TechStuff Looks through a Telescope

it as a kid, but it is garbage. It starred Kevin Costner as Robin of Locksley, better known as the outlaw Robin Hood, and the film is set in eleven ninety four and Robin had a lot of problems. The Sheriff Nottingham was on his back, his beloved made Marian gets kidnapped, and his accent kept going in and out, so you can imagine the stress he was under. But he also had some advance diages. Now, one of those was his ingenious companion a Zeem played by Morgan Freeman.

And in one scene, a Zeem helps Robin get a better look at some adversaries using a telescope. Now that scene is meant to establish that a Zeem's homeland often viewed as a backward and savage place through the eyes of England, and by extension, the West in general is actually home to great learning and innovation. And that part was true. I mean, the Middle East has a long history of phenomenal achievements, but inventing a telescope in the

late twelfth century is not among them. That was historically inaccurate, probably the least of the historical inaccuracies in that film. But still I wanted to start with this because this was just one of the many fictions and fallacies in The Robin Hood. But I figured it was a fun place to start off this episode about the telescope. We're gonna look at where it actually did come from and how basic telescopes were. I guess you could say it's

the focus of this episode. H m hm. And So while I now will leave the film Robin Hood Prince of Thieves behind, just remember that everything I do, I do it for you. Now, As is the case with much of technology, it's not really possible for me to tell you who invented the first telescope. I can tell you that the person most folks credit with inventing the telescope was the German Dutch inventor Hans Lipperty. He applied for a patent for an invention he called the geiker

or kaiker. It's kind of hard for me to pronounce because I don't speak Dutch, but it means looker in Dutch. We'll come back to it. For this invention to be possible at all, the first thing that has to happen is that humans needed to learn how to make glass.

Now we don't have a record of that actually happened, but our best guess is that glassmaking became an actual thing around four thousand years ago in Mesa Potamia, as the B. Fifty two s would say, a region called Ptolemace, which is in now modern day Israel, was particularly known for this, having sand that was suitable for glassmaking, and early glassmakers would mix sand, soda, and lime which could then be heated in a furnace to create molten glass.

To make a solid glass object, this mixture of sand, soda, and lime would first be put into an open mold, and the mold would be placed in the furnace, which would be heated up enough for the mixture to become molten glass. It would fill up this mold. They'd take the mold out and allow it to cool. Now, if you want to make a container something that could hold stuff like a vase or a perfume bottle, the glassmakers

used a process called core forming. And yeah, I realized, I'm already getting a little far away from talking about telescopes and lenses. But I also think this process is super neat, so I want to explain it briefly. First, the glassmaker would determine what the interior shape of this object was going to be, so, for talking about a bottle, whether it's going to be tall and narrow, or whether it was going to be a wide jug, something along

those lines. Then they would create the core out of a mixture of clay, sand, water, and uh poop or dung if you prefer, and then they would shape that into the rough form they wanted. Before they would insert a metal rod into one end of it, the essentially the end that would be in the open part of the container. They would then allow this core to dry. After it dried, the glassmaker would use tools to further refine the shape of the core, trimming it, filing it down,

that kind of thing. Once finalized, Once it's in that final shape, the glassmaker would heat up a mixture of sand, lime, and soda in a crucible in a furnace, creating a molten glass inside that crucible. Then they would insert this core into that molten glass, hold down the metal rod. They would slowly twirl the core within the molten glass, getting a full coating on the core, sort of like

coating a candy apple. The glassmaker would then remove this let cool a little bit, and use some other tools like pincers for example, to shape the glass while it was still a pliable and then after it had cooled down a bit, they might reheat it a little to to soften the glass, maybe add different colors of glass as decorations on top of it. You could twirl a line of molten glass on top of another layer, have contrasting colors and decorated that way. You might want to

add things like handles to say a pot. Glassmakers would then change the color of the glass, by the way, by by mixing in metal oxides, because different metals would produce different colors. The whole process is super neat to watch. There's actually a lot of videos on YouTube about this process, so if it sounds interesting to you should really check it out because it's pretty neat to see how these

ancient glassmakers would make this stuff. Anyway, glass was incredibly useful and it was much sought after, and these early examples I'm talking about we're really interesting. But the glass they produced were not at all suitable for creating any sort of lens. Those would have to wait for a couple of thousand years. But the foundation for it came

