Speaker 1: Welcome to tech Stuff, a production of I Heart Radios
Speaker 1: How Stuff Works. Hey there, and welcome to tech Stuff.
Speaker 1: I'm your host, Jonathan Strickland. I'm an executive producer with
Speaker 1: How Stuff Works in My Heart Radio and I love
Speaker 1: all things tech and way back in one a very
Speaker 1: not good film titled Robin Hood Prince of Thieves debut
Speaker 1: and don't at me. That movie is trash. I loved
Speaker 1: it as a kid, but it is garbage. It starred
Speaker 1: Kevin Costner as Robin of Locksley, better known as the
Speaker 1: outlaw Robin Hood, and the film is set in eleven
Speaker 1: ninety four and Robin had a lot of problems. The
Speaker 1: Sheriff Nottingham was on his back, his beloved made Marian
Speaker 1: gets kidnapped, and his accent kept going in and out,
Speaker 1: so you can imagine the stress he was under. But
Speaker 1: he also had some advance diages. Now, one of those
Speaker 1: was his ingenious companion a Zeem played by Morgan Freeman.
Speaker 1: And in one scene, a Zeem helps Robin get a
Speaker 1: better look at some adversaries using a telescope. Now that
Speaker 1: scene is meant to establish that a Zeem's homeland often
Speaker 1: viewed as a backward and savage place through the eyes
Speaker 1: of England, and by extension, the West in general is
Speaker 1: actually home to great learning and innovation. And that part
Speaker 1: was true. I mean, the Middle East has a long
Speaker 1: history of phenomenal achievements, but inventing a telescope in the
Speaker 1: late twelfth century is not among them. That was historically inaccurate,
Speaker 1: probably the least of the historical inaccuracies in that film.
Speaker 1: But still I wanted to start with this because this
Speaker 1: was just one of the many fictions and fallacies in
Speaker 1: The Robin Hood. But I figured it was a fun
Speaker 1: place to start off this episode about the telescope. We're
Speaker 1: gonna look at where it actually did come from and
Speaker 1: how basic telescopes were. I guess you could say it's
Speaker 1: the focus of this episode. H m hm. And So
Speaker 1: while I now will leave the film Robin Hood Prince
Speaker 1: of Thieves behind, just remember that everything I do, I
Speaker 1: do it for you. Now, As is the case with
Speaker 1: much of technology, it's not really possible for me to
Speaker 1: tell you who invented the first telescope. I can tell
Speaker 1: you that the person most folks credit with inventing the
Speaker 1: telescope was the German Dutch inventor Hans Lipperty. He applied
Speaker 1: for a patent for an invention he called the geiker
Speaker 1: or kaiker. It's kind of hard for me to pronounce
Speaker 1: because I don't speak Dutch, but it means looker in Dutch.
Speaker 1: We'll come back to it. For this invention to be
Speaker 1: possible at all, the first thing that has to happen
Speaker 1: is that humans needed to learn how to make glass.
Speaker 1: Now we don't have a record of that actually happened,
Speaker 1: but our best guess is that glassmaking became an actual
Speaker 1: thing around four thousand years ago in Mesa Potamia, as
Speaker 1: the B. Fifty two s would say, a region called Ptolemace,
Speaker 1: which is in now modern day Israel, was particularly known
Speaker 1: for this, having sand that was suitable for glassmaking, and
Speaker 1: early glassmakers would mix sand, soda, and lime which could
Speaker 1: then be heated in a furnace to create molten glass.
Speaker 1: To make a solid glass object, this mixture of sand, soda,
Speaker 1: and lime would first be put into an open mold,
Speaker 1: and the mold would be placed in the furnace, which
Speaker 1: would be heated up enough for the mixture to become
Speaker 1: molten glass. It would fill up this mold. They'd take
Speaker 1: the mold out and allow it to cool. Now, if
Speaker 1: you want to make a container something that could hold
Speaker 1: stuff like a vase or a perfume bottle, the glassmakers
Speaker 1: used a process called core forming. And yeah, I realized,
Speaker 1: I'm already getting a little far away from talking about
Speaker 1: telescopes and lenses. But I also think this process is
Speaker 1: super neat, so I want to explain it briefly. First,
Speaker 1: the glassmaker would determine what the interior shape of this
Speaker 1: object was going to be, so, for talking about a bottle,
Speaker 1: whether it's going to be tall and narrow, or whether
Speaker 1: it was going to be a wide jug, something along
Speaker 1: those lines. Then they would create the core out of
Speaker 1: a mixture of clay, sand, water, and uh poop or
Speaker 1: dung if you prefer, and then they would shape that
Speaker 1: into the rough form they wanted. Before they would insert
Speaker 1: a metal rod into one end of it, the essentially
Speaker 1: the end that would be in the open part of
Speaker 1: the container. They would then allow this core to dry.
Speaker 1: After it dried, the glassmaker would use tools to further
Speaker 1: refine the shape of the core, trimming it, filing it down,
Speaker 1: that kind of thing. Once finalized, Once it's in that
Speaker 1: final shape, the glassmaker would heat up a mixture of sand, lime,
Speaker 1: and soda in a crucible in a furnace, creating a
Speaker 1: molten glass inside that crucible. Then they would insert this
Speaker 1: core into that molten glass, hold down the metal rod.
