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Speaker 1: Welcome to tech Stuff, a production of I Heart Radios

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Speaker 1: How Stuff Works. Hey there, and welcome to tech Stuff.

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Speaker 1: I'm your host, Jonathan Strickland. I'm an executive producer with

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Speaker 1: How Stuff Works in My Heart Radio and I love

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Speaker 1: all things tech and way back in one a very

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Speaker 1: not good film titled Robin Hood Prince of Thieves debut

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Speaker 1: and don't at me. That movie is trash. I loved

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Speaker 1: it as a kid, but it is garbage. It starred

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Speaker 1: Kevin Costner as Robin of Locksley, better known as the

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Speaker 1: outlaw Robin Hood, and the film is set in eleven

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Speaker 1: ninety four and Robin had a lot of problems. The

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Speaker 1: Sheriff Nottingham was on his back, his beloved made Marian

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Speaker 1: gets kidnapped, and his accent kept going in and out,

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Speaker 1: so you can imagine the stress he was under. But

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Speaker 1: he also had some advance diages. Now, one of those

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Speaker 1: was his ingenious companion a Zeem played by Morgan Freeman.

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Speaker 1: And in one scene, a Zeem helps Robin get a

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Speaker 1: better look at some adversaries using a telescope. Now that

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Speaker 1: scene is meant to establish that a Zeem's homeland often

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Speaker 1: viewed as a backward and savage place through the eyes

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Speaker 1: of England, and by extension, the West in general is

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Speaker 1: actually home to great learning and innovation. And that part

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Speaker 1: was true. I mean, the Middle East has a long

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Speaker 1: history of phenomenal achievements, but inventing a telescope in the

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Speaker 1: late twelfth century is not among them. That was historically inaccurate,

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Speaker 1: probably the least of the historical inaccuracies in that film.

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Speaker 1: But still I wanted to start with this because this

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Speaker 1: was just one of the many fictions and fallacies in

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Speaker 1: The Robin Hood. But I figured it was a fun

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Speaker 1: place to start off this episode about the telescope. We're

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Speaker 1: gonna look at where it actually did come from and

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Speaker 1: how basic telescopes were. I guess you could say it's

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Speaker 1: the focus of this episode. H m hm. And So

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Speaker 1: while I now will leave the film Robin Hood Prince

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Speaker 1: of Thieves behind, just remember that everything I do, I

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Speaker 1: do it for you. Now, As is the case with

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Speaker 1: much of technology, it's not really possible for me to

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Speaker 1: tell you who invented the first telescope. I can tell

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Speaker 1: you that the person most folks credit with inventing the

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Speaker 1: telescope was the German Dutch inventor Hans Lipperty. He applied

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Speaker 1: for a patent for an invention he called the geiker

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Speaker 1: or kaiker. It's kind of hard for me to pronounce

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Speaker 1: because I don't speak Dutch, but it means looker in Dutch.

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Speaker 1: We'll come back to it. For this invention to be

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Speaker 1: possible at all, the first thing that has to happen

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Speaker 1: is that humans needed to learn how to make glass.

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Speaker 1: Now we don't have a record of that actually happened,

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Speaker 1: but our best guess is that glassmaking became an actual

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Speaker 1: thing around four thousand years ago in Mesa Potamia, as

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Speaker 1: the B. Fifty two s would say, a region called Ptolemace,

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Speaker 1: which is in now modern day Israel, was particularly known

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Speaker 1: for this, having sand that was suitable for glassmaking, and

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Speaker 1: early glassmakers would mix sand, soda, and lime which could

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Speaker 1: then be heated in a furnace to create molten glass.

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Speaker 1: To make a solid glass object, this mixture of sand, soda,

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Speaker 1: and lime would first be put into an open mold,

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Speaker 1: and the mold would be placed in the furnace, which

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Speaker 1: would be heated up enough for the mixture to become

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Speaker 1: molten glass. It would fill up this mold. They'd take

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Speaker 1: the mold out and allow it to cool. Now, if

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Speaker 1: you want to make a container something that could hold

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Speaker 1: stuff like a vase or a perfume bottle, the glassmakers

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Speaker 1: used a process called core forming. And yeah, I realized,

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Speaker 1: I'm already getting a little far away from talking about

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Speaker 1: telescopes and lenses. But I also think this process is

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Speaker 1: super neat, so I want to explain it briefly. First,

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Speaker 1: the glassmaker would determine what the interior shape of this

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Speaker 1: object was going to be, so, for talking about a bottle,

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Speaker 1: whether it's going to be tall and narrow, or whether

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Speaker 1: it was going to be a wide jug, something along

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Speaker 1: those lines. Then they would create the core out of

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Speaker 1: a mixture of clay, sand, water, and uh poop or

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Speaker 1: dung if you prefer, and then they would shape that

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Speaker 1: into the rough form they wanted. Before they would insert

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Speaker 1: a metal rod into one end of it, the essentially

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Speaker 1: the end that would be in the open part of

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Speaker 1: the container. They would then allow this core to dry.

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Speaker 1: After it dried, the glassmaker would use tools to further

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Speaker 1: refine the shape of the core, trimming it, filing it down,

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Speaker 1: that kind of thing. Once finalized, Once it's in that

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Speaker 1: final shape, the glassmaker would heat up a mixture of sand, lime,

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Speaker 1: and soda in a crucible in a furnace, creating a

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Speaker 1: molten glass inside that crucible. Then they would insert this

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Speaker 1: core into that molten glass, hold down the metal rod.

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Speaker 1: They would slowly twirl the core within the molten glass,

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Speaker 1: getting a full coating on the core, sort of like

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Speaker 1: coating a candy apple. The glassmaker would then remove this

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Speaker 1: let cool a little bit, and use some other tools

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Speaker 1: like pincers for example, to shape the glass while it

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Speaker 1: was still a pliable and then after it had cooled

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Speaker 1: down a bit, they might reheat it a little to

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Speaker 1: to soften the glass, maybe add different colors of glass

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Speaker 1: as decorations on top of it. You could twirl a

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Speaker 1: line of molten glass on top of another layer, have

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Speaker 1: contrasting colors and decorated that way. You might want to

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Speaker 1: add things like handles to say a pot. Glassmakers would

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Speaker 1: then change the color of the glass, by the way,

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Speaker 1: by by mixing in metal oxides, because different metals would

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Speaker 1: produce different colors. The whole process is super neat to watch.

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Speaker 1: There's actually a lot of videos on YouTube about this process,

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Speaker 1: so if it sounds interesting to you should really check

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Speaker 1: it out because it's pretty neat to see how these

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Speaker 1: ancient glassmakers would make this stuff. Anyway, glass was incredibly

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Speaker 1: useful and it was much sought after, and these early

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Speaker 1: examples I'm talking about we're really interesting. But the glass

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Speaker 1: they produced were not at all suitable for creating any

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Speaker 1: sort of lens. Those would have to wait for a

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Speaker 1: couple of thousand years. But the foundation for it came

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Speaker 1: from a pretty simple observation. Water has a magnifying effect,

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Speaker 1: and humans in the ancient world noticed this and wondered,

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Speaker 1: is there a way we could replicate this, where we

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Speaker 1: could create a way to magnify stuff without having to

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Speaker 1: use water. This led to ancient Egyptians and Mesopotamians experimenting

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Speaker 1: with polished crystals, usually using courts around seven fifty b C.