from a pretty simple observation. Water has a magnifying effect, and humans in the ancient world noticed this and wondered, is there a way we could replicate this, where we could create a way to magnify stuff without having to use water. This led to ancient Egyptians and Mesopotamians experimenting with polished crystals, usually using courts around seven fifty b C. One such lens, the Nimrod lens, was made sometime around

then in ancient Assyria. Smartie pants Greek and Roman philosophers began to hypothesize about what was actually going on with these materials, What was creating this magnification effect, how did it really how did it really work? They made some progress over the centuries and sussing things out, but the fall of the Roman Empire would set the world back more than a step or two. A lot of learning

was lost, a lot of progress was halted. One place that continued the academic exploration of what was going on in the world of optics was in the Middle East, and this is probably where the Robin Hood crew got their idea for including a telescope in their screenplay. A few influential mathematicians and writers in the Middle East published their thoughts on what was going on, and they got the basics pretty much right. So what is going on? Well, we have to remember that vision is all about light,

our perception of light. We see stuff because light from some source has reflected off of stuff. The light passes through the lens of our eyes, and the lens directs light to the retina. You can think of the lens as a method of bending light toward a point. In this case, the lens of our eyes bends light so that it hits our retina, which in turn then sends signals to our brains, and that interprets the information it

receives in such a way that we experience vision. So what we see is a filtered representation of what is actually out there according to the light that we're able to perceive. There's stuff well outside the visible spectrum. You know, there's infrared light, there's ultraviolet light, and then beyond that's out there too, but we can't see it without the

aid of technology. And even when we do use technology, what we're really looking at is a conversion of those types of light into something we can actually perceive within the visible spectrum. A lens is a transparent material with at least one curved surface, and the curved surface redirects light. This is called refraction. The lens bends the light rays

and changes the direction of travel. So in a vacuum, light will travel in a straight line, but the path of light changes as it moves through different materials, particularly as it transitions from one material to another. So when we talk about the speed of light, we typically are talking about light as it travels through a vacuum, because then the speed of light is consistent, it does not change it, and it's also the fastest stuff that we

know about in the universe. So when light moves through a different material, transparent material, it slows down a bit compared to how fast it travels through a vacuum. So we can divide n is into two very broad categories, convex lenses and concave lenses. A convex or positive lens bulges outward. This causes incoming rays of light to converge on one another, concentrating on a focal point behind the lens.

So you could use stuff like this to concentrate light into a point and then use that to start a fire, for example with a magnifying glass. Telescopes also use these sort of lenses as their object lens. Will talk about that in a second, so or objective lens. I should say, So, if you think of this in a in a sense of an illustration, and you have a convex lens, remember

it bulges out on either side. In this simple example, you would have parallel rays of light coming in from the outside hitting that convex lens, and then they would all start to tilt inwards of each other, converging to a point further out from that lens. And the point where they actually do converge is the focal point for that lens. We'll get back to that. Then you've got concave or diverging lenses. The surface of a concave lens

bends inward. It's like a bowl, it bends inside. So when parallel rays of light hit a concave lens, of lights coming from outside traveling in those straight lines hits the concave lens, they then bend away from each other. They move further out from each other. So a projector might use a concave lens to spread rays out across a larger surface, like a movie screen. Now that's not to say all lenses are either convex or concave. You can make lenses with elements of each or other parts

that These are called compound lenses. So it can get pretty complicated. But we're gonna really focus on there. It is again focus We're gonna focus on the simpler versions. Now. Early lenses like the Nimrod lens were made from quartz crystal and ground down and polished to create a magnification effect. This effect was not particularly strong, but it did show that it was possible to manufacture refracting lenses. This led

to more research and hypothesizing. In the eleventh century, Arabic scholars were writing about the early signs of optics, carrying on the tradition begun by the Greek and Roman philosophers. By the thirteenth century Italian inventors had figured out how to grind lenses suitable for use as spectacles. Now, these were essentially a pair of magnifying glasses that one would

wear a hold up to your eyes. And there were a lot of different stories about who invented eyeglasses, though many of these lack any substantiating evidence, and a few have been uncovered as being outright hoaxes. Why is that, well, because often it's a matter of local pride to lay claim to an inventor of a transformative technology, and then you can so that, oh, your village or town, or city or country was their home, and therefore you are

all elevated in relation to that. Something that surprised me when I looked into all this was that inventors created the microscope before they created the telescope. I had always assumed the opposite was true. Hans Libacy, whom I mentioned earlier as the person most people credit as the quote unquote inventor of the telescope, may also have invented the microscope, but others say that honor should go to Hans and