Speaker 1: They would slowly twirl the core within the molten glass,
Speaker 1: getting a full coating on the core, sort of like
Speaker 1: coating a candy apple. The glassmaker would then remove this
Speaker 1: let cool a little bit, and use some other tools
Speaker 1: like pincers for example, to shape the glass while it
Speaker 1: was still a pliable and then after it had cooled
Speaker 1: down a bit, they might reheat it a little to
Speaker 1: to soften the glass, maybe add different colors of glass
Speaker 1: as decorations on top of it. You could twirl a
Speaker 1: line of molten glass on top of another layer, have
Speaker 1: contrasting colors and decorated that way. You might want to
Speaker 1: add things like handles to say a pot. Glassmakers would
Speaker 1: then change the color of the glass, by the way,
Speaker 1: by by mixing in metal oxides, because different metals would
Speaker 1: produce different colors. The whole process is super neat to watch.
Speaker 1: There's actually a lot of videos on YouTube about this process,
Speaker 1: so if it sounds interesting to you should really check
Speaker 1: it out because it's pretty neat to see how these
Speaker 1: ancient glassmakers would make this stuff. Anyway, glass was incredibly
Speaker 1: useful and it was much sought after, and these early
Speaker 1: examples I'm talking about we're really interesting. But the glass
Speaker 1: they produced were not at all suitable for creating any
Speaker 1: sort of lens. Those would have to wait for a
Speaker 1: couple of thousand years. But the foundation for it came
Speaker 1: from a pretty simple observation. Water has a magnifying effect,
Speaker 1: and humans in the ancient world noticed this and wondered,
Speaker 1: is there a way we could replicate this, where we
Speaker 1: could create a way to magnify stuff without having to
Speaker 1: use water. This led to ancient Egyptians and Mesopotamians experimenting
Speaker 1: with polished crystals, usually using courts around seven fifty b C.
Speaker 1: One such lens, the Nimrod lens, was made sometime around
Speaker 1: then in ancient Assyria. Smartie pants Greek and Roman philosophers
Speaker 1: began to hypothesize about what was actually going on with
Speaker 1: these materials, What was creating this magnification effect, how did
Speaker 1: it really how did it really work? They made some
Speaker 1: progress over the centuries and sussing things out, but the
Speaker 1: fall of the Roman Empire would set the world back
Speaker 1: more than a step or two. A lot of learning
Speaker 1: was lost, a lot of progress was halted. One place
Speaker 1: that continued the academic exploration of what was going on
Speaker 1: in the world of optics was in the Middle East,
Speaker 1: and this is probably where the Robin Hood crew got
Speaker 1: their idea for including a telescope in their screenplay. A
Speaker 1: few influential mathematicians and writers in the Middle East published
Speaker 1: their thoughts on what was going on, and they got
Speaker 1: the basics pretty much right. So what is going on? Well,
Speaker 1: we have to remember that vision is all about light,
Speaker 1: our perception of light. We see stuff because light from
Speaker 1: some source has reflected off of stuff. The light passes
Speaker 1: through the lens of our eyes, and the lens directs
Speaker 1: light to the retina. You can think of the lens
Speaker 1: as a method of bending light toward a point. In
Speaker 1: this case, the lens of our eyes bends light so
Speaker 1: that it hits our retina, which in turn then sends
Speaker 1: signals to our brains, and that interprets the information it
Speaker 1: receives in such a way that we experience vision. So
Speaker 1: what we see is a filtered representation of what is
Speaker 1: actually out there according to the light that we're able
Speaker 1: to perceive. There's stuff well outside the visible spectrum. You know,
Speaker 1: there's infrared light, there's ultraviolet light, and then beyond that's
Speaker 1: out there too, but we can't see it without the
Speaker 1: aid of technology. And even when we do use technology,
Speaker 1: what we're really looking at is a conversion of those
Speaker 1: types of light into something we can actually perceive within
Speaker 1: the visible spectrum. A lens is a transparent material with
Speaker 1: at least one curved surface, and the curved surface redirects light.
Speaker 1: This is called refraction. The lens bends the light rays
Speaker 1: and changes the direction of travel. So in a vacuum,
Speaker 1: light will travel in a straight line, but the path
Speaker 1: of light changes as it moves through different materials, particularly
Speaker 1: as it transitions from one material to another. So when
Speaker 1: we talk about the speed of light, we typically are
Speaker 1: talking about light as it travels through a vacuum, because
Speaker 1: then the speed of light is consistent, it does not
Speaker 1: change it, and it's also the fastest stuff that we
Speaker 1: know about in the universe. So when light moves through
Speaker 1: a different material, transparent material, it slows down a bit
Speaker 1: compared to how fast it travels through a vacuum. So
Speaker 1: we can divide n is into two very broad categories,
Speaker 1: convex lenses and concave lenses. A convex or positive lens
Speaker 1: bulges outward. This causes incoming rays of light to converge
Speaker 1: on one another, concentrating on a focal point behind the lens.
Speaker 1: So you could use stuff like this to concentrate light
Speaker 1: into a point and then use that to start a fire,
Speaker 1: for example with a magnifying glass. Telescopes also use these
Speaker 1: sort of lenses as their object lens. Will talk about
Speaker 1: that in a second, so or objective lens. I should say, So,
Speaker 1: if you think of this in a in a sense
Speaker 1: of an illustration, and you have a convex lens, remember
Speaker 1: it bulges out on either side. In this simple example,
Speaker 1: you would have parallel rays of light coming in from
Speaker 1: the outside hitting that convex lens, and then they would
Speaker 1: all start to tilt inwards of each other, converging to
Speaker 1: a point further out from that lens. And the point
Speaker 1: where they actually do converge is the focal point for
Speaker 1: that lens. We'll get back to that. Then you've got
Speaker 1: concave or diverging lenses. The surface of a concave lens
Speaker 1: bends inward. It's like a bowl, it bends inside. So
Speaker 1: when parallel rays of light hit a concave lens, of
Speaker 1: lights coming from outside traveling in those straight lines hits
Speaker 1: the concave lens, they then bend away from each other.
