WEBVTT - TechStuff Looks through a Telescope 0:00:04.240 --> 0:00:07.240 Welcome to tech Stuff, a production of I Heart Radios 0:00:07.320 --> 0:00:14.280 How Stuff Works. Hey there, and welcome to tech Stuff. 0:00:14.480 --> 0:00:18.000 I'm your host, Jonathan Strickland. I'm an executive producer with 0:00:18.040 --> 0:00:19.920 How Stuff Works in My Heart Radio and I love 0:00:20.079 --> 0:00:26.759 all things tech and way back in one a very 0:00:26.840 --> 0:00:31.320 not good film titled Robin Hood Prince of Thieves debut 0:00:31.880 --> 0:00:36.040 and don't at me. That movie is trash. I loved 0:00:36.040 --> 0:00:39.000 it as a kid, but it is garbage. It starred 0:00:39.159 --> 0:00:42.080 Kevin Costner as Robin of Locksley, better known as the 0:00:42.120 --> 0:00:44.960 outlaw Robin Hood, and the film is set in eleven 0:00:45.120 --> 0:00:49.559 ninety four and Robin had a lot of problems. The 0:00:49.600 --> 0:00:52.839 Sheriff Nottingham was on his back, his beloved made Marian 0:00:52.920 --> 0:00:56.280 gets kidnapped, and his accent kept going in and out, 0:00:56.320 --> 0:00:58.320 so you can imagine the stress he was under. But 0:00:58.360 --> 0:01:01.520 he also had some advance diages. Now, one of those 0:01:01.920 --> 0:01:06.240 was his ingenious companion a Zeem played by Morgan Freeman. 0:01:06.480 --> 0:01:09.480 And in one scene, a Zeem helps Robin get a 0:01:09.520 --> 0:01:14.120 better look at some adversaries using a telescope. Now that 0:01:14.240 --> 0:01:17.640 scene is meant to establish that a Zeem's homeland often 0:01:17.720 --> 0:01:21.320 viewed as a backward and savage place through the eyes 0:01:21.360 --> 0:01:25.240 of England, and by extension, the West in general is 0:01:25.280 --> 0:01:29.640 actually home to great learning and innovation. And that part 0:01:30.000 --> 0:01:32.199 was true. I mean, the Middle East has a long 0:01:32.360 --> 0:01:36.800 history of phenomenal achievements, but inventing a telescope in the 0:01:36.880 --> 0:01:42.120 late twelfth century is not among them. That was historically inaccurate, 0:01:42.560 --> 0:01:45.200 probably the least of the historical inaccuracies in that film. 0:01:45.200 --> 0:01:47.920 But still I wanted to start with this because this 0:01:48.000 --> 0:01:50.680 was just one of the many fictions and fallacies in 0:01:50.680 --> 0:01:52.160 The Robin Hood. But I figured it was a fun 0:01:52.200 --> 0:01:55.160 place to start off this episode about the telescope. We're 0:01:55.160 --> 0:01:58.120 gonna look at where it actually did come from and 0:01:58.240 --> 0:02:02.400 how basic telescopes were. I guess you could say it's 0:02:02.480 --> 0:02:07.960 the focus of this episode. H m hm. And So 0:02:08.040 --> 0:02:11.000 while I now will leave the film Robin Hood Prince 0:02:11.000 --> 0:02:13.840 of Thieves behind, just remember that everything I do, I 0:02:13.960 --> 0:02:17.359 do it for you. Now, As is the case with 0:02:17.480 --> 0:02:21.200 much of technology, it's not really possible for me to 0:02:21.240 --> 0:02:24.120 tell you who invented the first telescope. I can tell 0:02:24.160 --> 0:02:27.880 you that the person most folks credit with inventing the 0:02:27.880 --> 0:02:34.720 telescope was the German Dutch inventor Hans Lipperty. He applied 0:02:34.800 --> 0:02:38.359 for a patent for an invention he called the geiker 0:02:39.680 --> 0:02:43.560 or kaiker. It's kind of hard for me to pronounce 0:02:43.600 --> 0:02:48.359 because I don't speak Dutch, but it means looker in Dutch. 0:02:48.840 --> 0:02:51.600 We'll come back to it. For this invention to be 0:02:51.639 --> 0:02:54.800 possible at all, the first thing that has to happen 0:02:54.840 --> 0:02:57.639 is that humans needed to learn how to make glass. 0:02:58.280 --> 0:03:01.320 Now we don't have a record of that actually happened, 0:03:01.360 --> 0:03:04.680 but our best guess is that glassmaking became an actual 0:03:04.800 --> 0:03:09.680 thing around four thousand years ago in Mesa Potamia, as 0:03:09.760 --> 0:03:13.559 the B. Fifty two s would say, a region called Ptolemace, 0:03:13.800 --> 0:03:17.920 which is in now modern day Israel, was particularly known 0:03:18.000 --> 0:03:22.040 for this, having sand that was suitable for glassmaking, and 0:03:22.240 --> 0:03:27.399 early glassmakers would mix sand, soda, and lime which could 0:03:27.400 --> 0:03:30.160 then be heated in a furnace to create molten glass. 