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  • Hey it's me Destin. Welcome back to Smarter Every Day. So did you know that in the 60s and 70s

    嘿,這是我Destin。歡迎回到 "每天更聰明"。所以,你知道,在60年代和70年代。

  • when the astronauts went to the moon in the Saturn 5 rocket, they actually


  • left experiments on the surface of the moon? In fact there's one that's still there today


  • and it's still operating. We're still getting data out of it. But before I explain that,


  • I kind of need to go to the bathroom. [Toilet Flush]


  • Alright. Here where I went to grad school we shared this building with NASA, which is interesting because every time I

    好吧,我在這裡讀研究所學生的地方在這裡,我去了研究生院 我們共享這個建築與美國宇航局, 這是有趣的,因為每一次我

  • go wash my hands after using the bathroom, I think about the moon. Check this out.


  • On one wall we have a mirror, and on the other wall we have a mirror and they're lined up.


  • Now all this makes for some pretty interesting fun stuff, but what I want to talk about today


  • is right here. Look at that. No matter where you go in the room,


  • you always see the camera lens right in the corner of the mirror. This has pretty


  • serious implications for NASA science on the moon. Now it's so important


  • that I've asked Henry from MinutePhysics to explain it to you. Let's check it out.


  • (Henry) A corner reflector like this one is an ingenious and beautifully


  • simple device. It takes advantage of the fact that a mirror mirrors one dimension


  • of the world. If you have a second mirror, you can reverse back to how you started.


  • But if the second mirror is at 90 degrees to the first, now when you mirror back,


  • the world will have rotated 180 degrees. So if you send a beam of light


  • into a corner reflector, regardless of what direction you send it in or what direction the


  • corner reflector is oriented, itll come back rotated 180 degrees into a

    角反射器的方向,它將回來旋轉180度成為一個 "角反射器"。

  • parallel return path to its source. (Destin) If you look here at the top of the camera you can see that my name


  • is mirrored. But if I bring it over here to the side in the corner,


  • look at that. You can read it. You can probably see it a little bit better with my shirt.


  • Can't read it.. Now you can. That's because you're seeing a reflection of a reflection.


  • But look at this. If I look back at the corner and then I tilt the camera up,


  • I'm no longer aligned. I can't see the lens any more. Now that tells me that I'm not

    我不再對準了 I'm no longer aligned.我不能'看鏡頭了。現在,這告訴我,我不。

  • in a true return path like he tried to explain to me. (Henry) That's because those mirrors are


  • only reflecting in the two horizontal directions. There's no mirror reflecting back to you


  • in the vertical direction. If you have a third mirror at a right angle, everything will


  • be mirrored, reversed, and mirrored again, so your name will be backwards.


  • But at least now you can move your camera or eyes around however you want,


  • and as long as you can still see all three mirrors, youll see a reflection of yourself


  • in the middle. Mathematically, if you want to reverse a vector, you need to reverse each of its components,


  • and so you need three mirrors to get full retroreflection in 3D.


  • One mirror for each dimension. (Destin) Oh. This is just like the reflectors on the road.

    每個維度都有一面鏡子。(Destin) Oh.這就像路上的反光鏡一樣 This is just like the reflectors on the road.

  • If you look real close at this one that my wife hit with the lawn mower you can see that they're actually


  • just little bitty corner reflectors. (Henry) Exactly! But those are imperfect.

    只是小小的角落反射器(亨利) 沒錯!但這些都是不完美的.

  • On purpose, because a high precision corner reflector would bounce the light back


  • to your car's headlights and not your eyes. (Destin) Ohh! Well I just happen to have


  • an array of high precision corner reflectors here with me in Germany. And what's that?


  • It's Johan, the laser guy from the Netherlands. You remember him right?

    我是Johan 來自荷蘭的那個脈衝光男。你還記得他吧?

  • This corner reflector is so precise,


  • I can set it here on this bridge, go all the way up river to the next bridge,


  • hit it with a laser and I'll still get a reflection, even though it's snowing.


  • Check it out.


  • What are you doing Johan?!


  • (Johan) I'm warming up my laser. (Destin) [laughs] Alright.


  • And ah.. Why are you doing that? - To get it to the right temperature.

