Pratique du Shadowing: Mars Used to Be Blue... Then Something Happened - Apprendre l'anglais à l'oral avec la vidéo
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The sunset on Mars is not like the sunset on Earth.
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These are color images of Martian sunsets and sunrises, captured by Martian rovers and landers.
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They show us something unexpected.
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The colors of the Martian sky are the opposite of Earth, red in the day and blue near sunset.
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But what's even weirder is that billions of years ago, the daytime sky on Mars was much more like our own.
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In this video, we're going to find out why the Martian sky used to look more like ours, why its sunsets look so strange today,
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and what that has to do with whether Mars may have long ago had life of its own.
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Hey smart people, Joe here.
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Today, Mars is a dusty planet wrapped up in a thin atmosphere that's 95 % carbon dioxide.
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But Mars and Earth once had a lot more in common.
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We've collected a ton of evidence from orbiters, satellites, and rovers that's helped us piece together a picture of a planet that billions of years ago was warmer,
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wetter, and bluer than that dusty red planet we see today.
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Sound familiar?
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To understand why, we have to go back to the beginning.
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Like Earth, Mars formed around 4 .6 billion years ago.
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As clouds of cosmic dust were fused together by gravity, heavier metals sank toward the core.
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The combination of kinetic energy and heat from decaying radioactive elements heated the core of the growing planet into molten iron.
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The movement of molten metal in and around the core generated electric currents.
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And similar to current moving through a wire, all that moving electric charge gave Mars its second similarity to Earth, a magnetic field.
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We know that Mars had a magnetosphere because we found magnetic rocks on Mars' surface.
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You see, these can only be formed if a magnetic field was present as they heated and cooled.
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Those would make the coolest fridge magnets in the solar system.
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The magnetosphere also gave Mars some extra protection from the dangers of space.
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It could deflect streams of particles emitted from the sun and the solar wind.
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The magnetosphere worked like a bubble -wrapped force field to protect Mars' atmosphere
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and the gases in it from being ripped away by that wind.
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But what kinds of gases were in the ancient Martian atmosphere?
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Well, luckily, rocks on the surface of Mars and Martian meteorites found on Earth preserved fingerprints of the ancient Martian atmosphere, like little chemical time capsules.
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By analyzing certain minerals and tiny bubbles of gas, we've learned that Mars used to be surrounded by many of the gases we have in Earth's atmosphere,
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like nitrogen, molecular hydrogen, carbon dioxide, and water vapor.
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These gases would have created a greenhouse effect, absorbing and trapping heat from the surface of Mars, and creating conditions that would have allowed liquid water to form.
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In other words, ancient Mars was quite a bit different from the big red ball of dust and ice we see today.
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When we look closely at the surface of the red planet, we can see evidence of branching river channels,
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dry lake beds, and other formations that look a lot like aquatic systems on Earth.
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Plus, it's still got ice today, which is made of water.
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That didn't just, like, show up by magic.
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And Martian geology gives us clues, too.
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A rare form of quartz, which only forms during highly explosive volcanic eruptions, similar to the one at Mount St. Helens, was picked up by the Curiosity rover,
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here, in the Gale Crater.
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And another mineral, which only forms on Earth in hot underwater events, was found by the Opportunity rover, here.
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These tell us that Mars had an extensive system of massive volcanoes, which pumped out even more of those critical greenhouse gases into the Martian atmosphere,
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so when we follow all those rocky breadcrumbs, they paint a clear picture of a warmer, wetter planet that was pretty similar to Earth.
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And that ancient planet would have shared Earth's famous blue skies and red sunsets, thanks to a phenomenon called Rayleigh scattering.
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When light leaves the sun, it contains all the colors of the rainbow.
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But as those light waves enter the atmosphere, they cause gas molecules in the atmosphere to electromagnetically wiggle.
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And that wiggling scatters the light in different directions.
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But gases in the atmosphere don't scatter all light wavelengths the same.