0:03:30.600 --> 0:03:35.520 To make a solid glass object, this mixture of sand, soda, 0:03:35.560 --> 0:03:38.440 and lime would first be put into an open mold, 0:03:39.240 --> 0:03:42.080 and the mold would be placed in the furnace, which 0:03:42.120 --> 0:03:45.360 would be heated up enough for the mixture to become 0:03:45.360 --> 0:03:48.240 molten glass. It would fill up this mold. They'd take 0:03:48.320 --> 0:03:51.160 the mold out and allow it to cool. Now, if 0:03:51.200 --> 0:03:53.480 you want to make a container something that could hold 0:03:53.560 --> 0:03:57.240 stuff like a vase or a perfume bottle, the glassmakers 0:03:57.320 --> 0:04:01.080 used a process called core forming. And yeah, I realized, 0:04:01.080 --> 0:04:03.640 I'm already getting a little far away from talking about 0:04:03.640 --> 0:04:07.560 telescopes and lenses. But I also think this process is 0:04:07.560 --> 0:04:10.560 super neat, so I want to explain it briefly. First, 0:04:10.960 --> 0:04:14.600 the glassmaker would determine what the interior shape of this 0:04:14.680 --> 0:04:17.200 object was going to be, so, for talking about a bottle, 0:04:17.680 --> 0:04:19.719 whether it's going to be tall and narrow, or whether 0:04:19.760 --> 0:04:21.760 it was going to be a wide jug, something along 0:04:21.760 --> 0:04:25.279 those lines. Then they would create the core out of 0:04:25.320 --> 0:04:31.680 a mixture of clay, sand, water, and uh poop or 0:04:31.960 --> 0:04:34.960 dung if you prefer, and then they would shape that 0:04:35.080 --> 0:04:38.640 into the rough form they wanted. Before they would insert 0:04:38.680 --> 0:04:41.520 a metal rod into one end of it, the essentially 0:04:41.600 --> 0:04:43.640 the end that would be in the open part of 0:04:43.640 --> 0:04:47.479 the container. They would then allow this core to dry. 0:04:47.720 --> 0:04:51.000 After it dried, the glassmaker would use tools to further 0:04:51.080 --> 0:04:55.279 refine the shape of the core, trimming it, filing it down, 0:04:55.360 --> 0:04:58.560 that kind of thing. Once finalized, Once it's in that 0:04:58.680 --> 0:05:02.960 final shape, the glassmaker would heat up a mixture of sand, lime, 0:05:03.000 --> 0:05:06.800 and soda in a crucible in a furnace, creating a 0:05:06.880 --> 0:05:11.120 molten glass inside that crucible. Then they would insert this 0:05:11.360 --> 0:05:16.279 core into that molten glass, hold down the metal rod. 0:05:16.720 --> 0:05:20.080 They would slowly twirl the core within the molten glass, 0:05:20.279 --> 0:05:22.360 getting a full coating on the core, sort of like 0:05:22.520 --> 0:05:27.120 coating a candy apple. The glassmaker would then remove this 0:05:27.320 --> 0:05:29.920 let cool a little bit, and use some other tools 0:05:30.000 --> 0:05:33.240 like pincers for example, to shape the glass while it 0:05:33.279 --> 0:05:35.919 was still a pliable and then after it had cooled 0:05:35.920 --> 0:05:37.960 down a bit, they might reheat it a little to 0:05:37.960 --> 0:05:41.599 to soften the glass, maybe add different colors of glass 0:05:41.720 --> 0:05:45.320 as decorations on top of it. You could twirl a 0:05:45.480 --> 0:05:48.919 line of molten glass on top of another layer, have 0:05:49.040 --> 0:05:52.080 contrasting colors and decorated that way. You might want to 0:05:52.120 --> 0:05:56.440 add things like handles to say a pot. Glassmakers would 0:05:56.440 --> 0:05:59.200 then change the color of the glass, by the way, 0:05:59.240 --> 0:06:02.479 by by mixing in metal oxides, because different metals would 0:06:02.560 --> 0:06:06.000 produce different colors. The whole process is super neat to watch. 