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Speaker 1: One such lens, the Nimrod lens, was made sometime around

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Speaker 1: then in ancient Assyria. Smartie pants Greek and Roman philosophers

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Speaker 1: began to hypothesize about what was actually going on with

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Speaker 1: these materials, What was creating this magnification effect, how did

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Speaker 1: it really how did it really work? They made some

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Speaker 1: progress over the centuries and sussing things out, but the

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Speaker 1: fall of the Roman Empire would set the world back

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Speaker 1: more than a step or two. A lot of learning

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Speaker 1: was lost, a lot of progress was halted. One place

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Speaker 1: that continued the academic exploration of what was going on

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Speaker 1: in the world of optics was in the Middle East,

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Speaker 1: and this is probably where the Robin Hood crew got

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Speaker 1: their idea for including a telescope in their screenplay. A

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Speaker 1: few influential mathematicians and writers in the Middle East published

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Speaker 1: their thoughts on what was going on, and they got

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Speaker 1: the basics pretty much right. So what is going on? Well,

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Speaker 1: we have to remember that vision is all about light,

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Speaker 1: our perception of light. We see stuff because light from

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Speaker 1: some source has reflected off of stuff. The light passes

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Speaker 1: through the lens of our eyes, and the lens directs

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Speaker 1: light to the retina. You can think of the lens

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Speaker 1: as a method of bending light toward a point. In

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Speaker 1: this case, the lens of our eyes bends light so

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Speaker 1: that it hits our retina, which in turn then sends

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Speaker 1: signals to our brains, and that interprets the information it

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Speaker 1: receives in such a way that we experience vision. So

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Speaker 1: what we see is a filtered representation of what is

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Speaker 1: actually out there according to the light that we're able

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Speaker 1: to perceive. There's stuff well outside the visible spectrum. You know,

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Speaker 1: there's infrared light, there's ultraviolet light, and then beyond that's

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Speaker 1: out there too, but we can't see it without the

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Speaker 1: aid of technology. And even when we do use technology,

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Speaker 1: what we're really looking at is a conversion of those

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Speaker 1: types of light into something we can actually perceive within

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Speaker 1: the visible spectrum. A lens is a transparent material with

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Speaker 1: at least one curved surface, and the curved surface redirects light.

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Speaker 1: This is called refraction. The lens bends the light rays

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Speaker 1: and changes the direction of travel. So in a vacuum,

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Speaker 1: light will travel in a straight line, but the path

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Speaker 1: of light changes as it moves through different materials, particularly

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Speaker 1: as it transitions from one material to another. So when

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Speaker 1: we talk about the speed of light, we typically are

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Speaker 1: talking about light as it travels through a vacuum, because

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Speaker 1: then the speed of light is consistent, it does not

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Speaker 1: change it, and it's also the fastest stuff that we

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Speaker 1: know about in the universe. So when light moves through

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Speaker 1: a different material, transparent material, it slows down a bit

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Speaker 1: compared to how fast it travels through a vacuum. So

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Speaker 1: we can divide n is into two very broad categories,

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Speaker 1: convex lenses and concave lenses. A convex or positive lens

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Speaker 1: bulges outward. This causes incoming rays of light to converge

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Speaker 1: on one another, concentrating on a focal point behind the lens.

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Speaker 1: So you could use stuff like this to concentrate light

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Speaker 1: into a point and then use that to start a fire,

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Speaker 1: for example with a magnifying glass. Telescopes also use these

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Speaker 1: sort of lenses as their object lens. Will talk about

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Speaker 1: that in a second, so or objective lens. I should say, So,

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Speaker 1: if you think of this in a in a sense

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Speaker 1: of an illustration, and you have a convex lens, remember

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Speaker 1: it bulges out on either side. In this simple example,

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Speaker 1: you would have parallel rays of light coming in from

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Speaker 1: the outside hitting that convex lens, and then they would

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Speaker 1: all start to tilt inwards of each other, converging to

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Speaker 1: a point further out from that lens. And the point

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Speaker 1: where they actually do converge is the focal point for

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Speaker 1: that lens. We'll get back to that. Then you've got

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Speaker 1: concave or diverging lenses. The surface of a concave lens

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Speaker 1: bends inward. It's like a bowl, it bends inside. So

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Speaker 1: when parallel rays of light hit a concave lens, of

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Speaker 1: lights coming from outside traveling in those straight lines hits

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Speaker 1: the concave lens, they then bend away from each other.

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Speaker 1: They move further out from each other. So a projector

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Speaker 1: might use a concave lens to spread rays out across

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Speaker 1: a larger surface, like a movie screen. Now that's not

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Speaker 1: to say all lenses are either convex or concave. You

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Speaker 1: can make lenses with elements of each or other parts

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Speaker 1: that These are called compound lenses. So it can get

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Speaker 1: pretty complicated. But we're gonna really focus on there. It

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Speaker 1: is again focus We're gonna focus on the simpler versions. Now.

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Speaker 1: Early lenses like the Nimrod lens were made from quartz

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Speaker 1: crystal and ground down and polished to create a magnification effect.

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Speaker 1: This effect was not particularly strong, but it did show

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Speaker 1: that it was possible to manufacture refracting lenses. This led

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Speaker 1: to more research and hypothesizing. In the eleventh century, Arabic

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Speaker 1: scholars were writing about the early signs of optics, carrying

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Speaker 1: on the tradition begun by the Greek and Roman philosophers.

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Speaker 1: By the thirteenth century Italian inventors had figured out how

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Speaker 1: to grind lenses suitable for use as spectacles. Now, these

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Speaker 1: were essentially a pair of magnifying glasses that one would

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Speaker 1: wear a hold up to your eyes. And there were

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Speaker 1: a lot of different stories about who invented eyeglasses, though

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Speaker 1: many of these lack any substantiating evidence, and a few

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Speaker 1: have been uncovered as being outright hoaxes. Why is that, well,

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Speaker 1: because often it's a matter of local pride to lay

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Speaker 1: claim to an inventor of a transformative technology, and then

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Speaker 1: you can so that, oh, your village or town, or

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Speaker 1: city or country was their home, and therefore you are

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Speaker 1: all elevated in relation to that. Something that surprised me

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Speaker 1: when I looked into all this was that inventors created

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Speaker 1: the microscope before they created the telescope. I had always

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Speaker 1: assumed the opposite was true. Hans Libacy, whom I mentioned

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Speaker 1: earlier as the person most people credit as the quote

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Speaker 1: unquote inventor of the telescope, may also have invented the microscope,

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Speaker 1: but others say that honor should go to Hans and

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Speaker 1: Zacharias Jansen. They were a father son team of spectacle

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Speaker 1: makers who happened to live in the very same town

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Speaker 1: as Liberacy. So whomever invented the darned thing appears to

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Speaker 1: have been living in Holland, specifically in Middleburg. I guess

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Speaker 1: stuff was always sort of fuzzy there and they just

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Speaker 1: really needed a closer look whomever was responsible. The earliest

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Speaker 1: records we have for a microscope date back to the

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Speaker 1: fteen nineties. The microscope used a pair or sometimes more,

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Speaker 1: of magnifying lenses, and they weren't super powerful microscopes. They

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Speaker 1: were only capable of around three to nine times magnification.