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The specific gases in the atmosphere of Earth, or ancient Mars, scatter blue light more than the other colors.
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So when light enters the atmosphere like this, blue light from all over here is getting bounced around, so that if you were standing down here,
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the sky above you looks bright blue.
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And since we're subtracting out blue from that white sunlight, that ancient Martian sun would probably even look yellow, just like it does in our own sky.
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But when the sun is near the horizon at sunset, something different happens.
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Sunlight has to travel through a much thicker chunk of atmosphere.
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More of the blues, and even some of the greens are scattered out, leaving just the longer wavelength reds and oranges around where the sun appears.
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And that's why sunsets change the sky from blue to red.
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So, for a long while there, Mars was all blue skies and, I don't know, maybe even rainbows.
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But Mars' blue skies wouldn't last.
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See, sometime after 3 .7 billion years ago, Mars' electromagnetic field switched off.
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We don't find any more magnetic rocks formed on Mars after this time, which equals no more magnetosphere.
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It turns out that if a planet wants to keep its magnetosphere, size matters.
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And unfortunately, Mars is afflicted with little brother energy.
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It's only half the diameter of Earth, and only 11 % of Earth's mass.
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Much like how a small cup of coffee loses its heat a lot faster than a big one, Mars' smaller size made it cool off faster than Earth.
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Its molten core solidified, erasing its electromagnetic force field.
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Now, exposed to the solar wind, Mars' atmosphere was ripped away.
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And without that protective atmosphere, the Martian climate became drier and colder, with only patches of frozen water ice remaining today.
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And Mars went from Earth's brother from another planetary mother… to this.
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Today the Martian atmosphere is much thinner than ours.
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For every hundred molecules of gas that Earth has, Mars has one.
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And instead of those ancient gases, it's full of floating dust particles rich in iron oxides, basically floating powdered rust.
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It's actually all that iron oxide that gives Mars its nickname, the Red Planet.
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But that dust is also the reason the colors of the Martian sky are the opposite of ours today.
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Now, in Rayleigh scattering, the particles doing the scattering have to be way, way smaller than the wavelength of light, things like gas molecules.
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But the dust particles that fill the sky on Mars are about the same size as the wavelengths of light.
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So something else happens.
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It's a process known as me -scattering.
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Here, when light waves collide with larger particles, the waves bend around them, scattering mostly in the forward direction,
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just like how light is scattered around headlights in the fog.
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This kind of scattering doesn't care as much about the color of light, so all colors will get scattered.
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On Earth, it's the reason clouds are white and why dusty days look hazy around the sun.
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Those larger particles of water and dust are scattering light toward our eyes.
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Here on Earth, our dust and water vapor come in all different sizes.
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But when an atmosphere is filled instead with dust particles of a very specific size range, something strange can happen.
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Near sunset on Mars, why do we see this halo of blue light around the sun?
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Recall that Martian dust particles are around the size of visible light wavelengths.
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But those dust particles are a very narrow range of sizes
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that just so happen to have a very tiny preference for ever so slightly scattering blue light forward.
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So near sunset on Mars, as the light travels through a long path of suspended dust,
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that tiny bit of blue scattering leaves a halo filled with more blue light near the Sun.
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And that's why a Martian sunset looks like this.
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This has even happened on Earth after volcanic eruptions, when our own air was full of clouds of fine dust of just that right size,
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leaving silvery -blue halos around the Sun and even the Moon.
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Thanks to decades of exploration of our planetary neighbor, we know that four billion years ago, Mars had blue daytime skies,
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made by ancient geologic processes belching gases into the young planet's atmosphere.
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And this leads us to the biggest question of all.
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Does that mean ancient Mars could have had biological life?
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Just like the fossil record on Earth has helped us understand our own planet's journey from molten rock to pale blue dot.
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Studying the Martian landscape is giving us an even better look into the long history of the now red planet.
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For example, Viking landers did experiments where Martian soil burped out gases when it was fed nutrients.