0:06:06.080 --> 0:06:09.680 There's actually a lot of videos on YouTube about this process, 0:06:09.720 --> 0:06:12.080 so if it sounds interesting to you should really check 0:06:12.120 --> 0:06:14.320 it out because it's pretty neat to see how these 0:06:14.360 --> 0:06:18.520 ancient glassmakers would make this stuff. Anyway, glass was incredibly 0:06:18.600 --> 0:06:21.920 useful and it was much sought after, and these early 0:06:21.960 --> 0:06:26.720 examples I'm talking about we're really interesting. But the glass 0:06:26.760 --> 0:06:30.080 they produced were not at all suitable for creating any 0:06:30.120 --> 0:06:34.240 sort of lens. Those would have to wait for a 0:06:34.279 --> 0:06:37.839 couple of thousand years. But the foundation for it came 0:06:37.960 --> 0:06:42.960 from a pretty simple observation. Water has a magnifying effect, 0:06:43.400 --> 0:06:46.120 and humans in the ancient world noticed this and wondered, 0:06:46.760 --> 0:06:48.640 is there a way we could replicate this, where we 0:06:48.680 --> 0:06:52.960 could create a way to magnify stuff without having to 0:06:53.120 --> 0:06:58.120 use water. This led to ancient Egyptians and Mesopotamians experimenting 0:06:58.160 --> 0:07:03.160 with polished crystals, usually using courts around seven fifty b C. 0:07:04.320 --> 0:07:08.799 One such lens, the Nimrod lens, was made sometime around 0:07:08.839 --> 0:07:13.520 then in ancient Assyria. Smartie pants Greek and Roman philosophers 0:07:13.520 --> 0:07:16.320 began to hypothesize about what was actually going on with 0:07:16.360 --> 0:07:20.120 these materials, What was creating this magnification effect, how did 0:07:20.200 --> 0:07:23.400 it really how did it really work? They made some 0:07:23.480 --> 0:07:27.080 progress over the centuries and sussing things out, but the 0:07:27.120 --> 0:07:29.600 fall of the Roman Empire would set the world back 0:07:29.800 --> 0:07:32.120 more than a step or two. A lot of learning 0:07:32.160 --> 0:07:35.920 was lost, a lot of progress was halted. One place 0:07:35.960 --> 0:07:39.760 that continued the academic exploration of what was going on 0:07:39.920 --> 0:07:42.320 in the world of optics was in the Middle East, 0:07:42.360 --> 0:07:45.920 and this is probably where the Robin Hood crew got 0:07:45.960 --> 0:07:49.600 their idea for including a telescope in their screenplay. A 0:07:49.640 --> 0:07:53.520 few influential mathematicians and writers in the Middle East published 0:07:53.560 --> 0:07:56.320 their thoughts on what was going on, and they got 0:07:56.400 --> 0:08:00.880 the basics pretty much right. So what is going on? Well, 0:08:01.600 --> 0:08:05.120 we have to remember that vision is all about light, 0:08:05.480 --> 0:08:09.720 our perception of light. We see stuff because light from 0:08:09.840 --> 0:08:14.520 some source has reflected off of stuff. The light passes 0:08:14.520 --> 0:08:17.800 through the lens of our eyes, and the lens directs 0:08:17.920 --> 0:08:20.760 light to the retina. You can think of the lens 0:08:20.800 --> 0:08:23.920 as a method of bending light toward a point. In 0:08:23.920 --> 0:08:26.640 this case, the lens of our eyes bends light so 0:08:26.720 --> 0:08:30.680 that it hits our retina, which in turn then sends 0:08:30.840 --> 0:08:34.480 signals to our brains, and that interprets the information it 0:08:34.559 --> 0:08:37.480 receives in such a way that we experience vision. So 0:08:38.120 --> 0:08:41.680 what we see is a filtered representation of what is 0:08:42.000 --> 0:08:45.280 actually out there according to the light that we're able 0:08:45.320 --> 0:08:49.440 to perceive. There's stuff well outside the visible spectrum. You know, 0:08:49.440 --> 0:08:53.640 there's infrared light, there's ultraviolet light, and then beyond that's 0:08:53.640 --> 0:08:55.800 out there too, but we can't see it without the 0:08:55.840 --> 0:08:58.800 aid of technology. And even when we do use technology, 0:08:59.040 --> 0:09:02.000 what we're really looking at is a conversion of those 0:09:02.040 --> 0:09:04.760 types of light into something we can actually perceive within 0:09:04.800 --> 0:09:09.680 the visible spectrum. A lens is a transparent material with 0:09:09.760 --> 0:09:14.440 at least one curved surface, and the curved surface redirects light. 