Speaker 1: They move further out from each other. So a projector
Speaker 1: might use a concave lens to spread rays out across
Speaker 1: a larger surface, like a movie screen. Now that's not
Speaker 1: to say all lenses are either convex or concave. You
Speaker 1: can make lenses with elements of each or other parts
Speaker 1: that These are called compound lenses. So it can get
Speaker 1: pretty complicated. But we're gonna really focus on there. It
Speaker 1: is again focus We're gonna focus on the simpler versions. Now.
Speaker 1: Early lenses like the Nimrod lens were made from quartz
Speaker 1: crystal and ground down and polished to create a magnification effect.
Speaker 1: This effect was not particularly strong, but it did show
Speaker 1: that it was possible to manufacture refracting lenses. This led
Speaker 1: to more research and hypothesizing. In the eleventh century, Arabic
Speaker 1: scholars were writing about the early signs of optics, carrying
Speaker 1: on the tradition begun by the Greek and Roman philosophers.
Speaker 1: By the thirteenth century Italian inventors had figured out how
Speaker 1: to grind lenses suitable for use as spectacles. Now, these
Speaker 1: were essentially a pair of magnifying glasses that one would
Speaker 1: wear a hold up to your eyes. And there were
Speaker 1: a lot of different stories about who invented eyeglasses, though
Speaker 1: many of these lack any substantiating evidence, and a few
Speaker 1: have been uncovered as being outright hoaxes. Why is that, well,
Speaker 1: because often it's a matter of local pride to lay
Speaker 1: claim to an inventor of a transformative technology, and then
Speaker 1: you can so that, oh, your village or town, or
Speaker 1: city or country was their home, and therefore you are
Speaker 1: all elevated in relation to that. Something that surprised me
Speaker 1: when I looked into all this was that inventors created
Speaker 1: the microscope before they created the telescope. I had always
Speaker 1: assumed the opposite was true. Hans Libacy, whom I mentioned
Speaker 1: earlier as the person most people credit as the quote
Speaker 1: unquote inventor of the telescope, may also have invented the microscope,
Speaker 1: but others say that honor should go to Hans and
Speaker 1: Zacharias Jansen. They were a father son team of spectacle
Speaker 1: makers who happened to live in the very same town
Speaker 1: as Liberacy. So whomever invented the darned thing appears to
Speaker 1: have been living in Holland, specifically in Middleburg. I guess
Speaker 1: stuff was always sort of fuzzy there and they just
Speaker 1: really needed a closer look whomever was responsible. The earliest
Speaker 1: records we have for a microscope date back to the
Speaker 1: fteen nineties. The microscope used a pair or sometimes more,
Speaker 1: of magnifying lenses, and they weren't super powerful microscopes. They
Speaker 1: were only capable of around three to nine times magnification.
Speaker 1: Skipping ahead a few decades to Liberty in his patent application,
Speaker 1: at least one version of his story involves him discovering
Speaker 1: the potential for a telescope essentially by chance. Supposedly, according
Speaker 1: to the story, Lipper she got an order from a
Speaker 1: customer to make two lenses. One lens was going to
Speaker 1: be convex, thus a convergent and magnifying lens. The other
Speaker 1: was to be slightly concave or divergent. So he makes
Speaker 1: the two lenses as requested, and the customer comes in,
Speaker 1: picks up the two lenses, holds one of them close
Speaker 1: to his eye, one further away from his eye and
Speaker 1: looks through them, and then happily pays for the order
Speaker 1: and leaves. Then, according to this story Lippor, she decides,
Speaker 1: what the heck was that about? I gotta make a
Speaker 1: pair of lenses to find out why that was what
Speaker 1: does that mean? So he goes. He makes essentially a
Speaker 1: copy of what he had already made for this customer,
Speaker 1: just to see what the heck this is all about,
Speaker 1: holds up the concave lens close to his eye the
Speaker 1: convex lens further away, and then is astonished to find
Speaker 1: out that through this combination he's able to view an
Speaker 1: image of a church across town as if it were
Speaker 1: right in front of him. It has magnified the image significantly,
Speaker 1: and thus, according to this possibly apocryphal story, the telescope
Speaker 1: was born. He sent a notice to the States General
Speaker 1: of the Netherlands for this patent, and it would have
Speaker 1: extended a patent for thirty years. He actually offered up
Speaker 1: a couple of different options. He said, well, if you
Speaker 1: don't want to do that, you could give me an
Speaker 1: annual pension from the government, and in return, if you
Speaker 1: do this, I'll promise I will not sell this telescope
Speaker 1: invention to foreign powers, and thus the Netherlands will have
Speaker 1: a superiority in that regard. Uh Zachary Jensen, the aforementioned
Speaker 1: son in that father son duo that worked on the microscope,
Speaker 1: would claim that he invented the telescope. And there was
Speaker 1: a third inventor, Jacob Matthias, who disputed Liberty's claim as
Speaker 1: inventor as well. So ultimately the government of the Netherlands said,
Speaker 1: we can't give anyone a patent on this. It's widely
Speaker 1: known already people are already making these, so there's no
Speaker 1: way of knowing who owns the rights to this. However,
Speaker 1: they did give Liberty and a reward of nine hundred florins,
Speaker 1: which I am told is indeed a princely some in
Speaker 1: those days. When I come back, I'll explain more about
Speaker 1: the physics of light within a simple telescope before we
Speaker 1: continue our journey towards how modern telescopes work today. But
Speaker 1: first let's take a quick break. Now, one thing I
Speaker 1: didn't really cover in that first section of the podcast
Speaker 1: is why the heck do we need telescopes? I mean,
Speaker 1: what is it about our vision that has this limiting
Speaker 1: factor in the first place. Why are smaller objects or