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Speaker 1: Skipping ahead a few decades to Liberty in his patent application,

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Speaker 1: at least one version of his story involves him discovering

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Speaker 1: the potential for a telescope essentially by chance. Supposedly, according

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Speaker 1: to the story, Lipper she got an order from a

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Speaker 1: customer to make two lenses. One lens was going to

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Speaker 1: be convex, thus a convergent and magnifying lens. The other

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Speaker 1: was to be slightly concave or divergent. So he makes

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Speaker 1: the two lenses as requested, and the customer comes in,

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Speaker 1: picks up the two lenses, holds one of them close

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Speaker 1: to his eye, one further away from his eye and

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Speaker 1: looks through them, and then happily pays for the order

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Speaker 1: and leaves. Then, according to this story Lippor, she decides,

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Speaker 1: what the heck was that about? I gotta make a

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Speaker 1: pair of lenses to find out why that was what

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Speaker 1: does that mean? So he goes. He makes essentially a

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Speaker 1: copy of what he had already made for this customer,

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Speaker 1: just to see what the heck this is all about,

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Speaker 1: holds up the concave lens close to his eye the

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Speaker 1: convex lens further away, and then is astonished to find

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Speaker 1: out that through this combination he's able to view an

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Speaker 1: image of a church across town as if it were

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Speaker 1: right in front of him. It has magnified the image significantly,

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Speaker 1: and thus, according to this possibly apocryphal story, the telescope

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Speaker 1: was born. He sent a notice to the States General

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Speaker 1: of the Netherlands for this patent, and it would have

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Speaker 1: extended a patent for thirty years. He actually offered up

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Speaker 1: a couple of different options. He said, well, if you

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Speaker 1: don't want to do that, you could give me an

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Speaker 1: annual pension from the government, and in return, if you

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Speaker 1: do this, I'll promise I will not sell this telescope

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Speaker 1: invention to foreign powers, and thus the Netherlands will have

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Speaker 1: a superiority in that regard. Uh Zachary Jensen, the aforementioned

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Speaker 1: son in that father son duo that worked on the microscope,

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Speaker 1: would claim that he invented the telescope. And there was

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Speaker 1: a third inventor, Jacob Matthias, who disputed Liberty's claim as

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Speaker 1: inventor as well. So ultimately the government of the Netherlands said,

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Speaker 1: we can't give anyone a patent on this. It's widely

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Speaker 1: known already people are already making these, so there's no

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Speaker 1: way of knowing who owns the rights to this. However,

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Speaker 1: they did give Liberty and a reward of nine hundred florins,

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Speaker 1: which I am told is indeed a princely some in

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Speaker 1: those days. When I come back, I'll explain more about

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Speaker 1: the physics of light within a simple telescope before we

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Speaker 1: continue our journey towards how modern telescopes work today. But

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Speaker 1: first let's take a quick break. Now, one thing I

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Speaker 1: didn't really cover in that first section of the podcast

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Speaker 1: is why the heck do we need telescopes? I mean,

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Speaker 1: what is it about our vision that has this limiting

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Speaker 1: factor in the first place. Why are smaller objects or

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Speaker 1: objects that are much further away or both, why are

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Speaker 1: they hard to see? Well, remember when I said that

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Speaker 1: when we see something, what's actually happening is that the

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Speaker 1: lens of our eye is directing light reflected off that

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Speaker 1: object and sending it to our retina. Well, you can

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Speaker 1: think of the retina as being kind of like a sensor,

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Speaker 1: and it's picking up that light, and smaller objects or

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Speaker 1: stuff that's further away take up less space on that sensor,

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Speaker 1: So that's part of it. It's just it's it's taking

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Speaker 1: up a tinier amount of space on the retina, so

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Speaker 1: we're getting less information to our brains. Also, our eyes

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Speaker 1: are gathering lots of light reflected off of lots of surfaces,

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Speaker 1: and the light coming from a small, distant object can

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Speaker 1: be dwarfed by the light coming from everything else, and

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Speaker 1: eventually the object is too small or too far away

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Speaker 1: for any light reflected off of it to be read,

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Speaker 1: just stirred by our retinas. It's not that the light

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Speaker 1: isn't getting to us, but it's so small compared to

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Speaker 1: everything else that we can't register it. We can't recognize it,

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Speaker 1: so to see it more clearly, we would need a

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Speaker 1: lens that could take the light reflected off that object

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Speaker 1: and then spread that light across more of the surface

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Speaker 1: of the retina, and telescopes do that. And there are

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Speaker 1: a couple of different ways we can achieve this with

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Speaker 1: optical telescopes. One is through the lenses I've mentioned already,

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Speaker 1: that would be called a refracting telescope, and the other

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Speaker 1: is through mirrors, which will get too later, and those

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Speaker 1: are reflecting telescopes. So let's start off with refracting telescopes.

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Speaker 1: A simple refracting telescope uses a pair of lenses, like

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Speaker 1: what Lipacy discovered back in six eight. The objective lens

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Speaker 1: collects light from distant objects to a point of focus

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Speaker 1: that's within the telescope itself. So again, now imagine you've

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Speaker 1: got a lens at the end of a tube and

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Speaker 1: the peril rays are coming in and they hit this

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Speaker 1: this convex lens, the objective lens, and because it's a

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Speaker 1: convex lens, it bends the lights. So now the rays

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Speaker 1: are now converging into the tube to a focal point,

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Speaker 1: so they're bending inwards with relation to the tube within

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Speaker 1: the body of the telescope. Itself. Uh. Now with a

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Speaker 1: modern day telescope that's not a Galileean telescope, which I'll

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Speaker 1: get to in a second. Uh, those rays would hit

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Speaker 1: a focal point and they don't just stop. They're right.

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Speaker 1: It's not like the rays of light all converge into

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Speaker 1: a point of space and then just create a point

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Speaker 1: of light. Those rays will continue on in a straight line.

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Speaker 1: So now they're diverging from one another. They keep on

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Speaker 1: going until they hit something and they reflect off of it.

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Speaker 1: So the objective lens faces out into the world, and

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Speaker 1: the other lens is the eyepiece or ocular lens, and

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Speaker 1: that magnifies that light from within the telescope and spread

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Speaker 1: it out so that that light takes up more of

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Speaker 1: the space on your retina. So these diverging rays hit

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Speaker 1: that second lens. That second lens then bends the light

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Speaker 1: in a way that directs it towards the eye of

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Speaker 1: the person using the telescope in a in a parallel fashion,

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Speaker 1: So it returns the light to a parallel alignment. So

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Speaker 1: what you view through that eye piece is a virtual

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Speaker 1: representation of the real thing that the objective lens has

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Speaker 1: in focus. And this virtual object is much closer to

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Speaker 1: your eye than the real object is, so you get

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Speaker 1: the effective magnification lipatis. Early telescopes can magnify stuff to

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Speaker 1: about three times their relative size to the viewer's perspective,

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Speaker 1: so not incredible, but an improvement. One interesting point about

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Speaker 1: this type of telescope if we were talking specifically about

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Speaker 1: using convex lenses on both the objective lens and the

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Speaker 1: ocular lens, the eye piece lens or the optical lens,

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Speaker 1: if you prefer if you're using both of those as

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Speaker 1: convex lenses, and you're you've got the focal point inside

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Speaker 1: the telescope itself, the second lenses behind that focal point.

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Speaker 1: As the light converges and then diverges within the telescope,

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Speaker 1: the image flips upside down. So if you draw this out,

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Speaker 1: it all makes sense. The light rays are coming from

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Speaker 1: the outside world, right, and the light rays that are

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Speaker 1: on the top if you think of it in respect

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Speaker 1: of the telescope, the top of the telescope part, and

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Speaker 1: you're looking at a cross section of it, they get

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Speaker 1: bent so that they aimed downward relative to the telescope.

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Speaker 1: The light rays coming from the bottom side of the lens,

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Speaker 1: for example, then get bent upward with respect to the telescope,

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Speaker 1: and then they continue on their journey. They hit that

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Speaker 1: focal point and they keep going in a straight line. Uh.