0:09:15.000 --> 0:09:19.040 This is called refraction. The lens bends the light rays 0:09:19.080 --> 0:09:22.640 and changes the direction of travel. So in a vacuum, 0:09:22.840 --> 0:09:25.720 light will travel in a straight line, but the path 0:09:25.760 --> 0:09:29.640 of light changes as it moves through different materials, particularly 0:09:29.679 --> 0:09:33.360 as it transitions from one material to another. So when 0:09:33.360 --> 0:09:35.880 we talk about the speed of light, we typically are 0:09:35.880 --> 0:09:39.160 talking about light as it travels through a vacuum, because 0:09:39.440 --> 0:09:43.000 then the speed of light is consistent, it does not 0:09:43.280 --> 0:09:46.679 change it, and it's also the fastest stuff that we 0:09:46.720 --> 0:09:51.040 know about in the universe. So when light moves through 0:09:51.360 --> 0:09:55.480 a different material, transparent material, it slows down a bit 0:09:55.559 --> 0:09:59.080 compared to how fast it travels through a vacuum. So 0:09:59.120 --> 0:10:03.079 we can divide n is into two very broad categories, 0:10:03.559 --> 0:10:09.760 convex lenses and concave lenses. A convex or positive lens 0:10:09.800 --> 0:10:14.920 bulges outward. This causes incoming rays of light to converge 0:10:15.000 --> 0:10:19.040 on one another, concentrating on a focal point behind the lens. 0:10:19.120 --> 0:10:22.280 So you could use stuff like this to concentrate light 0:10:22.320 --> 0:10:25.120 into a point and then use that to start a fire, 0:10:25.280 --> 0:10:29.960 for example with a magnifying glass. Telescopes also use these 0:10:30.000 --> 0:10:33.640 sort of lenses as their object lens. Will talk about 0:10:33.679 --> 0:10:37.240 that in a second, so or objective lens. I should say, So, 0:10:38.720 --> 0:10:40.480 if you think of this in a in a sense 0:10:40.520 --> 0:10:44.680 of an illustration, and you have a convex lens, remember 0:10:44.679 --> 0:10:48.040 it bulges out on either side. In this simple example, 0:10:48.440 --> 0:10:51.079 you would have parallel rays of light coming in from 0:10:51.160 --> 0:10:55.480 the outside hitting that convex lens, and then they would 0:10:55.520 --> 0:10:59.360 all start to tilt inwards of each other, converging to 0:10:59.480 --> 0:11:04.000 a point further out from that lens. And the point 0:11:04.000 --> 0:11:07.080 where they actually do converge is the focal point for 0:11:07.240 --> 0:11:09.800 that lens. We'll get back to that. Then you've got 0:11:10.320 --> 0:11:15.640 concave or diverging lenses. The surface of a concave lens 0:11:15.800 --> 0:11:20.200 bends inward. It's like a bowl, it bends inside. So 0:11:20.280 --> 0:11:23.880 when parallel rays of light hit a concave lens, of 0:11:24.200 --> 0:11:27.720 lights coming from outside traveling in those straight lines hits 0:11:27.720 --> 0:11:31.120 the concave lens, they then bend away from each other. 0:11:31.160 --> 0:11:34.280 They move further out from each other. So a projector 0:11:34.360 --> 0:11:37.480 might use a concave lens to spread rays out across 0:11:37.520 --> 0:11:41.480 a larger surface, like a movie screen. Now that's not 0:11:41.559 --> 0:11:45.320 to say all lenses are either convex or concave. You 0:11:45.320 --> 0:11:49.319 can make lenses with elements of each or other parts 0:11:49.320 --> 0:11:52.600 that These are called compound lenses. So it can get 0:11:52.600 --> 0:11:55.800 pretty complicated. But we're gonna really focus on there. It 0:11:55.920 --> 0:12:00.640 is again focus We're gonna focus on the simpler versions. Now. 0:12:00.640 --> 0:12:04.040 Early lenses like the Nimrod lens were made from quartz 0:12:04.040 --> 0:12:07.840 crystal and ground down and polished to create a magnification effect. 0:12:08.400 --> 0:12:11.520 This effect was not particularly strong, but it did show 0:12:11.559 --> 0:12:15.080 that it was possible to manufacture refracting lenses. This led 0:12:15.120 --> 0:12:19.640 to more research and hypothesizing. In the eleventh century, Arabic 0:12:19.720 --> 0:12:22.760 scholars were writing about the early signs of optics, carrying 0:12:22.760 --> 0:12:25.800 on the tradition begun by the Greek and Roman philosophers. 