Zacharias Jansen. They were a father son team of spectacle makers who happened to live in the very same town as Liberacy. So whomever invented the darned thing appears to have been living in Holland, specifically in Middleburg. I guess stuff was always sort of fuzzy there and they just really needed a closer look whomever was responsible. The earliest records we have for a microscope date back to the fteen nineties. The microscope used a pair or sometimes more,

of magnifying lenses, and they weren't super powerful microscopes. They were only capable of around three to nine times magnification. Skipping ahead a few decades to Liberty in his patent application, at least one version of his story involves him discovering the potential for a telescope essentially by chance. Supposedly, according to the story, Lipper she got an order from a customer to make two lenses. One lens was going to be convex, thus a convergent and magnifying lens. The other

was to be slightly concave or divergent. So he makes the two lenses as requested, and the customer comes in, picks up the two lenses, holds one of them close to his eye, one further away from his eye and looks through them, and then happily pays for the order and leaves. Then, according to this story Lippor, she decides, what the heck was that about? I gotta make a pair of lenses to find out why that was what

does that mean? So he goes. He makes essentially a copy of what he had already made for this customer, just to see what the heck this is all about, holds up the concave lens close to his eye the convex lens further away, and then is astonished to find out that through this combination he's able to view an image of a church across town as if it were right in front of him. It has magnified the image significantly, and thus, according to this possibly apocryphal story, the telescope

was born. He sent a notice to the States General of the Netherlands for this patent, and it would have extended a patent for thirty years. He actually offered up a couple of different options. He said, well, if you don't want to do that, you could give me an annual pension from the government, and in return, if you do this, I'll promise I will not sell this telescope invention to foreign powers, and thus the Netherlands will have

a superiority in that regard. Uh Zachary Jensen, the aforementioned son in that father son duo that worked on the microscope, would claim that he invented the telescope. And there was a third inventor, Jacob Matthias, who disputed Liberty's claim as inventor as well. So ultimately the government of the Netherlands said, we can't give anyone a patent on this. It's widely known already people are already making these, so there's no

way of knowing who owns the rights to this. However, they did give Liberty and a reward of nine hundred florins, which I am told is indeed a princely some in those days. When I come back, I'll explain more about the physics of light within a simple telescope before we continue our journey towards how modern telescopes work today. But first let's take a quick break. Now, one thing I didn't really cover in that first section of the podcast

is why the heck do we need telescopes? I mean, what is it about our vision that has this limiting factor in the first place. Why are smaller objects or objects that are much further away or both, why are they hard to see? Well, remember when I said that when we see something, what's actually happening is that the lens of our eye is directing light reflected off that

object and sending it to our retina. Well, you can think of the retina as being kind of like a sensor, and it's picking up that light, and smaller objects or stuff that's further away take up less space on that sensor, So that's part of it. It's just it's it's taking up a tinier amount of space on the retina, so

we're getting less information to our brains. Also, our eyes are gathering lots of light reflected off of lots of surfaces, and the light coming from a small, distant object can be dwarfed by the light coming from everything else, and eventually the object is too small or too far away for any light reflected off of it to be read, just stirred by our retinas. It's not that the light isn't getting to us, but it's so small compared to

everything else that we can't register it. We can't recognize it, so to see it more clearly, we would need a lens that could take the light reflected off that object and then spread that light across more of the surface of the retina, and telescopes do that. And there are a couple of different ways we can achieve this with

optical telescopes. One is through the lenses I've mentioned already, that would be called a refracting telescope, and the other is through mirrors, which will get too later, and those are reflecting telescopes. So let's start off with refracting telescopes. A simple refracting telescope uses a pair of lenses, like what Lipacy discovered back in six eight. The objective lens collects light from distant objects to a point of focus

that's within the telescope itself. So again, now imagine you've got a lens at the end of a tube and the peril rays are coming in and they hit this this convex lens, the objective lens, and because it's a convex lens, it bends the lights. So now the rays are now converging into the tube to a focal point, so they're bending inwards with relation to the tube within the body of the telescope. Itself. Uh. Now with a modern day telescope that's not a Galileean telescope, which I'll

get to in a second. Uh, those rays would hit a focal point and they don't just stop. They're right. It's not like the rays of light all converge into a point of space and then just create a point of light. Those rays will continue on in a straight line. So now they're diverging from one another. They keep on going until they hit something and they reflect off of it.