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Speaker 1: And so the light that was at the bottom of

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Speaker 1: the objective lenses at the top of the optical lens

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Speaker 1: or the the ocular lens. The light that was the

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Speaker 1: top of the objective lens is at the bottom of

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Speaker 1: the I piece lens. So that's why if you were

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Speaker 1: looking through such a telescope, the object you were looking

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Speaker 1: at would be upside down. Uh. If we use such

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Speaker 1: a telescope to look at a celestial body, that's not

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Speaker 1: a big deal because top and bottom in space is

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Speaker 1: largely unimportant. If we wanted to use it in a

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Speaker 1: terrestrial sense, like you wanted to use the telescope to

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Speaker 1: look at stuff around you on Earth, Like let's say

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Speaker 1: that you have a spyglass and you're a pirate, then

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Speaker 1: looking at a distant object might be a bit of

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Speaker 1: a surprise because it would suddenly be flipped upside down.

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Speaker 1: Modern telescopes use stuff like prisms and mirrors to correct

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Speaker 1: for that vertical inversion. They're called erectors. But what about

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Speaker 1: old telescopes before we figured that out? We're all those

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Speaker 1: pirates we see in romanticized movies looking at stuff upside

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Speaker 1: down the whole time. Well no, so, while my description

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Speaker 1: of objective lenses and eyepieces and all that sort of

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Speaker 1: stuff is accurate. From modern refracting telescopes, the type used

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Speaker 1: by astronomers and seafarers from around oh say, sixteen ten

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Speaker 1: to about sixteen seventy or so followed the Galilean method.

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Speaker 1: Galileo began using telescopes for astronomical observations not long after

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Speaker 1: Liberacy's work became widely known. So like by six ten, Galileo,

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Speaker 1: like Libacy, used a convex lens as the objective lens,

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Speaker 1: and a concave or diverging or negative lens as the

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Speaker 1: eye piece lens. So like coming in through the objective

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Speaker 1: lens would bend inward towards a focal point, the diverging

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Speaker 1: lens would reverse the direction of the bend before the

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Speaker 1: rays could hit the user's eye, so the top and

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Speaker 1: bottom wouldn't switch, everything would still be in the proper alignment.

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Speaker 1: As the Institute and Museum of the History of Science

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Speaker 1: puts it, quote, the eye piece is situated in front

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Speaker 1: of the focal point of the objective at a distance

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Speaker 1: from the focal point equal to the focal length of

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Speaker 1: the eye piece end quote. That gets a little confusing,

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Speaker 1: but if you were to draw it out, it makes

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Speaker 1: a lot of sense. You would have the convex objective

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Speaker 1: lens at the front of the telescope. Lights coming from

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00:24:14,600 --> 00:24:18,359
Speaker 1: outside world in parallel rays. It hits that lens and

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Speaker 1: it bends inward, just as we've been talking about all

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Speaker 1: the way up through this podcast, they start to converge

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Speaker 1: on a focal point that's behind the lens. However, before

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Speaker 1: it gets to the point where all those rays have

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Speaker 1: converged into a single point of space, those rays hit

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Speaker 1: the eye piece lens, the concave lens, So instead of

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Speaker 1: all converging on a focal point, they first hit this

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Speaker 1: concave lens, which then bends the light again, and then

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Speaker 1: the concave lens causes the rays to diverge, returning to

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Speaker 1: a parallel arrangement. The The early inventors learned that there

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Speaker 1: was a precise art to getting the distance correct between

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Speaker 1: these two lenses. You couldn't just have them one in

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Speaker 1: front of the other and everything works out perfectly. To

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Speaker 1: really get it right, you needed to take the absolute

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Speaker 1: value of the focal length of each lens and then

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Speaker 1: calculate the difference between them. The difference represented the distance

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Speaker 1: between the two lenses you would need to produce the

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Speaker 1: magnification effect you wanted. So for a Galileean telescope, the

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Speaker 1: distance between the objective lens and the I piece or

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Speaker 1: optical lens is equal to the algebraic sum of the

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Speaker 1: two lenses focal lengths. That is, the distance between the

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Speaker 1: lens and its focal point. So concave lenses actually have

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Speaker 1: a negative focal point. The focal point of a concave

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Speaker 1: lens is in front of the lens, not behind the lens.

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Speaker 1: It's a little counterintuitive. So you add a positive value,

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Speaker 1: which is the convex lenses focal point. The focal point

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00:25:59,800 --> 00:26:02,520
Speaker 1: for a convex lens is behind it. Then you add

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Speaker 1: the negative value that's the concave lenses focal point, and

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00:26:06,560 --> 00:26:09,560
Speaker 1: then you get the difference essentially, because it would have

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Speaker 1: been the same as if you subtracted a positive sum

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Speaker 1: from another positive sum. The result is how far apart

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Speaker 1: those two lenses should be to produce the magnification effect. Now,

433
00:26:18,800 --> 00:26:22,160
Speaker 1: the amount of that magnification is also dependent upon the

434
00:26:22,200 --> 00:26:26,040
Speaker 1: focal length of the two lenses. Specifically, it depends upon

435
00:26:26,080 --> 00:26:29,719
Speaker 1: the ratio between the focal length of the objective lens

436
00:26:29,760 --> 00:26:31,920
Speaker 1: and then of the I piece lens. So you take

437
00:26:31,960 --> 00:26:35,199
Speaker 1: the objective lens focal length, you divide it by the

438
00:26:35,240 --> 00:26:39,040
Speaker 1: focal length of the optical lens. And later telescopes ones

439
00:26:39,080 --> 00:26:42,240
Speaker 1: that would use two convex lenses, rather than adding those

440
00:26:42,280 --> 00:26:44,840
Speaker 1: two focal lenks together, you would subtract the focal length

441
00:26:44,880 --> 00:26:46,840
Speaker 1: of the optical lens from the focal length of the

442
00:26:46,880 --> 00:26:50,119
Speaker 1: objective lens. Now, remember that in that case, the focal

443
00:26:50,200 --> 00:26:53,200
Speaker 1: length rh lens is a positive value. That's the only

444
00:26:53,240 --> 00:26:56,119
Speaker 1: reason that we had to add the two figures with

445
00:26:56,160 --> 00:26:59,560
Speaker 1: the Galilean telescope, because one of the values was negative.

446
00:27:00,160 --> 00:27:03,320
Speaker 1: The greater the diameter of the objective lens, the one

447
00:27:03,359 --> 00:27:06,159
Speaker 1: that's facing out to the world, the more light it

448
00:27:06,200 --> 00:27:09,800
Speaker 1: can collect. That seems pretty obvious, right. The bigger the lens,

449
00:27:09,840 --> 00:27:13,280
Speaker 1: the more light it's going to be able to redirect

450
00:27:13,400 --> 00:27:16,160
Speaker 1: inward to the telescope. By the way, the reason why

451
00:27:16,200 --> 00:27:19,560
Speaker 1: telescopes even have a tube there are a couple of reasons.

452
00:27:19,560 --> 00:27:23,359
Speaker 1: One is to keep out dust and other things that

453
00:27:23,400 --> 00:27:27,840
Speaker 1: could obscure the lenses, but another is it helps block

454
00:27:27,880 --> 00:27:30,840
Speaker 1: out any light that you don't want to come and

455
00:27:30,920 --> 00:27:33,240
Speaker 1: hit your eye. You want to really focus on whatever

456
00:27:33,400 --> 00:27:37,639
Speaker 1: object you're looking at. So the greater the diameter or

457
00:27:37,680 --> 00:27:41,520
Speaker 1: aperture of the objective, the more light it can collect.