0:12:26.120 --> 0:12:30.080 By the thirteenth century Italian inventors had figured out how 0:12:30.080 --> 0:12:34.920 to grind lenses suitable for use as spectacles. Now, these 0:12:34.960 --> 0:12:38.319 were essentially a pair of magnifying glasses that one would 0:12:38.320 --> 0:12:41.120 wear a hold up to your eyes. And there were 0:12:41.160 --> 0:12:43.960 a lot of different stories about who invented eyeglasses, though 0:12:44.120 --> 0:12:47.000 many of these lack any substantiating evidence, and a few 0:12:47.040 --> 0:12:51.679 have been uncovered as being outright hoaxes. Why is that, well, 0:12:51.760 --> 0:12:54.520 because often it's a matter of local pride to lay 0:12:54.600 --> 0:12:58.920 claim to an inventor of a transformative technology, and then 0:12:59.000 --> 0:13:02.040 you can so that, oh, your village or town, or 0:13:02.080 --> 0:13:05.640 city or country was their home, and therefore you are 0:13:05.679 --> 0:13:10.040 all elevated in relation to that. Something that surprised me 0:13:10.160 --> 0:13:14.040 when I looked into all this was that inventors created 0:13:14.120 --> 0:13:18.800 the microscope before they created the telescope. I had always 0:13:18.800 --> 0:13:23.439 assumed the opposite was true. Hans Libacy, whom I mentioned 0:13:23.440 --> 0:13:26.520 earlier as the person most people credit as the quote 0:13:26.559 --> 0:13:31.520 unquote inventor of the telescope, may also have invented the microscope, 0:13:31.600 --> 0:13:34.440 but others say that honor should go to Hans and 0:13:34.559 --> 0:13:38.680 Zacharias Jansen. They were a father son team of spectacle 0:13:38.720 --> 0:13:41.480 makers who happened to live in the very same town 0:13:41.640 --> 0:13:45.640 as Liberacy. So whomever invented the darned thing appears to 0:13:45.679 --> 0:13:49.280 have been living in Holland, specifically in Middleburg. I guess 0:13:49.480 --> 0:13:52.320 stuff was always sort of fuzzy there and they just 0:13:52.360 --> 0:13:56.680 really needed a closer look whomever was responsible. The earliest 0:13:56.720 --> 0:13:59.840 records we have for a microscope date back to the 0:14:00.000 --> 0:14:03.800 fteen nineties. The microscope used a pair or sometimes more, 0:14:04.360 --> 0:14:08.280 of magnifying lenses, and they weren't super powerful microscopes. They 0:14:08.320 --> 0:14:11.719 were only capable of around three to nine times magnification. 0:14:12.360 --> 0:14:15.520 Skipping ahead a few decades to Liberty in his patent application, 0:14:15.960 --> 0:14:19.000 at least one version of his story involves him discovering 0:14:19.000 --> 0:14:23.720 the potential for a telescope essentially by chance. Supposedly, according 0:14:23.720 --> 0:14:26.440 to the story, Lipper she got an order from a 0:14:26.520 --> 0:14:30.520 customer to make two lenses. One lens was going to 0:14:30.560 --> 0:14:35.120 be convex, thus a convergent and magnifying lens. The other 0:14:35.240 --> 0:14:38.400 was to be slightly concave or divergent. So he makes 0:14:38.440 --> 0:14:41.720 the two lenses as requested, and the customer comes in, 0:14:41.960 --> 0:14:45.080 picks up the two lenses, holds one of them close 0:14:45.240 --> 0:14:48.520 to his eye, one further away from his eye and 0:14:48.640 --> 0:14:51.320 looks through them, and then happily pays for the order 0:14:51.480 --> 0:14:55.720 and leaves. Then, according to this story Lippor, she decides, 0:14:56.240 --> 0:14:58.200 what the heck was that about? I gotta make a 0:14:58.240 --> 0:15:02.880 pair of lenses to find out why that was what 0:15:02.960 --> 0:15:05.840 does that mean? So he goes. He makes essentially a 0:15:05.880 --> 0:15:08.560 copy of what he had already made for this customer, 0:15:08.960 --> 0:15:10.760 just to see what the heck this is all about, 0:15:11.080 --> 0:15:13.680 holds up the concave lens close to his eye the 0:15:13.720 --> 0:15:16.640 convex lens further away, and then is astonished to find 0:15:16.640 --> 0:15:20.240 out that through this combination he's able to view an 0:15:20.280 --> 0:15:23.760 image of a church across town as if it were 0:15:24.120 --> 0:15:27.680 right in front of him. It has magnified