Speaker 1: objects that are much further away or both, why are
Speaker 1: they hard to see? Well, remember when I said that
Speaker 1: when we see something, what's actually happening is that the
Speaker 1: lens of our eye is directing light reflected off that
Speaker 1: object and sending it to our retina. Well, you can
Speaker 1: think of the retina as being kind of like a sensor,
Speaker 1: and it's picking up that light, and smaller objects or
Speaker 1: stuff that's further away take up less space on that sensor,
Speaker 1: So that's part of it. It's just it's it's taking
Speaker 1: up a tinier amount of space on the retina, so
Speaker 1: we're getting less information to our brains. Also, our eyes
Speaker 1: are gathering lots of light reflected off of lots of surfaces,
Speaker 1: and the light coming from a small, distant object can
Speaker 1: be dwarfed by the light coming from everything else, and
Speaker 1: eventually the object is too small or too far away
Speaker 1: for any light reflected off of it to be read,
Speaker 1: just stirred by our retinas. It's not that the light
Speaker 1: isn't getting to us, but it's so small compared to
Speaker 1: everything else that we can't register it. We can't recognize it,
Speaker 1: so to see it more clearly, we would need a
Speaker 1: lens that could take the light reflected off that object
Speaker 1: and then spread that light across more of the surface
Speaker 1: of the retina, and telescopes do that. And there are
Speaker 1: a couple of different ways we can achieve this with
Speaker 1: optical telescopes. One is through the lenses I've mentioned already,
Speaker 1: that would be called a refracting telescope, and the other
Speaker 1: is through mirrors, which will get too later, and those
Speaker 1: are reflecting telescopes. So let's start off with refracting telescopes.
Speaker 1: A simple refracting telescope uses a pair of lenses, like
Speaker 1: what Lipacy discovered back in six eight. The objective lens
Speaker 1: collects light from distant objects to a point of focus
Speaker 1: that's within the telescope itself. So again, now imagine you've
Speaker 1: got a lens at the end of a tube and
Speaker 1: the peril rays are coming in and they hit this
Speaker 1: this convex lens, the objective lens, and because it's a
Speaker 1: convex lens, it bends the lights. So now the rays
Speaker 1: are now converging into the tube to a focal point,
Speaker 1: so they're bending inwards with relation to the tube within
Speaker 1: the body of the telescope. Itself. Uh. Now with a
Speaker 1: modern day telescope that's not a Galileean telescope, which I'll
Speaker 1: get to in a second. Uh, those rays would hit
Speaker 1: a focal point and they don't just stop. They're right.
Speaker 1: It's not like the rays of light all converge into
Speaker 1: a point of space and then just create a point
Speaker 1: of light. Those rays will continue on in a straight line.
Speaker 1: So now they're diverging from one another. They keep on
Speaker 1: going until they hit something and they reflect off of it.
Speaker 1: So the objective lens faces out into the world, and
Speaker 1: the other lens is the eyepiece or ocular lens, and
Speaker 1: that magnifies that light from within the telescope and spread
Speaker 1: it out so that that light takes up more of
Speaker 1: the space on your retina. So these diverging rays hit
Speaker 1: that second lens. That second lens then bends the light
Speaker 1: in a way that directs it towards the eye of
Speaker 1: the person using the telescope in a in a parallel fashion,
Speaker 1: So it returns the light to a parallel alignment. So
Speaker 1: what you view through that eye piece is a virtual
Speaker 1: representation of the real thing that the objective lens has
Speaker 1: in focus. And this virtual object is much closer to
Speaker 1: your eye than the real object is, so you get
Speaker 1: the effective magnification lipatis. Early telescopes can magnify stuff to
Speaker 1: about three times their relative size to the viewer's perspective,
Speaker 1: so not incredible, but an improvement. One interesting point about
Speaker 1: this type of telescope if we were talking specifically about
Speaker 1: using convex lenses on both the objective lens and the
Speaker 1: ocular lens, the eye piece lens or the optical lens,
Speaker 1: if you prefer if you're using both of those as
Speaker 1: convex lenses, and you're you've got the focal point inside
Speaker 1: the telescope itself, the second lenses behind that focal point.
Speaker 1: As the light converges and then diverges within the telescope,
Speaker 1: the image flips upside down. So if you draw this out,
Speaker 1: it all makes sense. The light rays are coming from
Speaker 1: the outside world, right, and the light rays that are
Speaker 1: on the top if you think of it in respect
Speaker 1: of the telescope, the top of the telescope part, and
Speaker 1: you're looking at a cross section of it, they get
Speaker 1: bent so that they aimed downward relative to the telescope.
Speaker 1: The light rays coming from the bottom side of the lens,
Speaker 1: for example, then get bent upward with respect to the telescope,
Speaker 1: and then they continue on their journey. They hit that
Speaker 1: focal point and they keep going in a straight line. Uh.
Speaker 1: And so the light that was at the bottom of
Speaker 1: the objective lenses at the top of the optical lens
Speaker 1: or the the ocular lens. The light that was the
Speaker 1: top of the objective lens is at the bottom of
Speaker 1: the I piece lens. So that's why if you were
Speaker 1: looking through such a telescope, the object you were looking
Speaker 1: at would be upside down. Uh. If we use such
Speaker 1: a telescope to look at a celestial body, that's not
Speaker 1: a big deal because top and bottom in space is
Speaker 1: largely unimportant. If we wanted to use it in a
Speaker 1: terrestrial sense, like you wanted to use the telescope to
Speaker 1: look at stuff around you on Earth, Like let's say
Speaker 1: that you have a spyglass and you're a pirate, then
Speaker 1: looking at a distant object might be a bit of
Speaker 1: a surprise because it would suddenly be flipped upside down.