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That's a process that can be triggered by biological activity.
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And we've found a meteorite containing what looks like mineral grains that bacteria create here on Earth.
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But the biggest clue was uncovered in 2025, when the Perseverance rover collected a rock sample from an ancient riverbed.
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The rock core contains minerals and chemical compounds such as mudstone, organic carbon, sulfur, phosphorus, and oxidized iron.
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When we find those things on Earth, they're linked to biological activity.
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The rover also documented these colorful leopard spots, which are made of minerals that can be produced by microbes.
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Now, if scientists can prove that those minerals can only be formed by living things, that would be a huge hint that Mars once had life.
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Right now, Sapphire Canyon's the strongest evidence we've got that Mars may have had ancient life.
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But, like every other clue that we've found on the red planet, there's a catch.
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Now, on Earth, the artifacts that tell the history of life as we know it, they can't be produced by anything other than life itself.
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On Mars, we still can't be so sure.
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Soil can produce gas, minerals can form in meteorites, and leopard spots can show up in rocks because of life doing its thing.
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But all of these things can also be caused by chemical reactions and geological processes that have nothing to do with life.
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So we still have a lot of ground to cover, literally
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if we want to figure out if Mars was once Earth's living, breathing cousin.
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The good news is, we haven't even explored most of Mars.
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While orbiters have mapped almost all the surface, 99 % of it remains unexplored on the ground.
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From rocks to riverbeds to sunsets, we've been slowly piecing together a picture of what Mars was like a long time ago.
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And as technology improves, maybe we'll find evidence of life on the red planet.
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Or maybe we won't.
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But it'll be worth the search.
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Stay curious.
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Alright, rolling.
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I love how they fall apart at the end.
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But those buttons...
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I made that last line up.
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How about that?
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Nailed it.
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Vocabulaire et conseils d’expression pour cette leçon
Cette leçon d’expression orale de niveau B2 s’appuie sur la vidéo « Mars Used to Be Blue... Then Something Happened ». Les mots qui reviennent le plus souvent : Mars, Earth, Martian, atmosphere, blue. Cette vidéo contient 140 phrases et 2125 mots à répéter en shadowing. La partie parlée dure 12:23. Le locuteur parle à un rythme naturel d’environ 172 mots par minute, proche d’une conversation courante. Seuls 76 % des mots font partie des 3 000 mots les plus courants en anglais, le vocabulaire est donc exigeant.