the image significantly, 0:15:27.720 --> 0:15:31.640 and thus, according to this possibly apocryphal story, the telescope 0:15:31.680 --> 0:15:35.520 was born. He sent a notice to the States General 0:15:35.800 --> 0:15:39.840 of the Netherlands for this patent, and it would have 0:15:39.960 --> 0:15:43.240 extended a patent for thirty years. He actually offered up 0:15:43.240 --> 0:15:46.360 a couple of different options. He said, well, if you 0:15:46.360 --> 0:15:47.880 don't want to do that, you could give me an 0:15:47.920 --> 0:15:51.200 annual pension from the government, and in return, if you 0:15:51.280 --> 0:15:55.160 do this, I'll promise I will not sell this telescope 0:15:55.160 --> 0:15:58.640 invention to foreign powers, and thus the Netherlands will have 0:15:58.720 --> 0:16:03.800 a superiority in that regard. Uh Zachary Jensen, the aforementioned 0:16:03.960 --> 0:16:07.240 son in that father son duo that worked on the microscope, 0:16:07.640 --> 0:16:10.400 would claim that he invented the telescope. And there was 0:16:10.440 --> 0:16:15.000 a third inventor, Jacob Matthias, who disputed Liberty's claim as 0:16:15.000 --> 0:16:18.280 inventor as well. So ultimately the government of the Netherlands said, 0:16:19.520 --> 0:16:22.840 we can't give anyone a patent on this. It's widely 0:16:22.920 --> 0:16:26.240 known already people are already making these, so there's no 0:16:26.280 --> 0:16:29.040 way of knowing who owns the rights to this. However, 0:16:29.080 --> 0:16:33.200 they did give Liberty and a reward of nine hundred florins, 0:16:33.240 --> 0:16:37.280 which I am told is indeed a princely some in 0:16:37.320 --> 0:16:40.240 those days. When I come back, I'll explain more about 0:16:40.240 --> 0:16:43.760 the physics of light within a simple telescope before we 0:16:43.800 --> 0:16:46.920 continue our journey towards how modern telescopes work today. But 0:16:47.000 --> 0:16:57.200 first let's take a quick break. Now, one thing I 0:16:57.200 --> 0:17:00.680 didn't really cover in that first section of the podcast 0:17:01.120 --> 0:17:03.240 is why the heck do we need telescopes? I mean, 0:17:03.280 --> 0:17:05.720 what is it about our vision that has this limiting 0:17:05.720 --> 0:17:09.520 factor in the first place. Why are smaller objects or 0:17:09.560 --> 0:17:13.040 objects that are much further away or both, why are 0:17:13.080 --> 0:17:16.080 they hard to see? Well, remember when I said that 0:17:16.160 --> 0:17:18.960 when we see something, what's actually happening is that the 0:17:19.080 --> 0:17:22.199 lens of our eye is directing light reflected off that 0:17:22.359 --> 0:17:26.040 object and sending it to our retina. Well, you can 0:17:26.080 --> 0:17:28.680 think of the retina as being kind of like a sensor, 0:17:28.760 --> 0:17:32.480 and it's picking up that light, and smaller objects or 0:17:32.520 --> 0:17:36.840 stuff that's further away take up less space on that sensor, 0:17:37.320 --> 0:17:40.119 So that's part of it. It's just it's it's taking 0:17:40.200 --> 0:17:42.960 up a tinier amount of space on the retina, so 0:17:43.000 --> 0:17:46.000 we're getting less information to our brains. Also, our eyes 0:17:46.040 --> 0:17:49.600 are gathering lots of light reflected off of lots of surfaces, 0:17:49.640 --> 0:17:52.360 and the light coming from a small, distant object can 0:17:52.359 --> 0:17:54.560 be dwarfed by the light coming from everything else, and 0:17:54.600 --> 0:17:57.479 eventually the object is too small or too far away 0:17:57.800 --> 0:17:59.920 for any light reflected off of it to be read, 0:18:00.040 --> 0:18:02.240 just stirred by our retinas. It's not that the light 0:18:02.320 --> 0:18:04.840 isn't getting to us, but it's so small compared to 0:18:04.880 --> 0:18:09.199 everything else that we can't register it. We can't recognize it, 0:18:10.080 --> 0:18:12.600 so to see it more clearly, we would need a 0:18:12.760 --> 0:18:16.200 lens that could take the light reflected off that object 0:18:16.640 --> 0:18:19.560 and then spread that light across more of the surface 0:18:19.680 --> 0:18:22.320 of the retina, and telescopes do that. And there are 0:18:22.240 --> 0:18:24.280 a couple of different ways we can achieve this with 0:18:24.359 --> 0:18:28.200 optical telescopes. One is through the lenses I've mentioned already, 0:18:28.359 --> 0:18:31.479 that would be called a refracting telescope, and the other 0:18:31.640 --> 0:18:33.840 is through mirrors, which will get too later, and those 0:18:33.880 --> 0:18:38.440 are reflecting telescopes. So let's start off with refracting telescopes. 