Speaker 1: Modern telescopes use stuff like prisms and mirrors to correct
Speaker 1: for that vertical inversion. They're called erectors. But what about
Speaker 1: old telescopes before we figured that out? We're all those
Speaker 1: pirates we see in romanticized movies looking at stuff upside
Speaker 1: down the whole time. Well no, so, while my description
Speaker 1: of objective lenses and eyepieces and all that sort of
Speaker 1: stuff is accurate. From modern refracting telescopes, the type used
Speaker 1: by astronomers and seafarers from around oh say, sixteen ten
Speaker 1: to about sixteen seventy or so followed the Galilean method.
Speaker 1: Galileo began using telescopes for astronomical observations not long after
Speaker 1: Liberacy's work became widely known. So like by six ten, Galileo,
Speaker 1: like Libacy, used a convex lens as the objective lens,
Speaker 1: and a concave or diverging or negative lens as the
Speaker 1: eye piece lens. So like coming in through the objective
Speaker 1: lens would bend inward towards a focal point, the diverging
Speaker 1: lens would reverse the direction of the bend before the
Speaker 1: rays could hit the user's eye, so the top and
Speaker 1: bottom wouldn't switch, everything would still be in the proper alignment.
Speaker 1: As the Institute and Museum of the History of Science
Speaker 1: puts it, quote, the eye piece is situated in front
Speaker 1: of the focal point of the objective at a distance
Speaker 1: from the focal point equal to the focal length of
Speaker 1: the eye piece end quote. That gets a little confusing,
Speaker 1: but if you were to draw it out, it makes
Speaker 1: a lot of sense. You would have the convex objective
Speaker 1: lens at the front of the telescope. Lights coming from
Speaker 1: outside world in parallel rays. It hits that lens and
Speaker 1: it bends inward, just as we've been talking about all
Speaker 1: the way up through this podcast, they start to converge
Speaker 1: on a focal point that's behind the lens. However, before
Speaker 1: it gets to the point where all those rays have
Speaker 1: converged into a single point of space, those rays hit
Speaker 1: the eye piece lens, the concave lens, So instead of
Speaker 1: all converging on a focal point, they first hit this
Speaker 1: concave lens, which then bends the light again, and then
Speaker 1: the concave lens causes the rays to diverge, returning to
Speaker 1: a parallel arrangement. The The early inventors learned that there
Speaker 1: was a precise art to getting the distance correct between
Speaker 1: these two lenses. You couldn't just have them one in
Speaker 1: front of the other and everything works out perfectly. To
Speaker 1: really get it right, you needed to take the absolute
Speaker 1: value of the focal length of each lens and then
Speaker 1: calculate the difference between them. The difference represented the distance
Speaker 1: between the two lenses you would need to produce the
Speaker 1: magnification effect you wanted. So for a Galileean telescope, the
Speaker 1: distance between the objective lens and the I piece or
Speaker 1: optical lens is equal to the algebraic sum of the
Speaker 1: two lenses focal lengths. That is, the distance between the
Speaker 1: lens and its focal point. So concave lenses actually have
Speaker 1: a negative focal point. The focal point of a concave
Speaker 1: lens is in front of the lens, not behind the lens.
Speaker 1: It's a little counterintuitive. So you add a positive value,
Speaker 1: which is the convex lenses focal point. The focal point
Speaker 1: for a convex lens is behind it. Then you add
Speaker 1: the negative value that's the concave lenses focal point, and
Speaker 1: then you get the difference essentially, because it would have
Speaker 1: been the same as if you subtracted a positive sum
Speaker 1: from another positive sum. The result is how far apart
Speaker 1: those two lenses should be to produce the magnification effect. Now,
Speaker 1: the amount of that magnification is also dependent upon the
Speaker 1: focal length of the two lenses. Specifically, it depends upon
Speaker 1: the ratio between the focal length of the objective lens
Speaker 1: and then of the I piece lens. So you take
Speaker 1: the objective lens focal length, you divide it by the
Speaker 1: focal length of the optical lens. And later telescopes ones
Speaker 1: that would use two convex lenses, rather than adding those
Speaker 1: two focal lenks together, you would subtract the focal length
Speaker 1: of the optical lens from the focal length of the
Speaker 1: objective lens. Now, remember that in that case, the focal
Speaker 1: length rh lens is a positive value. That's the only
Speaker 1: reason that we had to add the two figures with
Speaker 1: the Galilean telescope, because one of the values was negative.
Speaker 1: The greater the diameter of the objective lens, the one
Speaker 1: that's facing out to the world, the more light it
Speaker 1: can collect. That seems pretty obvious, right. The bigger the lens,
Speaker 1: the more light it's going to be able to redirect
Speaker 1: inward to the telescope. By the way, the reason why
Speaker 1: telescopes even have a tube there are a couple of reasons.
Speaker 1: One is to keep out dust and other things that
Speaker 1: could obscure the lenses, but another is it helps block
Speaker 1: out any light that you don't want to come and
Speaker 1: hit your eye. You want to really focus on whatever
Speaker 1: object you're looking at. So the greater the diameter or
Speaker 1: aperture of the objective, the more light it can collect.
