their laser, and it stays fixed in placenieruchomo ustawiony all night.

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After upgrades in 2016, one of the four 8.2m-long (27ft) telescopes of the VLT (Yepun) gained the ability to fire four lasers simultaneouslyjednocześnie, which allows astronomers to correct atmospheric disturbancezakłócenia atmosferyczne over a wider field of viewpole widzenia. Each laser delivers 22 watts of power – about 4,000 times the maximum allowed for a laser pointer – in a 30cm-wide (12in) diameterśrednica beam.

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As of 2026, the four main telescopes of the VLT (Antu, Kueyen, Melipal and Yepun) can now also combine forcespołączyć siły – in an act of astronomical Power Rangers – to fire lasers at the same time, assemblingłącząc się into a single, giant "virtualwirtualny; pozorny" telescope with a wider field of viewpole widzenia. By working together, the four big mirrors in each of those four telescopes can capture details many times sharper than one alone. 

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The VLT has been responsible for some of the most significant astronomicalastronomiczny discoveries of the 21st Century, including the first image of an extrasolarpozaukładowy planet (one that lives outside of our Solar System), and the positions of individual stars moving around the supermassivesupermasywny black holeczarna dziura at the Milky Way's centre.

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One final question you might wonder: what happens if a plane passes over? After all, even the smallest laser pointers pose a riskstwarzać ryzyko of dazzlingoślepiania pilots. 

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"Planes can of course pass above the observatoryobserwatorium, but we have a safety mechanismmechanizm bezpieczeństwa," explains astronomer Itziar de Gregorio Monsalvo, Eso's representativeprzedstawiciel in Chile. "If the planes cross near where we are observing, automatically the lasers switch offwyłączają się."

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So, that means if you wanted to see a very large telescope firing its very large lasers in the Atacama, you'd probably have to approach on the ground. But if you did, you'd encounter a scene rarely encounterednapotkaną in day-to-day lifecodzienne życie: a telescope lighting upoświetlający an artificialsztuczną star on the edge of our planet's atmosphereatmosfery. 

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