0:18:38.680 --> 0:18:42.919 A simple refracting telescope uses a pair of lenses, like 0:18:42.960 --> 0:18:47.360 what Lipacy discovered back in six eight. The objective lens 0:18:47.760 --> 0:18:52.040 collects light from distant objects to a point of focus 0:18:52.080 --> 0:18:56.640 that's within the telescope itself. So again, now imagine you've 0:18:56.640 --> 0:18:59.400 got a lens at the end of a tube and 0:18:59.480 --> 0:19:02.760 the peril rays are coming in and they hit this 0:19:02.760 --> 0:19:07.240 this convex lens, the objective lens, and because it's a 0:19:07.320 --> 0:19:10.320 convex lens, it bends the lights. So now the rays 0:19:10.359 --> 0:19:14.600 are now converging into the tube to a focal point, 0:19:14.680 --> 0:19:18.560 so they're bending inwards with relation to the tube within 0:19:18.600 --> 0:19:22.640 the body of the telescope. Itself. Uh. Now with a 0:19:22.720 --> 0:19:27.000 modern day telescope that's not a Galileean telescope, which I'll 0:19:27.040 --> 0:19:30.520 get to in a second. Uh, those rays would hit 0:19:30.560 --> 0:19:33.960 a focal point and they don't just stop. They're right. 0:19:34.160 --> 0:19:37.080 It's not like the rays of light all converge into 0:19:37.200 --> 0:19:40.400 a point of space and then just create a point 0:19:40.440 --> 0:19:43.840 of light. Those rays will continue on in a straight line. 0:19:44.280 --> 0:19:48.080 So now they're diverging from one another. They keep on 0:19:48.119 --> 0:19:51.080 going until they hit something and they reflect off of it. 0:19:52.160 --> 0:19:54.840 So the objective lens faces out into the world, and 0:19:54.880 --> 0:19:59.320 the other lens is the eyepiece or ocular lens, and 0:19:59.400 --> 0:20:04.760 that magnifies that light from within the telescope and spread 0:20:04.800 --> 0:20:06.560 it out so that that light takes up more of 0:20:06.560 --> 0:20:10.200 the space on your retina. So these diverging rays hit 0:20:10.280 --> 0:20:13.840 that second lens. That second lens then bends the light 0:20:13.880 --> 0:20:15.720 in a way that directs it towards the eye of 0:20:15.760 --> 0:20:18.720 the person using the telescope in a in a parallel fashion, 0:20:18.800 --> 0:20:23.719 So it returns the light to a parallel alignment. So 0:20:23.760 --> 0:20:25.959 what you view through that eye piece is a virtual 0:20:26.040 --> 0:20:30.160 representation of the real thing that the objective lens has 0:20:30.200 --> 0:20:33.159 in focus. And this virtual object is much closer to 0:20:33.200 --> 0:20:36.120 your eye than the real object is, so you get 0:20:36.119 --> 0:20:40.040 the effective magnification lipatis. Early telescopes can magnify stuff to 0:20:40.080 --> 0:20:43.320 about three times their relative size to the viewer's perspective, 0:20:43.760 --> 0:20:47.720 so not incredible, but an improvement. One interesting point about 0:20:47.760 --> 0:20:51.280 this type of telescope if we were talking specifically about 0:20:51.359 --> 0:20:55.919 using convex lenses on both the objective lens and the 0:20:55.960 --> 0:20:58.800 ocular lens, the eye piece lens or the optical lens, 0:20:58.800 --> 0:21:01.440 if you prefer if you're using both of those as 0:21:01.480 --> 0:21:04.960 convex lenses, and you're you've got the focal point inside 0:21:05.160 --> 0:21:09.200 the telescope itself, the second lenses behind that focal point. 