Full transcript
0:00now there is generally three main types
0:02of telescopes we're gonna talk about
0:04them a little more but the idea of a
0:06refractor a reflector or kind of a
0:10hybrid of the two a compound which we're
0:12not really gonna talk about the compound
0:13telescope but we're gonna focus on these
0:16refractor and reflector types remember
0:20though we're trying to gather as much
0:21light or radiation as possible and
0:24ideally bring it to a focus so that's
0:27the important thing to keep in mind here
0:31how do we do that well in the case of a
0:37refractor light is actually refracting
0:41through a lens in a case of a reflector
0:46light is reflecting off a mirror so the
0:49names kind of make sense it is important
0:51to remember that we're looking at
0:53objects that are very very far away and
0:56that means the light coming from them
0:58are in essence parallel light rays now
1:01we talked about this in a previous
1:03chapter we talked about how our Sun we
1:05could basically approximate the Rays
1:08coming from it as parallel when we're
1:10looking at things are even further the
1:12light rays really are parallel because
1:13any that didn't start off parallel would
1:16miss us so if the light rays coming from
1:19something hit us and hit even a
1:21relatively large telescope well any
1:24other rays coming in must also be
1:26parallel to those ones because they came
1:29from so far away like this image shows
1:31they would miss us if they were even a
1:34little bit off from being parallel to
1:36each other okay now why is the idea of
1:39parallel light rays important that
1:41relates to the idea of focusing the
1:43light rays remember when we looked at
1:46spectroscopy we saw a light passing
1:48through one medium will Bend well the
1:52light going through a lens will be bent
1:55and focused to a specific point I have
1:59so called focal point at a certain focal
2:02length from the lens I mean not the most
2:04creative names with very apt
2:05descriptions it gets focused to a point
2:07and that's where you get your clear
2:10image so that's the idea of the focus
2:12we're getting a clear
2:13image because of light rays from this
2:15distant object are getting focused to
2:18that point that's where you get your
2:19image in the case of the mirror the
2:21light actually rebounds or reflects off
2:25of the mirror and is also focused to the
2:28focal point at a certain poco length so
2:31the ideas are the same it's just in this
2:33case it's refracting through the lens in
2:35this case it's reflecting off the mirror
2:38which we will see has some important
2:40consequences but the over idea is still
2:42the same light comes in gets focused to
2:45a point because we have these parallel
2:47light rays that being said you might be
2:51asking yourself how do we get an image
2:54then for getting an image like how do we
2:57get an image if all the light is being
2:58focused to a point isn't it all just
3:00blur it on top of each other well we've
3:03added we had a bit of a simplification
3:05in a previous slide we talked about all
3:06the light rays being parallel well
3:09technically the object we're looking at
3:11is not just a dot necessarily I mean
3:14even when we see a star to us it looks
3:16like a dot but technically the light
3:18coming from the top and the light coming
3:19from the bottom will come in at slightly
3:21different angles and of course we're
3:23looking at something even closer the
3:25light gets from the top and the bottom
3:27is different and so this has a nice
3:30demonstration if you're looking at these
3:31rocks the light from this top rock comes
3:34in a slightly different angle than the
3:36light from the bottom Rock and thus
3:38those different rays actually get
3:40focused different the light from the
3:42bottom rock is still parallel to the
3:45rest of the life on the bottom rock so
3:47it all gets focused to a specific point
3:49but the light from the top Rock is gonna
3:51be focused to a different point because
3:53it's at a slightly different angle to
3:55this so light rays from the same thing
3:58are parallel but when you're comparing
4:00the top of an object to the bottom
4:02there's slightly different angles and
4:04gets focused slightly different and so
4:07this is a long way of saying we get an
4:09image it still produces an image just
4:12because each part gets focused to a
4:13slightly different part which is related
4:15to what we were seeing and thus we get
4:17an image one of the odd things though is
4:21that the image will actually be flipped
4:22because of the characteristics of optics
4:25the image would be flipped
4:26and the same basic idea is happening in
4:29our eyes not as this image shows this is
4:32a mirror and it's reflecting but when we
4:34were thought about the previous slide
4:36where shows a refractor with the lights
4:38going through a lens and being focused
4:40well that's what happens with your eyes
4:41your eye is just a lens same with your
4:45glasses if you use glasses your glasses
4:47are just helping focus the light to a
4:49specific point if there's your lens in
4:52your eyes doesn't quite focus it
4:54properly to the right place to be read
4:56and thus you get a blurry image but the
4:58lens in the glasses will help focus it
5:01so that it does actually end up at the
5:03right part and so you can actually see
5:06it but it is kind of funny that it does
5:08get inverted and our brain just flips it
5:11for us so we end up with an image of
5:14whatever we are looking at now again
5:20this show is a basic setup of the
5:22refractor and reflector telescopes what
5:25we have is the light coming in and
5:28either refracting through a lens or
5:31reflecting off the mirror but the thing
5:35is we don't often just stop there what
5:39we want is the image to actually be hot
5:43summer to be viewable in the case of
5:45amateur telescopes usually there's an
5:47eyepiece we want to be able to actually
5:48see a copy of this image at the eyepiece
5:51and so the light even though it might be
5:54focused to a point often what will
5:56happen is it'll be either deflected out
6:00an eyepiece or yeah maybe by secondary
6:03mirror or it just goes to the eyepiece
6:07here in the refractor case the main idea
6:09is we want to be able to actually put
6:10our eye there and see the actual image
6:14because otherwise if it's just focused
6:17within the me and the actual telescope
6:19well great you can't see that and in
6:21this case if it was focused here sure if
6:25you had a nice beautiful image but you
6:26couldn't see it wouldn't be helpful so
6:28often what we actually have is a
6:29secondary mirror that will deflect it to
6:32an eyepiece or other situations and
6:35allude to in a second but one of the
6:38advantages of telescopes right now
6:40again we get this nice focused image we
6:43can see it but many modern telescopes
6:45have a variety of eyepieces that come
6:47with them as well and the thing is each
6:50of these eyepieces allow a slightly
6:52different magnification we have the
6:54light coming in from our image we get
6:56our image and it's focused to a point
6:57but the size the magnification of that
7:00image can be modified by the eyepieces
7:03so when you actually view it so often
7:06with amateur telescopes you're gonna see
7:08they come with a variety of eyepieces so
7:10you can see it at different
7:12magnifications