458
00:27:41,800 --> 00:27:44,720
Speaker 1: Generally speaking, the more light it collects, the brighter the

459
00:27:44,800 --> 00:27:49,280
Speaker 1: distant image will actually be. And the greater the magnification

460
00:27:49,359 --> 00:27:53,000
Speaker 1: of your telescope, which again depends upon the relationship between

461
00:27:53,000 --> 00:27:55,840
Speaker 1: the focal length of lenses, the less field of view

462
00:27:56,000 --> 00:28:00,000
Speaker 1: you would end up having. So the objective lens die

463
00:28:00,040 --> 00:28:02,840
Speaker 1: ameter was what determines how much light comes in. It

464
00:28:02,920 --> 00:28:07,880
Speaker 1: does not necessarily determine how much magnification you get. That

465
00:28:08,000 --> 00:28:10,359
Speaker 1: is based more on the relationship between that lens and

466
00:28:10,359 --> 00:28:13,640
Speaker 1: the I piece lens. But then the amount of magnification

467
00:28:13,680 --> 00:28:16,400
Speaker 1: you get determines how much field of view you have.

468
00:28:16,880 --> 00:28:19,159
Speaker 1: If it's a greater amount of magnification, you're going to

469
00:28:19,280 --> 00:28:22,080
Speaker 1: see less of the night sky in the view of

470
00:28:22,080 --> 00:28:26,480
Speaker 1: your telescope. Now, there are practical limits that you hit

471
00:28:27,000 --> 00:28:31,440
Speaker 1: using lenses, because the bigger the lens, the more light

472
00:28:31,480 --> 00:28:34,040
Speaker 1: it can collect. But it also means that those lens

473
00:28:34,119 --> 00:28:37,960
Speaker 1: lenses have have more mass. That means the telescopes themselves

474
00:28:38,000 --> 00:28:41,600
Speaker 1: get heavier as a result. Moreover, if a lens is

475
00:28:41,640 --> 00:28:45,440
Speaker 1: too heavy, the weight can actually affect the shape of

476
00:28:45,480 --> 00:28:48,480
Speaker 1: the lens. It can warp it. And since the lens

477
00:28:48,520 --> 00:28:51,640
Speaker 1: shape determines where the light is going to go, that's

478
00:28:51,680 --> 00:28:53,920
Speaker 1: a bad thing. If you've designed a lens to direct

479
00:28:54,000 --> 00:28:56,800
Speaker 1: light in a very specific way, and then the lens

480
00:28:56,840 --> 00:28:59,280
Speaker 1: warps under its own weight, the light's not gonna go

481
00:28:59,360 --> 00:29:02,040
Speaker 1: where you plan, and so you start to reach practical

482
00:29:02,080 --> 00:29:05,720
Speaker 1: limits of what you can do using refracting telescopes. The

483
00:29:05,840 --> 00:29:10,200
Speaker 1: largest refracting telescope objective lens that's still in use today

484
00:29:10,440 --> 00:29:14,880
Speaker 1: is installed at the Yorkey's Observatory in Wisconsin. The lens

485
00:29:14,920 --> 00:29:18,920
Speaker 1: on that telescope measures one meter across or or a

486
00:29:18,920 --> 00:29:22,320
Speaker 1: little more than three feet. In other words, it weighs

487
00:29:22,360 --> 00:29:26,760
Speaker 1: around twenty six tons. That's how heavy glass gets when

488
00:29:26,800 --> 00:29:29,400
Speaker 1: you're looking at this, because remember it's a convex lens,

489
00:29:29,400 --> 00:29:31,240
Speaker 1: it bulges out. So it's not just that it's a

490
00:29:31,240 --> 00:29:35,000
Speaker 1: flat sheet of glass. It's not flat, it's it's curved.

491
00:29:35,560 --> 00:29:38,720
Speaker 1: So this is obviously a little heavier than what you

492
00:29:38,720 --> 00:29:42,360
Speaker 1: would use in the backyard telescope also I said still

493
00:29:42,400 --> 00:29:45,520
Speaker 1: in use, but technically the Yerkeys Observatory has been closed

494
00:29:45,520 --> 00:29:47,720
Speaker 1: to the public since the spring of two thousand eighteen,

495
00:29:48,040 --> 00:29:50,840
Speaker 1: when the University of Chicago announced it was seeking a

496
00:29:50,960 --> 00:29:54,880
Speaker 1: party to purchase this observatory and telescope and essentially take

497
00:29:54,920 --> 00:29:57,760
Speaker 1: it off university hands, which has not yet happened as

498
00:29:57,840 --> 00:30:01,480
Speaker 1: the recording of this episode. An other practical limitation of

499
00:30:01,520 --> 00:30:04,800
Speaker 1: refracting telescopes is that the lens must be in really

500
00:30:04,840 --> 00:30:09,440
Speaker 1: good shape right, so scratches, smudges, dust, all that can

501
00:30:09,480 --> 00:30:11,680
Speaker 1: make it difficult for light to pass through the lens.

502
00:30:12,120 --> 00:30:15,680
Speaker 1: And there's also the issue with lost light. Some of

503
00:30:15,680 --> 00:30:19,240
Speaker 1: the light hitting the lens doesn't pass through the lens,

504
00:30:19,280 --> 00:30:22,120
Speaker 1: it will reflect off the lens, and we see this

505
00:30:22,200 --> 00:30:25,000
Speaker 1: in our daily lives. If you look at a window

506
00:30:25,120 --> 00:30:27,880
Speaker 1: and you see your reflection and the window is transparent,

507
00:30:28,280 --> 00:30:31,000
Speaker 1: then that reflection is proof that some of the light

508
00:30:31,080 --> 00:30:34,880
Speaker 1: hitting that window is not passing through the glass. Instead

509
00:30:34,920 --> 00:30:37,640
Speaker 1: it's bouncing off the glass. The same thing is true

510
00:30:37,680 --> 00:30:40,240
Speaker 1: for telescope lenses, and the thicker and larger the lens,

511
00:30:40,280 --> 00:30:43,240
Speaker 1: the more light is going to be lost due to reflection.

512
00:30:44,000 --> 00:30:48,440
Speaker 1: Another limitation is called chromatic aberration, which sounds like a

513
00:30:48,480 --> 00:30:51,440
Speaker 1: monster from Dungeons and Dragons. But this all has to

514
00:30:51,480 --> 00:30:53,200
Speaker 1: do with the fact that light is made up of

515
00:30:53,240 --> 00:30:57,440
Speaker 1: many wavelengths, which we perceive as different colors. Those different

516
00:30:57,440 --> 00:31:01,640
Speaker 1: wavelengths have different focal lengths. The focal length of blue

517
00:31:01,720 --> 00:31:05,040
Speaker 1: light is different than the focal length for red light,

518
00:31:05,520 --> 00:31:08,440
Speaker 1: and these two wavelengths are pretty far apart on the spectrum,

519
00:31:08,440 --> 00:31:11,880
Speaker 1: which I'm sure you remember if you remember Roy g BV. Now,

520
00:31:12,200 --> 00:31:15,720
Speaker 1: what this means to us using telescopes is that the

521
00:31:15,840 --> 00:31:19,440
Speaker 1: different colors of light will not quite line up when

522
00:31:19,480 --> 00:31:22,480
Speaker 1: creating the image of the thing we're trying to look at.

523
00:31:23,000 --> 00:31:26,080
Speaker 1: The effect isn't enormous, but it's enough to create a

524
00:31:26,080 --> 00:31:29,440
Speaker 1: fringe of color around images, sort of like a rainbow

525
00:31:29,520 --> 00:31:33,120
Speaker 1: halo effect almost. And adding in other lenses and various

526
00:31:33,120 --> 00:31:37,360
Speaker 1: combinations can correct for chromatic aberration. But adding more lenses

527
00:31:37,720 --> 00:31:42,480
Speaker 1: means telescopes get way more expensive, delicate, and heavy. There's

528
00:31:42,480 --> 00:31:45,600
Speaker 1: a different approach that doesn't rely on lenses at all,

529
00:31:45,920 --> 00:31:49,160
Speaker 1: and those are reflecting telescopes, and I'll explain more about

530
00:31:49,200 --> 00:31:59,600
Speaker 1: those in just a second. Before we figured out how

531
00:31:59,640 --> 00:32:02,960
Speaker 1: to you lots of combinations of lenses and prisms to

532
00:32:03,040 --> 00:32:07,480
Speaker 1: correct for a chromatic aberration and other limitations of refracting telescopes.