So the objective lens faces out into the world, and the other lens is the eyepiece or ocular lens, and that magnifies that light from within the telescope and spread it out so that that light takes up more of the space on your retina. So these diverging rays hit that second lens. That second lens then bends the light in a way that directs it towards the eye of the person using the telescope in a in a parallel fashion,

So it returns the light to a parallel alignment. So what you view through that eye piece is a virtual representation of the real thing that the objective lens has in focus. And this virtual object is much closer to your eye than the real object is, so you get the effective magnification lipatis. Early telescopes can magnify stuff to about three times their relative size to the viewer's perspective,

so not incredible, but an improvement. One interesting point about this type of telescope if we were talking specifically about using convex lenses on both the objective lens and the ocular lens, the eye piece lens or the optical lens, if you prefer if you're using both of those as convex lenses, and you're you've got the focal point inside the telescope itself, the second lenses behind that focal point. As the light converges and then diverges within the telescope,

the image flips upside down. So if you draw this out, it all makes sense. The light rays are coming from the outside world, right, and the light rays that are on the top if you think of it in respect of the telescope, the top of the telescope part, and you're looking at a cross section of it, they get bent so that they aimed downward relative to the telescope. The light rays coming from the bottom side of the lens, for example, then get bent upward with respect to the telescope,

and then they continue on their journey. They hit that focal point and they keep going in a straight line. Uh. And so the light that was at the bottom of the objective lenses at the top of the optical lens or the the ocular lens. The light that was the top of the objective lens is at the bottom of the I piece lens. So that's why if you were looking through such a telescope, the object you were looking

at would be upside down. Uh. If we use such a telescope to look at a celestial body, that's not a big deal because top and bottom in space is largely unimportant. If we wanted to use it in a terrestrial sense, like you wanted to use the telescope to look at stuff around you on Earth, Like let's say that you have a spyglass and you're a pirate, then looking at a distant object might be a bit of a surprise because it would suddenly be flipped upside down.

Modern telescopes use stuff like prisms and mirrors to correct for that vertical inversion. They're called erectors. But what about old telescopes before we figured that out? We're all those pirates we see in romanticized movies looking at stuff upside down the whole time. Well no, so, while my description of objective lenses and eyepieces and all that sort of

stuff is accurate. From modern refracting telescopes, the type used by astronomers and seafarers from around oh say, sixteen ten to about sixteen seventy or so followed the Galilean method. Galileo began using telescopes for astronomical observations not long after Liberacy's work became widely known. So like by six ten, Galileo, like Libacy, used a convex lens as the objective lens, and a concave or diverging or negative lens as the

eye piece lens. So like coming in through the objective lens would bend inward towards a focal point, the diverging lens would reverse the direction of the bend before the rays could hit the user's eye, so the top and bottom wouldn't switch, everything would still be in the proper alignment. As the Institute and Museum of the History of Science puts it, quote, the eye piece is situated in front of the focal point of the objective at a distance from the focal point equal to the focal length of

the eye piece end quote. That gets a little confusing, but if you were to draw it out, it makes a lot of sense. You would have the convex objective lens at the front of the telescope. Lights coming from outside world in parallel rays. It hits that lens and it bends inward, just as we've been talking about all the way up through this podcast, they start to converge

on a focal point that's behind the lens. However, before it gets to the point where all those rays have converged into a single point of space, those rays hit the eye piece lens, the concave lens, So instead of all converging on a focal point, they first hit this concave lens, which then bends the light again, and then the concave lens causes the rays to diverge, returning to

a parallel arrangement. The The early inventors learned that there was a precise art to getting the distance correct between these two lenses. You couldn't just have them one in front of the other and everything works out perfectly. To really get it right, you needed to take the absolute value of the focal length of each lens and then calculate the difference between them. The difference represented the distance between the two lenses you would need to produce the

magnification effect you wanted. So for a Galileean telescope, the distance between the objective lens and the I piece or optical lens is equal to the algebraic sum of the two lenses focal lengths. That is, the distance between the lens and its focal point. So concave lenses actually have a negative focal point. The focal point of a concave lens is in front of the lens, not behind the lens. It's a little counterintuitive. So you add a positive value,