Speaker 1: Generally speaking, the more light it collects, the brighter the
Speaker 1: distant image will actually be. And the greater the magnification
Speaker 1: of your telescope, which again depends upon the relationship between
Speaker 1: the focal length of lenses, the less field of view
Speaker 1: you would end up having. So the objective lens die
Speaker 1: ameter was what determines how much light comes in. It
Speaker 1: does not necessarily determine how much magnification you get. That
Speaker 1: is based more on the relationship between that lens and
Speaker 1: the I piece lens. But then the amount of magnification
Speaker 1: you get determines how much field of view you have.
Speaker 1: If it's a greater amount of magnification, you're going to
Speaker 1: see less of the night sky in the view of
Speaker 1: your telescope. Now, there are practical limits that you hit
Speaker 1: using lenses, because the bigger the lens, the more light
Speaker 1: it can collect. But it also means that those lens
Speaker 1: lenses have have more mass. That means the telescopes themselves
Speaker 1: get heavier as a result. Moreover, if a lens is
Speaker 1: too heavy, the weight can actually affect the shape of
Speaker 1: the lens. It can warp it. And since the lens
Speaker 1: shape determines where the light is going to go, that's
Speaker 1: a bad thing. If you've designed a lens to direct
Speaker 1: light in a very specific way, and then the lens
Speaker 1: warps under its own weight, the light's not gonna go
Speaker 1: where you plan, and so you start to reach practical
Speaker 1: limits of what you can do using refracting telescopes. The
Speaker 1: largest refracting telescope objective lens that's still in use today
Speaker 1: is installed at the Yorkey's Observatory in Wisconsin. The lens
Speaker 1: on that telescope measures one meter across or or a
Speaker 1: little more than three feet. In other words, it weighs
Speaker 1: around twenty six tons. That's how heavy glass gets when
Speaker 1: you're looking at this, because remember it's a convex lens,
Speaker 1: it bulges out. So it's not just that it's a
Speaker 1: flat sheet of glass. It's not flat, it's it's curved.
Speaker 1: So this is obviously a little heavier than what you
Speaker 1: would use in the backyard telescope also I said still
Speaker 1: in use, but technically the Yerkeys Observatory has been closed
Speaker 1: to the public since the spring of two thousand eighteen,
Speaker 1: when the University of Chicago announced it was seeking a
Speaker 1: party to purchase this observatory and telescope and essentially take
Speaker 1: it off university hands, which has not yet happened as
Speaker 1: the recording of this episode. An other practical limitation of
Speaker 1: refracting telescopes is that the lens must be in really
Speaker 1: good shape right, so scratches, smudges, dust, all that can
Speaker 1: make it difficult for light to pass through the lens.
Speaker 1: And there's also the issue with lost light. Some of
Speaker 1: the light hitting the lens doesn't pass through the lens,
Speaker 1: it will reflect off the lens, and we see this
Speaker 1: in our daily lives. If you look at a window
Speaker 1: and you see your reflection and the window is transparent,
Speaker 1: then that reflection is proof that some of the light
Speaker 1: hitting that window is not passing through the glass. Instead
Speaker 1: it's bouncing off the glass. The same thing is true
Speaker 1: for telescope lenses, and the thicker and larger the lens,
Speaker 1: the more light is going to be lost due to reflection.
Speaker 1: Another limitation is called chromatic aberration, which sounds like a
Speaker 1: monster from Dungeons and Dragons. But this all has to
Speaker 1: do with the fact that light is made up of
Speaker 1: many wavelengths, which we perceive as different colors. Those different
Speaker 1: wavelengths have different focal lengths. The focal length of blue
Speaker 1: light is different than the focal length for red light,
Speaker 1: and these two wavelengths are pretty far apart on the spectrum,
Speaker 1: which I'm sure you remember if you remember Roy g BV. Now,
Speaker 1: what this means to us using telescopes is that the
Speaker 1: different colors of light will not quite line up when
Speaker 1: creating the image of the thing we're trying to look at.
Speaker 1: The effect isn't enormous, but it's enough to create a
Speaker 1: fringe of color around images, sort of like a rainbow
Speaker 1: halo effect almost. And adding in other lenses and various
Speaker 1: combinations can correct for chromatic aberration. But adding more lenses
Speaker 1: means telescopes get way more expensive, delicate, and heavy. There's
Speaker 1: a different approach that doesn't rely on lenses at all,
Speaker 1: and those are reflecting telescopes, and I'll explain more about
Speaker 1: those in just a second. Before we figured out how
Speaker 1: to you lots of combinations of lenses and prisms to
Speaker 1: correct for a chromatic aberration and other limitations of refracting telescopes.
Speaker 1: There was another smarty pants who came up with a
Speaker 1: different solution. That smarty pants would be Sir Isaac Newton,
Speaker 1: who when not dodging falling apples or inventing calculus. And yeah,
Speaker 1: I know he wasn't the only one to invent calculus.
Speaker 1: He was coming up with nifty ways to improve telescopes,
Speaker 1: and he did this around the sixteen seventies. Newton's solution,
Speaker 1: which had previously been suggested by folks like Galileo, was
Speaker 1: to rely upon a curved mirror rather than a lens
Speaker 1: to gather light. The mirror would sit at the base
Speaker 1: of the telescope. So again, if you think of the
Speaker 1: telescope as a tube, then the mirror would be at
Speaker 1: the bottom of the tube. The top of the tube
Speaker 1: would be open, open to the night sky. The curved mirror,
Speaker 1: a parabolic mirror, would reflect light so that all the
Speaker 1: parallel rays come into the telescope would hit the mirror
Speaker 1: and then reflect off on a converging pathway. So similar
Speaker 1: in execution. If you can think of it that way,
Speaker 1: and maybe not execution. Similar in effect to how a
Speaker 1: convex lens bends light to converge on a focal point,
Speaker 1: the parabolic mirror would reflect light to converge on a
Speaker 1: focal point inside the telescope. However, Newton mounted a second
Speaker 1: mirror sitting just ahead of where the focal point would be,
Speaker 1: so in between the parabolic mirror and that mirror's focal point.