533
00:32:07,800 --> 00:32:09,920
Speaker 1: There was another smarty pants who came up with a

534
00:32:09,920 --> 00:32:13,400
Speaker 1: different solution. That smarty pants would be Sir Isaac Newton,

535
00:32:13,640 --> 00:32:18,480
Speaker 1: who when not dodging falling apples or inventing calculus. And yeah,

536
00:32:18,520 --> 00:32:21,240
Speaker 1: I know he wasn't the only one to invent calculus.

537
00:32:21,280 --> 00:32:24,080
Speaker 1: He was coming up with nifty ways to improve telescopes,

538
00:32:24,400 --> 00:32:28,680
Speaker 1: and he did this around the sixteen seventies. Newton's solution,

539
00:32:28,840 --> 00:32:32,920
Speaker 1: which had previously been suggested by folks like Galileo, was

540
00:32:33,000 --> 00:32:37,400
Speaker 1: to rely upon a curved mirror rather than a lens

541
00:32:37,480 --> 00:32:40,680
Speaker 1: to gather light. The mirror would sit at the base

542
00:32:41,000 --> 00:32:43,360
Speaker 1: of the telescope. So again, if you think of the

543
00:32:43,440 --> 00:32:47,040
Speaker 1: telescope as a tube, then the mirror would be at

544
00:32:47,080 --> 00:32:49,920
Speaker 1: the bottom of the tube. The top of the tube

545
00:32:50,040 --> 00:32:54,480
Speaker 1: would be open, open to the night sky. The curved mirror,

546
00:32:54,720 --> 00:32:58,720
Speaker 1: a parabolic mirror, would reflect light so that all the

547
00:32:58,880 --> 00:33:02,680
Speaker 1: parallel rays come into the telescope would hit the mirror

548
00:33:02,880 --> 00:33:07,320
Speaker 1: and then reflect off on a converging pathway. So similar

549
00:33:07,520 --> 00:33:10,320
Speaker 1: in execution. If you can think of it that way,

550
00:33:10,320 --> 00:33:13,320
Speaker 1: and maybe not execution. Similar in effect to how a

551
00:33:13,480 --> 00:33:17,000
Speaker 1: convex lens bends light to converge on a focal point,

552
00:33:17,320 --> 00:33:21,200
Speaker 1: the parabolic mirror would reflect light to converge on a

553
00:33:21,240 --> 00:33:26,320
Speaker 1: focal point inside the telescope. However, Newton mounted a second

554
00:33:26,320 --> 00:33:30,640
Speaker 1: mirror sitting just ahead of where the focal point would be,

555
00:33:30,720 --> 00:33:35,120
Speaker 1: so in between the parabolic mirror and that mirror's focal point.

556
00:33:35,920 --> 00:33:40,120
Speaker 1: This the secondary mirror would reflect light coming from the

557
00:33:40,200 --> 00:33:44,880
Speaker 1: objective mirror at around a ninety degree angle toward an eyepiece,

558
00:33:45,160 --> 00:33:49,160
Speaker 1: which would provide magnification of the virtual image produced there.

559
00:33:49,480 --> 00:33:52,120
Speaker 1: So the light coming in from the main mirror bounces

560
00:33:52,160 --> 00:33:56,040
Speaker 1: off a second mirror and then you can see that light. Otherwise,

561
00:33:56,800 --> 00:33:59,480
Speaker 1: the parabolic mirror would just reflect light back out of

562
00:33:59,560 --> 00:34:01,640
Speaker 1: the open into the telescope. That would do you no good.

563
00:34:01,640 --> 00:34:03,400
Speaker 1: The only way to look into it would be to

564
00:34:03,760 --> 00:34:06,160
Speaker 1: put your head in the telescope, and then you're blocking

565
00:34:06,160 --> 00:34:09,440
Speaker 1: the light that's coming into it. So the secondary mirror

566
00:34:09,520 --> 00:34:12,319
Speaker 1: was to redirect light so you could actually see what

567
00:34:12,800 --> 00:34:16,400
Speaker 1: this telescope was observing. So, instead of an objective lens

568
00:34:16,840 --> 00:34:20,839
Speaker 1: to capture and bend light, Newton's telescope had an objective

569
00:34:21,040 --> 00:34:25,280
Speaker 1: mirror like a refracting telescope, the amount of light captured

570
00:34:25,640 --> 00:34:29,520
Speaker 1: is dependent upon the size of the objective component, but

571
00:34:29,760 --> 00:34:33,200
Speaker 1: a mirror's thickness doesn't have to change as you increase

572
00:34:33,239 --> 00:34:36,640
Speaker 1: its diameter. It doesn't bulge out, so you can make

573
00:34:36,680 --> 00:34:41,480
Speaker 1: a really thin, really large parabolic mirror. By contrast, the

574
00:34:41,560 --> 00:34:45,400
Speaker 1: refracting lens would get thicker as you increase the diameter

575
00:34:45,520 --> 00:34:49,520
Speaker 1: in order to get the proper refracting properties. So the

576
00:34:49,600 --> 00:34:53,160
Speaker 1: switch to a reflecting mirror meant you could construct much

577
00:34:53,280 --> 00:34:57,440
Speaker 1: larger telescopes without having to worry about dealing with really heavy,

578
00:34:57,640 --> 00:35:02,520
Speaker 1: very delicate lenses. Even a really big reflecting telescope could

579
00:35:02,520 --> 00:35:05,600
Speaker 1: be mounted on a sturdy support structure and the mirror

580
00:35:05,640 --> 00:35:09,680
Speaker 1: would retain its parabolic shape compared to those glass lenses

581
00:35:09,719 --> 00:35:12,920
Speaker 1: that would eventually warp from the weight of the lens itself.

582
00:35:13,520 --> 00:35:16,799
Speaker 1: And because the light was bouncing off mirrors rather than

583
00:35:16,880 --> 00:35:21,840
Speaker 1: passing through lenses, Newton didn't have to worry about chromatic aberration. However,

584
00:35:22,400 --> 00:35:27,560
Speaker 1: reflecting telescopes had their own sets of limitations. Early on,

585
00:35:27,600 --> 00:35:31,279
Speaker 1: a big limitation was focal length. The reflecting telescopes were

586
00:35:31,280 --> 00:35:35,040
Speaker 1: limited having a relatively short focal length, and since focal

587
00:35:35,120 --> 00:35:38,960
Speaker 1: length is tied to magnification, that meant reflecting telescopes were

588
00:35:39,040 --> 00:35:42,040
Speaker 1: largely limited and how much magnification you could get out

589
00:35:42,040 --> 00:35:44,880
Speaker 1: of them. This would later be addressed with innovations and

590
00:35:44,920 --> 00:35:47,719
Speaker 1: telescope design, but it was a bit of a limitation

591
00:35:47,719 --> 00:35:50,440
Speaker 1: in Newton's time. Also, while the telescope has had a

592
00:35:50,480 --> 00:35:54,040
Speaker 1: relatively short focal point, they also had a relatively large

593
00:35:54,120 --> 00:35:55,800
Speaker 1: field of view, so you can see more of the

594
00:35:55,920 --> 00:35:59,040
Speaker 1: night sky in the view using a reflecting telescope than

595
00:35:59,080 --> 00:36:04,719
Speaker 1: a comparatively similar refracting telescope. Another small limitation was the

596
00:36:04,800 --> 00:36:08,520
Speaker 1: reflecting mirror mounted above the objective mirror, you know, the