which is the convex lenses focal point. The focal point for a convex lens is behind it. Then you add the negative value that's the concave lenses focal point, and then you get the difference essentially, because it would have been the same as if you subtracted a positive sum from another positive sum. The result is how far apart those two lenses should be to produce the magnification effect. Now, the amount of that magnification is also dependent upon the

focal length of the two lenses. Specifically, it depends upon the ratio between the focal length of the objective lens and then of the I piece lens. So you take the objective lens focal length, you divide it by the focal length of the optical lens. And later telescopes ones that would use two convex lenses, rather than adding those two focal lenks together, you would subtract the focal length of the optical lens from the focal length of the

objective lens. Now, remember that in that case, the focal length rh lens is a positive value. That's the only reason that we had to add the two figures with the Galilean telescope, because one of the values was negative. The greater the diameter of the objective lens, the one that's facing out to the world, the more light it can collect. That seems pretty obvious, right. The bigger the lens, the more light it's going to be able to redirect

inward to the telescope. By the way, the reason why telescopes even have a tube there are a couple of reasons. One is to keep out dust and other things that could obscure the lenses, but another is it helps block out any light that you don't want to come and hit your eye. You want to really focus on whatever object you're looking at. So the greater the diameter or aperture of the objective, the more light it can collect. Generally speaking, the more light it collects, the brighter the

distant image will actually be. And the greater the magnification of your telescope, which again depends upon the relationship between the focal length of lenses, the less field of view you would end up having. So the objective lens die ameter was what determines how much light comes in. It does not necessarily determine how much magnification you get. That is based more on the relationship between that lens and

the I piece lens. But then the amount of magnification you get determines how much field of view you have. If it's a greater amount of magnification, you're going to see less of the night sky in the view of your telescope. Now, there are practical limits that you hit using lenses, because the bigger the lens, the more light it can collect. But it also means that those lens lenses have have more mass. That means the telescopes themselves

get heavier as a result. Moreover, if a lens is too heavy, the weight can actually affect the shape of the lens. It can warp it. And since the lens shape determines where the light is going to go, that's a bad thing. If you've designed a lens to direct light in a very specific way, and then the lens warps under its own weight, the light's not gonna go where you plan, and so you start to reach practical

limits of what you can do using refracting telescopes. The largest refracting telescope objective lens that's still in use today is installed at the Yorkey's Observatory in Wisconsin. The lens on that telescope measures one meter across or or a little more than three feet. In other words, it weighs around twenty six tons. That's how heavy glass gets when you're looking at this, because remember it's a convex lens, it bulges out. So it's not just that it's a

flat sheet of glass. It's not flat, it's it's curved. So this is obviously a little heavier than what you would use in the backyard telescope also I said still in use, but technically the Yerkeys Observatory has been closed to the public since the spring of two thousand eighteen, when the University of Chicago announced it was seeking a party to purchase this observatory and telescope and essentially take it off university hands, which has not yet happened as

the recording of this episode. An other practical limitation of refracting telescopes is that the lens must be in really good shape right, so scratches, smudges, dust, all that can make it difficult for light to pass through the lens. And there's also the issue with lost light. Some of the light hitting the lens doesn't pass through the lens, it will reflect off the lens, and we see this

in our daily lives. If you look at a window and you see your reflection and the window is transparent, then that reflection is proof that some of the light hitting that window is not passing through the glass. Instead it's bouncing off the glass. The same thing is true for telescope lenses, and the thicker and larger the lens, the more light is going to be lost due to reflection. Another limitation is called chromatic aberration, which sounds like a

monster from Dungeons and Dragons. But this all has to do with the fact that light is made up of many wavelengths, which we perceive as different colors. Those different wavelengths have different focal lengths. The focal length of blue light is different than the focal length for red light, and these two wavelengths are pretty far apart on the spectrum,

which I'm sure you remember if you remember Roy g BV. Now, what this means to us using telescopes is that the different colors of light will not quite line up when creating the image of the thing we're trying to look at. The effect isn't enormous, but it's enough to create a fringe of color around images, sort of like a rainbow halo effect almost. And adding in other lenses and various combinations can correct for chromatic aberration. But adding more lenses

means telescopes get way more expensive, delicate, and heavy. There's a different approach that doesn't rely on lenses at all, and those are reflecting telescopes, and I'll explain more about those in just a second. Before we figured out how to you lots of combinations of lenses and prisms to correct for a chromatic aberration and other limitations of refracting telescopes. There was another smarty pants who came up with a different solution. That smarty pants would be Sir Isaac Newton,