0:21:09.880 --> 0:21:12.680 As the light converges and then diverges within the telescope, 0:21:12.720 --> 0:21:15.880 the image flips upside down. So if you draw this out, 0:21:16.000 --> 0:21:19.119 it all makes sense. The light rays are coming from 0:21:19.680 --> 0:21:24.080 the outside world, right, and the light rays that are 0:21:24.080 --> 0:21:27.680 on the top if you think of it in respect 0:21:27.680 --> 0:21:29.800 of the telescope, the top of the telescope part, and 0:21:29.880 --> 0:21:32.960 you're looking at a cross section of it, they get 0:21:33.000 --> 0:21:36.159 bent so that they aimed downward relative to the telescope. 0:21:36.480 --> 0:21:39.320 The light rays coming from the bottom side of the lens, 0:21:39.600 --> 0:21:44.159 for example, then get bent upward with respect to the telescope, 0:21:44.400 --> 0:21:46.320 and then they continue on their journey. They hit that 0:21:46.480 --> 0:21:49.960 focal point and they keep going in a straight line. Uh. 0:21:50.000 --> 0:21:53.800 And so the light that was at the bottom of 0:21:53.840 --> 0:21:57.640 the objective lenses at the top of the optical lens 0:21:57.720 --> 0:22:00.159 or the the ocular lens. The light that was the 0:22:00.200 --> 0:22:02.520 top of the objective lens is at the bottom of 0:22:02.560 --> 0:22:05.560 the I piece lens. So that's why if you were 0:22:05.600 --> 0:22:08.080 looking through such a telescope, the object you were looking 0:22:08.119 --> 0:22:12.720 at would be upside down. Uh. If we use such 0:22:12.720 --> 0:22:15.359 a telescope to look at a celestial body, that's not 0:22:15.400 --> 0:22:18.320 a big deal because top and bottom in space is 0:22:18.400 --> 0:22:21.119 largely unimportant. If we wanted to use it in a 0:22:21.240 --> 0:22:23.879 terrestrial sense, like you wanted to use the telescope to 0:22:24.000 --> 0:22:27.920 look at stuff around you on Earth, Like let's say 0:22:27.960 --> 0:22:30.240 that you have a spyglass and you're a pirate, then 0:22:30.320 --> 0:22:32.440 looking at a distant object might be a bit of 0:22:32.440 --> 0:22:34.560 a surprise because it would suddenly be flipped upside down. 0:22:34.880 --> 0:22:38.560 Modern telescopes use stuff like prisms and mirrors to correct 0:22:38.560 --> 0:22:42.879 for that vertical inversion. They're called erectors. But what about 0:22:43.000 --> 0:22:48.080 old telescopes before we figured that out? We're all those 0:22:48.080 --> 0:22:51.720 pirates we see in romanticized movies looking at stuff upside 0:22:51.760 --> 0:22:55.600 down the whole time. Well no, so, while my description 0:22:55.640 --> 0:22:58.920 of objective lenses and eyepieces and all that sort of 0:22:58.920 --> 0:23:02.800 stuff is accurate. From modern refracting telescopes, the type used 0:23:02.840 --> 0:23:08.000 by astronomers and seafarers from around oh say, sixteen ten 0:23:08.200 --> 0:23:12.719 to about sixteen seventy or so followed the Galilean method. 0:23:13.119 --> 0:23:18.520 Galileo began using telescopes for astronomical observations not long after 0:23:18.640 --> 0:23:23.359 Liberacy's work became widely known. So like by six ten, Galileo, 0:23:23.640 --> 0:23:26.920 like Libacy, used a convex lens as the objective lens, 0:23:27.320 --> 0:23:30.840 and a concave or diverging or negative lens as the 0:23:30.880 --> 0:23:33.960 eye piece lens. So like coming in through the objective 0:23:34.040 --> 0:23:38.680 lens would bend inward towards a focal point, the diverging 0:23:38.800 --> 0:23:42.040 lens would reverse the direction of the bend before the 0:23:42.119 --> 0:23:44.760 rays could hit the user's eye, so the top and 0:23:44.880 --> 0:23:49.520 bottom wouldn't switch, everything would still be in the proper alignment. 0:23:49.880 --> 0:23:53.080 As the Institute and Museum of the History of Science 0:23:53.119 --> 0:23:56.439 puts it, quote, the eye piece is situated in front 0:23:56.520 --> 0:23:59.680 of the focal point of the objective at a distance 0:23:59.720 --> 0:24:02.879 from the focal point equal to the focal length of 0:24:02.920 --> 0:24:06.400 the eye piece end quote. That gets a little confusing, 0:24:06.440 --> 0:24:08.080 but if you were to draw it out, it makes 0:24:08.119 --> 0:24:11.639 a lot of sense. You would have the convex objective 0:24:11.720 --> 0:24:14.520 lens at the front of the telescope. Lights coming from 0:24:14.600 --> 0:24:18.359 outside world in parallel rays. It hits that lens and 0:24:18.400 --> 0:24:21.200