597
00:36:08,520 --> 00:36:12,520
Speaker 1: one that's in between the objective mirror and its focal point. Well,

598
00:36:12,560 --> 00:36:14,879
Speaker 1: it would block a little bit of the light coming

599
00:36:14,920 --> 00:36:17,760
Speaker 1: into the telescope. It wouldn't block any of your view

600
00:36:18,160 --> 00:36:22,359
Speaker 1: because essentially every point of the mirror would have a

601
00:36:22,400 --> 00:36:27,239
Speaker 1: full version of the image that was coming into the telescope,

602
00:36:27,680 --> 00:36:30,120
Speaker 1: So you were getting a full view, but you were

603
00:36:30,160 --> 00:36:32,759
Speaker 1: blocking some of the light coming into the telescope, so

604
00:36:32,840 --> 00:36:36,040
Speaker 1: the image would be a little more dim than otherwise

605
00:36:36,080 --> 00:36:40,880
Speaker 1: would be. So the bigger this reflecting mirror was the

606
00:36:40,960 --> 00:36:43,160
Speaker 1: more light it would block, and the dem or the

607
00:36:43,320 --> 00:36:46,799
Speaker 1: resulting image would be. The curved mirror also meant that

608
00:36:46,880 --> 00:36:50,080
Speaker 1: objects along the perimeter of the field of view would

609
00:36:50,080 --> 00:36:54,839
Speaker 1: be slightly warped. So anything in the center of your

610
00:36:54,920 --> 00:36:58,239
Speaker 1: view would be pretty accurate, but the closer you got

611
00:36:58,320 --> 00:37:01,560
Speaker 1: to the edge of your you, the more warped it

612
00:37:01,600 --> 00:37:04,600
Speaker 1: would get, and you would get these elongated images. So

613
00:37:04,640 --> 00:37:06,799
Speaker 1: if you're looking at a star, it might look more

614
00:37:06,920 --> 00:37:10,440
Speaker 1: like a tear drop or a comment. So that was

615
00:37:10,480 --> 00:37:13,440
Speaker 1: a little bit of a of a setback, or at

616
00:37:13,480 --> 00:37:16,719
Speaker 1: least a drawback, I should say. So, yeah, these telescopes

617
00:37:16,760 --> 00:37:20,680
Speaker 1: can get pretty big. The biggest in operation right now

618
00:37:21,239 --> 00:37:25,480
Speaker 1: is the Grund telescope Eo Canarius in La Palma, Spain,

619
00:37:26,120 --> 00:37:30,440
Speaker 1: as a diameter of ten point four meters or thirty

620
00:37:30,480 --> 00:37:34,759
Speaker 1: four point two feet. Now, remember, the largest refracting telescope

621
00:37:34,840 --> 00:37:38,879
Speaker 1: has an objective lens diameter of one meter, So this

622
00:37:39,120 --> 00:37:44,200
Speaker 1: reflecting telescope has an objective mirror ten times that diameter.

623
00:37:45,080 --> 00:37:49,160
Speaker 1: That's huge. Now, the mirror is also not a single

624
00:37:49,239 --> 00:37:54,200
Speaker 1: unbroken surface. It's not one ten point four meter across mirror.

625
00:37:54,200 --> 00:37:57,799
Speaker 1: It's actually made up of thirty six hexagonal mirrors that

626
00:37:57,880 --> 00:38:00,680
Speaker 1: fit together snugly, kind of like a puzzle piece. But

627
00:38:00,800 --> 00:38:04,560
Speaker 1: there's an even larger reflecting telescope that's currently in development.

628
00:38:04,840 --> 00:38:11,320
Speaker 1: It's called the European Extremely Large Telescope. Seems pretty self explanatory.

629
00:38:11,360 --> 00:38:15,000
Speaker 1: It's gonna have a reflecting objective mirror that measures approximately

630
00:38:15,200 --> 00:38:19,920
Speaker 1: forty meters in diameter, according to the European Southern Observatory.

631
00:38:20,160 --> 00:38:23,520
Speaker 1: The telescope will correct for atmospheric distortions, which is one

632
00:38:23,520 --> 00:38:26,319
Speaker 1: of the problems that we have just using telescopes here

633
00:38:26,360 --> 00:38:28,440
Speaker 1: on Earth. It's the fact that we have this pesky

634
00:38:28,640 --> 00:38:31,799
Speaker 1: atmosphere that gets in the way sometimes. Uh. The atmosphere

635
00:38:31,840 --> 00:38:34,279
Speaker 1: is why stars appear to twinkle when we look at them,

636
00:38:34,320 --> 00:38:36,680
Speaker 1: so that can be a problem when you're trying to

637
00:38:36,920 --> 00:38:41,120
Speaker 1: magnify all of that stuff. But this one's supposed to

638
00:38:41,120 --> 00:38:42,800
Speaker 1: correct for that. It's also supposed to be able to

639
00:38:42,840 --> 00:38:46,440
Speaker 1: collect thirteen times more light than any other optical telescope

640
00:38:46,440 --> 00:38:48,719
Speaker 1: we have here on Earth, and again, according to the

641
00:38:48,760 --> 00:38:52,319
Speaker 1: e s O, provide images that are sixteen times more

642
00:38:52,480 --> 00:38:55,799
Speaker 1: sharp than the Hubble Space telescope was able to. The

643
00:38:55,840 --> 00:38:58,600
Speaker 1: plan is to have this telescope ready to make observations

644
00:38:58,680 --> 00:39:02,560
Speaker 1: starting in twenty twenty five. Speaking of the Hubble, it

645
00:39:02,760 --> 00:39:06,200
Speaker 1: is itself a reflecting telescope. Specifically, it's a type of

646
00:39:06,280 --> 00:39:10,960
Speaker 1: reflecting telescope called a Cassegrain reflector, which uses a pair

647
00:39:11,040 --> 00:39:15,719
Speaker 1: of curved mirrors. The objective mirror is that concave parabolic

648
00:39:15,800 --> 00:39:18,520
Speaker 1: mirror design that I talked about just a moment ago,

649
00:39:18,920 --> 00:39:22,080
Speaker 1: but mounted above that, instead of a mirror that reflects

650
00:39:22,120 --> 00:39:25,840
Speaker 1: that image ninety degrees, it's actually a mirror facing the

651
00:39:25,920 --> 00:39:29,360
Speaker 1: first one, and this one is a convex mirror, so

652
00:39:29,400 --> 00:39:34,480
Speaker 1: it bulges outward, not curves inward. The parabolic mirror reflects

653
00:39:34,520 --> 00:39:38,600
Speaker 1: incoming light toward a focal point, and mounted ahead of

654
00:39:38,640 --> 00:39:41,800
Speaker 1: that focal point is this convex mirror, which then reflects

655
00:39:41,880 --> 00:39:45,919
Speaker 1: light back down the telescope in a converging point, and

656
00:39:46,080 --> 00:39:49,200
Speaker 1: the main parabolic mirror at the base of the telescope

657
00:39:49,239 --> 00:39:52,279
Speaker 1: has a small hole in the center that allows light

658
00:39:52,320 --> 00:39:54,960
Speaker 1: to pass through. The idea for the Hubble and other

659
00:39:55,040 --> 00:39:58,680
Speaker 1: space telescopes was that by putting telescopes in orbit and

660
00:39:58,719 --> 00:40:01,200
Speaker 1: thus outside of our atmosp fear, we could get an

661
00:40:01,280 --> 00:40:05,080
Speaker 1: unimpeded look at distant celestial bodies. You wouldn't have to

662
00:40:05,120 --> 00:40:10,840
Speaker 1: worry about atmospheric distortion or light pollution from terrestrial sources. Unfortunately,

663
00:40:11,280 --> 00:40:15,080
Speaker 1: after the Hubble Telescope had already launched into orbit, it

664
00:40:15,160 --> 00:40:20,080
Speaker 1: became clear that the objective mirror wasn't shaped correctly. It

665
00:40:20,200 --> 00:40:23,920
Speaker 1: was just slightly too flat by the order of a

666
00:40:23,960 --> 00:40:27,919
Speaker 1: couple of micrometers, so a very small error, but enough

667
00:40:27,960 --> 00:40:32,360
Speaker 1: to be catastrophic. That was enough to introduce spherical aberration,

668
00:40:32,520 --> 00:40:34,920
Speaker 1: which translates to people like you and me, as the

669
00:40:34,960 --> 00:40:38,680
Speaker 1: telescope was returning fuzzy images and it was supposed to

670
00:40:38,760 --> 00:40:43,600
Speaker 1: be super sharp, gorgeous images of the the galaxies around us. Now.