who when not dodging falling apples or inventing calculus. And yeah, I know he wasn't the only one to invent calculus. He was coming up with nifty ways to improve telescopes, and he did this around the sixteen seventies. Newton's solution, which had previously been suggested by folks like Galileo, was to rely upon a curved mirror rather than a lens to gather light. The mirror would sit at the base of the telescope. So again, if you think of the telescope as a tube, then the mirror would be at

the bottom of the tube. The top of the tube would be open, open to the night sky. The curved mirror, a parabolic mirror, would reflect light so that all the parallel rays come into the telescope would hit the mirror and then reflect off on a converging pathway. So similar in execution. If you can think of it that way, and maybe not execution. Similar in effect to how a convex lens bends light to converge on a focal point, the parabolic mirror would reflect light to converge on a

focal point inside the telescope. However, Newton mounted a second mirror sitting just ahead of where the focal point would be, so in between the parabolic mirror and that mirror's focal point. This the secondary mirror would reflect light coming from the objective mirror at around a ninety degree angle toward an eyepiece, which would provide magnification of the virtual image produced there. So the light coming in from the main mirror bounces

off a second mirror and then you can see that light. Otherwise, the parabolic mirror would just reflect light back out of the open into the telescope. That would do you no good. The only way to look into it would be to put your head in the telescope, and then you're blocking the light that's coming into it. So the secondary mirror was to redirect light so you could actually see what

this telescope was observing. So, instead of an objective lens to capture and bend light, Newton's telescope had an objective mirror like a refracting telescope, the amount of light captured is dependent upon the size of the objective component, but a mirror's thickness doesn't have to change as you increase its diameter. It doesn't bulge out, so you can make a really thin, really large parabolic mirror. By contrast, the refracting lens would get thicker as you increase the diameter

in order to get the proper refracting properties. So the switch to a reflecting mirror meant you could construct much larger telescopes without having to worry about dealing with really heavy, very delicate lenses. Even a really big reflecting telescope could be mounted on a sturdy support structure and the mirror would retain its parabolic shape compared to those glass lenses that would eventually warp from the weight of the lens itself.

And because the light was bouncing off mirrors rather than passing through lenses, Newton didn't have to worry about chromatic aberration. However, reflecting telescopes had their own sets of limitations. Early on, a big limitation was focal length. The reflecting telescopes were limited having a relatively short focal length, and since focal length is tied to magnification, that meant reflecting telescopes were largely limited and how much magnification you could get out

of them. This would later be addressed with innovations and telescope design, but it was a bit of a limitation in Newton's time. Also, while the telescope has had a relatively short focal point, they also had a relatively large field of view, so you can see more of the night sky in the view using a reflecting telescope than a comparatively similar refracting telescope. Another small limitation was the reflecting mirror mounted above the objective mirror, you know, the

one that's in between the objective mirror and its focal point. Well, it would block a little bit of the light coming into the telescope. It wouldn't block any of your view because essentially every point of the mirror would have a full version of the image that was coming into the telescope, So you were getting a full view, but you were blocking some of the light coming into the telescope, so the image would be a little more dim than otherwise

would be. So the bigger this reflecting mirror was the more light it would block, and the dem or the resulting image would be. The curved mirror also meant that objects along the perimeter of the field of view would be slightly warped. So anything in the center of your view would be pretty accurate, but the closer you got to the edge of your you, the more warped it would get, and you would get these elongated images. So if you're looking at a star, it might look more

like a tear drop or a comment. So that was a little bit of a of a setback, or at least a drawback, I should say. So, yeah, these telescopes can get pretty big. The biggest in operation right now is the Grund telescope Eo Canarius in La Palma, Spain, as a diameter of ten point four meters or thirty four point two feet. Now, remember, the largest refracting telescope has an objective lens diameter of one meter, So this reflecting telescope has an objective mirror ten times that diameter.

That's huge. Now, the mirror is also not a single unbroken surface. It's not one ten point four meter across mirror. It's actually made up of thirty six hexagonal mirrors that fit together snugly, kind of like a puzzle piece. But there's an even larger reflecting telescope that's currently in development. It's called the European Extremely Large Telescope. Seems pretty self explanatory.