Vocabulaire clé de cette vidéo
Les 15 mots les plus avancés de la vidéo, avec leur prononciation et leur sens :
| Mot | Prononciation | Sens |
|---|---|---|
| scatter verbe | /ˈskætɚ/ | se disperser, disperser |
| sunset nom | /ˈsʌnˌsɛt/ | coucher de soleil |
| particle nom | /ˈpɑɹtək(ə)l/ | particule |
| mineral nom | /ˈmɪn.ə.ɹəl/ | minéral |
| magnetosphere nom | /mæɡˈni.təˌsfɪr/ | magnétosphère |
| wavelength nom | /ˈweɪvˌlɛŋ(k)θ/ | longueur d'onde |
| melt verbe | /mɛlt/ | fondre, se dissoudre |
| magnetic adjectif | /mæɡˈnɛtɪk/ | magnétique |
| molecule nom | /ˈmɑ.lɪ.kjul/ | molécule |
| dusty adjectif | /ˈdʌsti/ | poussiéreux |
| clue nom | /kluː/ | indice |
| lander nom | [ˈlændɚ] | atterrisseur |
| meteorite nom | /ˈmi.ti.əˌɹaɪt/ | météorite |
| eruption nom | /ɪˈɹʌpʃən/ | éruption |
| vapor nom | /ˈveɪpɚ/ | vapeur |
Les verbes à particule que vous entendrez
| Mot | Prononciation | Sens |
|---|---|---|
| find out verbe | découvrir, savoir | |
| check out verbe | mater, regarder | |
| figure out verbe | cerner | |
| pick up verbe | soulever | |
| set up verbe | /ˌsɛt ˈʌp/ | mettre en place, installer |
| show up verbe | apparaître, se montrer se pointer | |
| switch off verbe | éteindre | |
| turn out verbe | se finir, se terminer |
La grammaire de cette vidéo
Les structures que le locuteur utilise le plus, avec les mots exacts de la vidéo :
| Structure | Dans la vidéo |
|---|---|
| « Used to » used to + verbe — une habitude ou un état passé qui n’est plus vrai | used to look · used to be |
| Voix passive be + participe passé — l’accent est mis sur ce qui arrive, pas sur qui le fait | were fused · be formed · being ripped |
| Present perfect have/has + participe passé — une action passée qui compte encore maintenant | We've collected · we've learned · has even happened |
| Propositions relatives who / which + proposition — une précision sur une personne ou une chose | today, which is · spots, which are · everyone who supports |
Prononciation à surveiller
Le locuteur utilise 23 contractions et formes réduites, comme we've, don't, can't. Prononcez-les sous leur forme courte, telles que vous les entendez.
- Les sons « sh » et « zh »: eruption /ɪˈɹʌpʃən/, dashboard /ˈdæʃˌboɹd/, benchmark /ˈbɛn(t)ʃmɑːk/, coordination /kəʊˌɔːdɪˈneɪʃən/, exploration /ˌɛkspləˈɹeɪʃən/
- Mots longs — placez bien l’accent: magnetosphere /mæɡˈni.təˌsfɪr/, meteorite /ˈmi.ti.əˌɹaɪt/, planetary /ˈplænɪˌtɛəri/, electromagnetic /ɪˌlɛk.tɹoʊ.mæɡˈnɛ.tɪk/, geologic /ˌd͡ʒi.əˈlɑdʒ.ɪk/
Les sons difficiles pour les francophones :
- /h/ — il se souffle, il n’est pas muet: greenhouse /ˈɡɹːnˌ(h)aʊs/, hydrogen /ˈhaɪdɹəd͡ʒ(ə)n/, horizon /həˈɹaɪ.zən/, hint /hɪnt/
- /tʃ/ et /dʒ/ — à ne pas adoucir en « ch » et « j »: geologic /ˌd͡ʒi.əˈlɑdʒ.ɪk/, chunk /t͡ʃʌŋk/, nitrogen /ˈnaɪ.tɹə.d͡ʒən/, geology /d͡ʒɪˈɒl.ə.d͡ʒɪ/, geological /ˌd͡ʒi.əˈlɑdʒ.ɪk.əl/
- /r/ anglais — langue recourbée, sans frotter la gorge: particle /ˈpɑɹtək(ə)l/, mineral /ˈmɪn.ə.ɹəl/, rover /ˈɹoʊvɚ/, magnetosphere /mæɡˈni.təˌsfɪr/, meteorite /ˈmi.ti.əˌɹaɪt/
Comment s’entraîner avec cette vidéo
- Écoutez la vidéo en entier une fois sans parler et notez les mots que vous ne connaissez pas.
- Commencez à la vitesse 0,75×, répétez phrase par phrase, puis revenez à la vitesse normale quand cela devient facile.
- Enregistrez-vous et comparez avec l’original, en faisant attention à des mots comme scatter, sunset, particle.
Qu'est-ce que la technique du Shadowing ?
Le Shadowing est une technique d'apprentissage des langues fondée sur la science, développée à l'origine pour la formation des interprètes professionnels. Le principe est simple mais puissant : vous écoutez de l'anglais natif et le répétez immédiatement à voix haute — comme une ombre suivant le locuteur avec un décalage de 1 à 2 secondes. Les recherches montrent une amélioration significative de la précision de la prononciation, de l'intonation, du rythme, des liaisons, de la compréhension orale et de la fluidité.