671
00:40:43,640 --> 00:40:47,000
Speaker 1: Eventually astronomers were able to come up with a solution,

672
00:40:47,360 --> 00:40:50,000
Speaker 1: though it would mean sending astronauts back up to the

673
00:40:50,040 --> 00:40:53,240
Speaker 1: Hubble Space Telescope to install a couple of additional mirrors

674
00:40:53,280 --> 00:40:56,239
Speaker 1: to correct for that issue, and in the process they

675
00:40:56,280 --> 00:40:59,239
Speaker 1: had to also remove some of the instrumentation that was

676
00:40:59,280 --> 00:41:02,839
Speaker 1: intended to get there other types of cosmological data. This

677
00:41:02,920 --> 00:41:05,960
Speaker 1: is what we would call a very expensive boo boo.

678
00:41:06,800 --> 00:41:09,920
Speaker 1: The James Webb Space Telescope, which is scheduled to launch

679
00:41:09,960 --> 00:41:13,560
Speaker 1: in twenty one, is of a similar design, but we'll

680
00:41:13,560 --> 00:41:16,560
Speaker 1: be exploring the universe. By collecting infrared light, which is

681
00:41:16,680 --> 00:41:19,520
Speaker 1: outside the visible spectrum, it will look at light that

682
00:41:19,640 --> 00:41:23,800
Speaker 1: is four times fainter than what current telescopes can detect,

683
00:41:24,640 --> 00:41:28,160
Speaker 1: and that means it can detect light from very distant sources.

684
00:41:28,440 --> 00:41:31,520
Speaker 1: And in space, you can think of distance and time

685
00:41:31,719 --> 00:41:35,440
Speaker 1: as being very closely related because it takes time for

686
00:41:35,600 --> 00:41:39,319
Speaker 1: light to travel distances. Now, light moves wicked fast. It's

687
00:41:39,360 --> 00:41:41,319
Speaker 1: the fastest stuff in the universe as far as we

688
00:41:41,360 --> 00:41:44,200
Speaker 1: can tell, but even so, it still takes time to

689
00:41:44,239 --> 00:41:47,080
Speaker 1: get from point A to point B. So when we

690
00:41:47,120 --> 00:41:50,280
Speaker 1: look up at stars, the light we're seeing from stars

691
00:41:50,680 --> 00:41:53,960
Speaker 1: might have taken a journey that lasted millions of years,

692
00:41:54,080 --> 00:41:57,680
Speaker 1: so we're effectively looking into the long distant past of

693
00:41:57,719 --> 00:42:00,880
Speaker 1: those celestial bodies. We're not seeing the star as it

694
00:42:00,960 --> 00:42:03,680
Speaker 1: is today. We're seeing the star as it was when

695
00:42:03,719 --> 00:42:07,680
Speaker 1: that light left the star, possibly millions of years ago.

696
00:42:08,000 --> 00:42:10,520
Speaker 1: And the James Webb is going to collect light from

697
00:42:10,600 --> 00:42:14,040
Speaker 1: further away than we've ever managed to do up to now,

698
00:42:14,400 --> 00:42:17,320
Speaker 1: meaning we'll be looking much further back into the past

699
00:42:17,480 --> 00:42:20,360
Speaker 1: of the universe than we've ever been capable of doing,

700
00:42:20,600 --> 00:42:24,040
Speaker 1: which is pretty darn cool. Now there's a lot I

701
00:42:24,080 --> 00:42:27,280
Speaker 1: didn't cover in this episode. For one thing, I stuck

702
00:42:27,320 --> 00:42:30,960
Speaker 1: with optical telescopes, but there are other kinds like radio telescopes.

703
00:42:31,280 --> 00:42:34,440
Speaker 1: For another, I didn't really talk about stuff like the erectors,

704
00:42:34,480 --> 00:42:36,839
Speaker 1: which are those devices that are meant to reverse that

705
00:42:36,960 --> 00:42:40,600
Speaker 1: vertical flipping thing that I talked about with refracting telescopes

706
00:42:40,880 --> 00:42:43,880
Speaker 1: if they're using two convex lenses. But I figured this

707
00:42:43,960 --> 00:42:46,719
Speaker 1: was a good overview into the super interesting piece of

708
00:42:46,719 --> 00:42:51,360
Speaker 1: technology that has at its heart very few components. But

709
00:42:51,480 --> 00:42:55,960
Speaker 1: those components have to be precisely designed, constructed, and placed

710
00:42:56,000 --> 00:42:59,840
Speaker 1: in relation to one another. So it's a real testament

711
00:42:59,840 --> 00:43:04,120
Speaker 1: to human ingenuity and also how sometimes the most impressive

712
00:43:04,160 --> 00:43:08,640
Speaker 1: technologies are not necessarily the most complicated when you get

713
00:43:08,640 --> 00:43:11,760
Speaker 1: down to it. If you guys have suggestions for future

714
00:43:11,840 --> 00:43:14,840
Speaker 1: episodes of tech Stuff, let me know. Send me an email.

715
00:43:14,880 --> 00:43:17,959
Speaker 1: The addresses tech Stuff at how stuparks dot com. Drop

716
00:43:18,000 --> 00:43:20,799
Speaker 1: on by our website that's text Stuff podcast dot com.

717
00:43:20,800 --> 00:43:23,480
Speaker 1: You're gonna find an archive of all of our past episodes.

718
00:43:23,800 --> 00:43:25,600
Speaker 1: You can do a search find out if the topic

719
00:43:25,680 --> 00:43:27,600
Speaker 1: you have in mind has already been covered. If not,

720
00:43:28,200 --> 00:43:30,080
Speaker 1: let me know. You can also find links to where

721
00:43:30,120 --> 00:43:32,960
Speaker 1: we are on social media in places like Twitter and Facebook.

722
00:43:32,960 --> 00:43:34,919
Speaker 1: Over there, so you can drop me a line there,

723
00:43:35,440 --> 00:43:37,319
Speaker 1: and don't forget. We also have a link to our

724
00:43:37,360 --> 00:43:39,799
Speaker 1: online store, where every purchase you make goes to help

725
00:43:39,880 --> 00:43:42,399
Speaker 1: the show, and we greatly appreciate it, and I'll talk

726
00:43:42,400 --> 00:43:50,120
Speaker 1: to you again really soon. Text Stuff is a production

727
00:43:50,160 --> 00:43:53,160
Speaker 1: of I Heart Radio's How Stuff Works. For more podcasts

728
00:43:53,200 --> 00:43:55,960
Speaker 1: from i heeart Radio, visit the I heart Radio app,

729
00:43:56,080 --> 00:43:59,240
Speaker 1: Apple Podcasts, or wherever you listen to your favorite shows.

730
00:44:01,080 --> 00:44:01,440
Speaker 1: Eight