It's gonna have a reflecting objective mirror that measures approximately forty meters in diameter, according to the European Southern Observatory. The telescope will correct for atmospheric distortions, which is one of the problems that we have just using telescopes here on Earth. It's the fact that we have this pesky atmosphere that gets in the way sometimes. Uh. The atmosphere is why stars appear to twinkle when we look at them, so that can be a problem when you're trying to

magnify all of that stuff. But this one's supposed to correct for that. It's also supposed to be able to collect thirteen times more light than any other optical telescope we have here on Earth, and again, according to the e s O, provide images that are sixteen times more sharp than the Hubble Space telescope was able to. The plan is to have this telescope ready to make observations starting in twenty twenty five. Speaking of the Hubble, it

is itself a reflecting telescope. Specifically, it's a type of reflecting telescope called a Cassegrain reflector, which uses a pair of curved mirrors. The objective mirror is that concave parabolic mirror design that I talked about just a moment ago, but mounted above that, instead of a mirror that reflects that image ninety degrees, it's actually a mirror facing the first one, and this one is a convex mirror, so

it bulges outward, not curves inward. The parabolic mirror reflects incoming light toward a focal point, and mounted ahead of that focal point is this convex mirror, which then reflects light back down the telescope in a converging point, and the main parabolic mirror at the base of the telescope has a small hole in the center that allows light

to pass through. The idea for the Hubble and other space telescopes was that by putting telescopes in orbit and thus outside of our atmosp fear, we could get an unimpeded look at distant celestial bodies. You wouldn't have to worry about atmospheric distortion or light pollution from terrestrial sources. Unfortunately, after the Hubble Telescope had already launched into orbit, it

became clear that the objective mirror wasn't shaped correctly. It was just slightly too flat by the order of a couple of micrometers, so a very small error, but enough to be catastrophic. That was enough to introduce spherical aberration, which translates to people like you and me, as the telescope was returning fuzzy images and it was supposed to be super sharp, gorgeous images of the the galaxies around us. Now.

Eventually astronomers were able to come up with a solution, though it would mean sending astronauts back up to the Hubble Space Telescope to install a couple of additional mirrors to correct for that issue, and in the process they had to also remove some of the instrumentation that was intended to get there other types of cosmological data. This is what we would call a very expensive boo boo.

The James Webb Space Telescope, which is scheduled to launch in twenty one, is of a similar design, but we'll be exploring the universe. By collecting infrared light, which is outside the visible spectrum, it will look at light that is four times fainter than what current telescopes can detect, and that means it can detect light from very distant sources. And in space, you can think of distance and time as being very closely related because it takes time for

light to travel distances. Now, light moves wicked fast. It's the fastest stuff in the universe as far as we can tell, but even so, it still takes time to get from point A to point B. So when we look up at stars, the light we're seeing from stars might have taken a journey that lasted millions of years, so we're effectively looking into the long distant past of those celestial bodies. We're not seeing the star as it

is today. We're seeing the star as it was when that light left the star, possibly millions of years ago. And the James Webb is going to collect light from further away than we've ever managed to do up to now, meaning we'll be looking much further back into the past of the universe than we've ever been capable of doing, which is pretty darn cool. Now there's a lot I didn't cover in this episode. For one thing, I stuck with optical telescopes, but there are other kinds like radio telescopes.

For another, I didn't really talk about stuff like the erectors, which are those devices that are meant to reverse that vertical flipping thing that I talked about with refracting telescopes if they're using two convex lenses. But I figured this was a good overview into the super interesting piece of technology that has at its heart very few components. But those components have to be precisely designed, constructed, and placed

in relation to one another. So it's a real testament to human ingenuity and also how sometimes the most impressive technologies are not necessarily the most complicated when you get down to it. If you guys have suggestions for future episodes of tech Stuff, let me know. Send me an email. The addresses tech Stuff at how stuparks dot com. Drop on by our website that's text Stuff podcast dot com. You're gonna find an archive of all of our past episodes. You can do a search find out if the topic

you have in mind has already been covered. If not, let me know. You can also find links to where we are on social media in places like Twitter and Facebook. Over there, so you can drop me a line there, and don't forget. We also have a link to our online store, where every purchase you make goes to help the show, and we greatly appreciate it, and I'll talk to you again really soon. Text Stuff is a production

of I Heart Radio's How Stuff Works. For more podcasts from i heeart Radio, visit the I heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows. Eight