    你為什麼要這麼做?- 為了讓它達到合適的溫度。

  • Because it's very temperature sensitive. - Oh OK. Alright can you ping

    因為它對溫度非常敏感。- 哦,好吧。好吧,你可以PING

  • the reflector? There it is. Clearly you're


  • getting a return. That's what? Like 500 meters away would you say? - 350

    得到回報。那是什麼?像500米遠你會說?- 350

  • - How do you know that? - I counted steps. [laugh]

    - 你怎麼知道的?- 我數過步數。[笑]

  • - OK so here's the question. If Johan is able to get a really good reflection

    - 好吧,所以這裡'的問題。如果Johan能夠得到一個非常好的反映。

  • at 350 metres away, in the snow, with a hand-held laser


  • that he's having to blow on to keep alive, then what are we able to do if we put


  • a high precision laser reflector on the moon. In fact,


  • that's what Apollo did. What was it, Apollo what? - 11, 14 and 15.


  • - Apollo 11, 14 and 15. They put retro-reflectors on the moon

    - 阿波羅11號、14號和15號他們在月球上安裝了逆向反射器。

  • and we're still using it for experiments to this day.


  • (Henry) Right. Experiments like monitoring the distance to the moon. If you count how long it takes a photon

    (亨利) 對像監測到月球的距離這樣的實驗。如果你計算一個光子需要多長時間...

  • to get to the moon and back, you can just multiply by the speed of light, divide by two


  • and figure out the distance to the moon, within centimeters. (Destin) Exactly Henry.

    並計算出到月球的距離,在釐米之內。(Destin) 正是亨利。

  • So if you shoot the moon with a laser...

    所以,如果你用脈衝光射向月球... ...

  • 2.56 seconds later, divided by two, 1.28 light


  • seconds to the moon. So if you do the math that ends up to about... this far from the Earth.

    到月球的時間是幾秒鐘所以,如果你計算一下,最後大約... ...離地球這麼遠。

  • (Henry) Anyway, this is useful for understanding the detailed nuances of the


  • moon’s rotation and orbit, measuring movement of tectonic plates here on earth,


  • and even testing the fundamental principles of general relativity. (Destin) Corner reflectors are not


  • just used in optics, you can also use it for any type of reflected electromagnetic radiation.


  • Here, in Frankfurt Germany, there's a bridge with long


  • posts coming off the big pylons there under the bridge. We've got a big boat


  • about to go under the bridge. So if you look at the very end, there's corner reflectors. Only they're not


  • mirrors, they're just metal. He's using a radar to guide


  • off of those corner reflectors so he doesn't hit the bridge. It's basically


  • a passive lighthouse, only it's not light, it's radar.


  • (Henry) Cool! So corner reflectors are like a lighthouse that tells you its distance,

    (亨利) 酷!所以角反射器就像燈塔一樣,可以告訴你它的距離。

  • except better because they don’t need their own source of power. That’s why they were a good experiment to leave


  • on the moon. Actually, the Apollo astronauts left other junk on the moon too.


  • Come over to my channel, MinutePhysics, and I’ll tell you all about it.


  • [Music]


  • That's how the Apollo guys went to the bathroom, in the command module.


  • How'd they do it on the lunar module? (Henry) Imagine it's fairly similar.


  • They probably left it on the moon though. Do you realise there might be.. - There might be poop on the moon. We gotta think this through! [laugh]


  • I didn't even think about that. We always talk about the other


  • stuff that they sent. (Henry) Did they leave their poop on the moon? [laughs]


  • I imagine they must have, because like why would you bring that back? - When I go hiking I try to find the perfect

    我想他們一定有,因為像你為什麼要把它帶回來?- 當我去遠足,我試圖找到完美的。

  • spot. That guy has won that game. [laugh]


  • (Henry) The most distant porta-john. [laugh] The most distant porta-john is the


  • on the lunar landers on the moon.


  • [ Captions by Andrew Jackson ]


  • Captioning in different languages welcome. Please contact Destin if you can help.


Hey it's me Destin. Welcome back to Smarter Every Day. So did you know that in the 60s and 70s

嘿,這是我Destin。歡迎回到 "每天更聰明"。所以,你知道,在60年代和70年代。

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