Speaker 1: This the secondary mirror would reflect light coming from the
Speaker 1: objective mirror at around a ninety degree angle toward an eyepiece,
Speaker 1: which would provide magnification of the virtual image produced there.
Speaker 1: So the light coming in from the main mirror bounces
Speaker 1: off a second mirror and then you can see that light. Otherwise,
Speaker 1: the parabolic mirror would just reflect light back out of
Speaker 1: the open into the telescope. That would do you no good.
Speaker 1: The only way to look into it would be to
Speaker 1: put your head in the telescope, and then you're blocking
Speaker 1: the light that's coming into it. So the secondary mirror
Speaker 1: was to redirect light so you could actually see what
Speaker 1: this telescope was observing. So, instead of an objective lens
Speaker 1: to capture and bend light, Newton's telescope had an objective
Speaker 1: mirror like a refracting telescope, the amount of light captured
Speaker 1: is dependent upon the size of the objective component, but
Speaker 1: a mirror's thickness doesn't have to change as you increase
Speaker 1: its diameter. It doesn't bulge out, so you can make
Speaker 1: a really thin, really large parabolic mirror. By contrast, the
Speaker 1: refracting lens would get thicker as you increase the diameter
Speaker 1: in order to get the proper refracting properties. So the
Speaker 1: switch to a reflecting mirror meant you could construct much
Speaker 1: larger telescopes without having to worry about dealing with really heavy,
Speaker 1: very delicate lenses. Even a really big reflecting telescope could
Speaker 1: be mounted on a sturdy support structure and the mirror
Speaker 1: would retain its parabolic shape compared to those glass lenses
Speaker 1: that would eventually warp from the weight of the lens itself.
Speaker 1: And because the light was bouncing off mirrors rather than
Speaker 1: passing through lenses, Newton didn't have to worry about chromatic aberration. However,
Speaker 1: reflecting telescopes had their own sets of limitations. Early on,
Speaker 1: a big limitation was focal length. The reflecting telescopes were
Speaker 1: limited having a relatively short focal length, and since focal
Speaker 1: length is tied to magnification, that meant reflecting telescopes were
Speaker 1: largely limited and how much magnification you could get out
Speaker 1: of them. This would later be addressed with innovations and
Speaker 1: telescope design, but it was a bit of a limitation
Speaker 1: in Newton's time. Also, while the telescope has had a
Speaker 1: relatively short focal point, they also had a relatively large
Speaker 1: field of view, so you can see more of the
Speaker 1: night sky in the view using a reflecting telescope than
Speaker 1: a comparatively similar refracting telescope. Another small limitation was the
Speaker 1: reflecting mirror mounted above the objective mirror, you know, the
Speaker 1: one that's in between the objective mirror and its focal point. Well,
Speaker 1: it would block a little bit of the light coming
Speaker 1: into the telescope. It wouldn't block any of your view
Speaker 1: because essentially every point of the mirror would have a
Speaker 1: full version of the image that was coming into the telescope,
Speaker 1: So you were getting a full view, but you were
Speaker 1: blocking some of the light coming into the telescope, so
Speaker 1: the image would be a little more dim than otherwise
Speaker 1: would be. So the bigger this reflecting mirror was the
Speaker 1: more light it would block, and the dem or the
Speaker 1: resulting image would be. The curved mirror also meant that
Speaker 1: objects along the perimeter of the field of view would
Speaker 1: be slightly warped. So anything in the center of your
Speaker 1: view would be pretty accurate, but the closer you got
Speaker 1: to the edge of your you, the more warped it
Speaker 1: would get, and you would get these elongated images. So
Speaker 1: if you're looking at a star, it might look more
Speaker 1: like a tear drop or a comment. So that was
Speaker 1: a little bit of a of a setback, or at
Speaker 1: least a drawback, I should say. So, yeah, these telescopes
Speaker 1: can get pretty big. The biggest in operation right now
Speaker 1: is the Grund telescope Eo Canarius in La Palma, Spain,
Speaker 1: as a diameter of ten point four meters or thirty
Speaker 1: four point two feet. Now, remember, the largest refracting telescope
Speaker 1: has an objective lens diameter of one meter, So this
Speaker 1: reflecting telescope has an objective mirror ten times that diameter.
Speaker 1: That's huge. Now, the mirror is also not a single
Speaker 1: unbroken surface. It's not one ten point four meter across mirror.
Speaker 1: It's actually made up of thirty six hexagonal mirrors that
Speaker 1: fit together snugly, kind of like a puzzle piece. But
Speaker 1: there's an even larger reflecting telescope that's currently in development.
Speaker 1: It's called the European Extremely Large Telescope. Seems pretty self explanatory.
Speaker 1: It's gonna have a reflecting objective mirror that measures approximately
Speaker 1: forty meters in diameter, according to the European Southern Observatory.
Speaker 1: The telescope will correct for atmospheric distortions, which is one
Speaker 1: of the problems that we have just using telescopes here
Speaker 1: on Earth. It's the fact that we have this pesky
Speaker 1: atmosphere that gets in the way sometimes. Uh. The atmosphere
Speaker 1: is why stars appear to twinkle when we look at them,
Speaker 1: so that can be a problem when you're trying to
Speaker 1: magnify all of that stuff. But this one's supposed to
Speaker 1: correct for that. It's also supposed to be able to
Speaker 1: collect thirteen times more light than any other optical telescope
Speaker 1: we have here on Earth, and again, according to the
Speaker 1: e s O, provide images that are sixteen times more
Speaker 1: sharp than the Hubble Space telescope was able to. The
Speaker 1: plan is to have this telescope ready to make observations
Speaker 1: starting in twenty twenty five. Speaking of the Hubble, it
Speaker 1: is itself a reflecting telescope. Specifically, it's a type of
Speaker 1: reflecting telescope called a Cassegrain reflector, which uses a pair
Speaker 1: of curved mirrors. The objective mirror is that concave parabolic
Speaker 1: mirror design that I talked about just a moment ago,
Speaker 1: but mounted above that, instead of a mirror that reflects
Speaker 1: that image ninety degrees, it's actually a mirror facing the
Speaker 1: first one, and this one is a convex mirror, so
Speaker 1: it bulges outward, not curves inward. The parabolic mirror reflects
Speaker 1: incoming light toward a focal point, and mounted ahead of
Speaker 1: that focal point is this convex mirror, which then reflects
Speaker 1: light back down the telescope in a converging point, and
Speaker 1: the main parabolic mirror at the base of the telescope
Speaker 1: has a small hole in the center that allows light
Speaker 1: to pass through. The idea for the Hubble and other
Speaker 1: space telescopes was that by putting telescopes in orbit and
Speaker 1: thus outside of our atmosp fear, we could get an
Speaker 1: unimpeded look at distant celestial bodies. You wouldn't have to
Speaker 1: worry about atmospheric distortion or light pollution from terrestrial sources. Unfortunately,
Speaker 1: after the Hubble Telescope had already launched into orbit, it
Speaker 1: became clear that the objective mirror wasn't shaped correctly. It
Speaker 1: was just slightly too flat by the order of a
Speaker 1: couple of micrometers, so a very small error, but enough
Speaker 1: to be catastrophic. That was enough to introduce spherical aberration,
Speaker 1: which translates to people like you and me, as the
Speaker 1: telescope was returning fuzzy images and it was supposed to
Speaker 1: be super sharp, gorgeous images of the the galaxies around us. Now.
Speaker 1: Eventually astronomers were able to come up with a solution,
Speaker 1: though it would mean sending astronauts back up to the
Speaker 1: Hubble Space Telescope to install a couple of additional mirrors
Speaker 1: to correct for that issue, and in the process they
Speaker 1: had to also remove some of the instrumentation that was
Speaker 1: intended to get there other types of cosmological data. This
Speaker 1: is what we would call a very expensive boo boo.
Speaker 1: The James Webb Space Telescope, which is scheduled to launch
Speaker 1: in twenty one, is of a similar design, but we'll
Speaker 1: be exploring the universe. By collecting infrared light, which is
Speaker 1: outside the visible spectrum, it will look at light that
Speaker 1: is four times fainter than what current telescopes can detect,
Speaker 1: and that means it can detect light from very distant sources.
Speaker 1: And in space, you can think of distance and time
Speaker 1: as being very closely related because it takes time for
Speaker 1: light to travel distances. Now, light moves wicked fast. It's
Speaker 1: the fastest stuff in the universe as far as we
Speaker 1: can tell, but even so, it still takes time to
Speaker 1: get from point A to point B. So when we
Speaker 1: look up at stars, the light we're seeing from stars
Speaker 1: might have taken a journey that lasted millions of years,
Speaker 1: so we're effectively looking into the long distant past of
Speaker 1: those celestial bodies. We're not seeing the star as it
Speaker 1: is today. We're seeing the star as it was when
Speaker 1: that light left the star, possibly millions of years ago.
Speaker 1: And the James Webb is going to collect light from
Speaker 1: further away than we've ever managed to do up to now,
Speaker 1: meaning we'll be looking much further back into the past
Speaker 1: of the universe than we've ever been capable of doing,
Speaker 1: which is pretty darn cool. Now there's a lot I
Speaker 1: didn't cover in this episode. For one thing, I stuck
Speaker 1: with optical telescopes, but there are other kinds like radio telescopes.
Speaker 1: For another, I didn't really talk about stuff like the erectors,
Speaker 1: which are those devices that are meant to reverse that
Speaker 1: vertical flipping thing that I talked about with refracting telescopes
Speaker 1: if they're using two convex lenses. But I figured this
Speaker 1: was a good overview into the super interesting piece of
Speaker 1: technology that has at its heart very few components. But
Speaker 1: those components have to be precisely designed, constructed, and placed
Speaker 1: in relation to one another. So it's a real testament
Speaker 1: to human ingenuity and also how sometimes the most impressive
Speaker 1: technologies are not necessarily the most complicated when you get
Speaker 1: down to it. If you guys have suggestions for future
Speaker 1: episodes of tech Stuff, let me know. Send me an email.
Speaker 1: The addresses tech Stuff at how stuparks dot com. Drop
Speaker 1: on by our website that's text Stuff podcast dot com.
Speaker 1: You're gonna find an archive of all of our past episodes.
Speaker 1: You can do a search find out if the topic
Speaker 1: you have in mind has already been covered. If not,
Speaker 1: let me know. You can also find links to where
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Speaker 1: Over there, so you can drop me a line there,
Speaker 1: and don't forget. We also have a link to our
Speaker 1: online store, where every purchase you make goes to help
Speaker 1: the show, and we greatly appreciate it, and I'll talk
Speaker 1: to you again really soon. Text Stuff is a production
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