Full transcript
0:00now
0:01this again we've really been talking
0:03mostly about visible light we're
0:04capturing visible light but this same
0:07basic setup
0:08should work for infrared as well these
0:10same types of mirrors the infrared rays
0:13would bounce off the infrared mirrors
0:15and would actually be focused to a point
0:17and still collected on a ccd they would
0:20be using a different ccd that's
0:22sensitive to infrared radiation and
0:24captures those photons but the basic
0:26setup that we've been talking about is
0:28the same which is nice useful i mean we
0:32haven't really had to change our
0:33thinking
0:35but there is a pretty big complication
0:39we talked
0:41previously about the idea that infrared
0:44is given off by objects of our
0:46temperature as this image shows this is
0:48this person radiating off in infrared
0:51part of the spectrum you can even see
0:52the hands through the bag because he's
0:55giving off infrared
0:56radiation well
0:58this poses a pretty big problem a lot of
1:01objects near us
1:03give off infrared radiation
1:06things at in around these temperatures
1:08are giving off infrared radiation many
1:10of the things near the telescope some of
1:12the actual pieces of the telescope can
1:14give off infrared radiation it's hard to
1:16take an image of infrared radiation when
1:19everything's giving it off it'd be like
1:21trying to take a visible
1:24image of the stars during the day
1:26there's so much light it's getting
1:28washed out well that's what we're trying
1:30to avoid in infrared getting all that
1:32radiation from the sky washed out by
1:35things nearby on earth
1:37and so what we have to end up doing is
1:39cooling things down we actually have to
1:42cool down the infrared telescopes so
1:45they're not in for giving off infrared
1:47radiation themselves
1:50and of course we can't be standing near
1:51it we can't be right in front of the
1:52thing going what's that oh darn i just
1:54ruined this major beautiful image no we
1:57cool down this telescope and what they
1:59actually often do is things like liquid
2:01helium they actually use liquid helium
2:04to cool down these infrared telescopes
2:06down to
2:07about only a couple kelvin incredibly
2:11incredibly cold
2:13over negative 260 degrees celsius to
2:17give you an idea
2:19and give you a basis of comparison so
2:22incredibly cold because otherwise again
2:24the light from stars will be washed out
2:26by the infrared nearby
2:29setup is the same except we'd better
2:31make it a lot cooler and we'll talk
2:33about some other
2:35methods in a little bit too
2:37we've looked at telescopes for visible
2:39light and saw that they also tend to
2:41work for infrared part of the spectrum
2:43as well
2:44but if we start looking at radio waves
2:47we need to come up with radio telescopes
2:50and this was discovered almost by
2:52accident really it was about 1930s
2:54someone working at bella laboratories
2:56they were using antennas
2:59and they noticed they were getting this
3:01mysterious weird static this extra noise
3:04this
3:05annoying static
3:07and the weird thing is it started
3:09happening four minutes earlier every day
3:13and hopefully that sounds a little
3:14familiar think back remember sidereel
3:16day is four minutes shorter than the
3:18solar day so if something's happening
3:20four minutes earlier every day it means
3:23it's likely coming from
3:25the same portion of the sky they
3:27realized this was something from space
3:29they were observing radio waves from
3:32space and remember this is an
3:33electromagnetic radiation
3:36and what they realized is that this
3:38was causing
3:40an actual current in the antennas they
3:42were using and thus really radio
3:45astronomy was born we could detect the
3:48radio waves from space
3:51okay
3:52so what does it look like well the
3:54setups actually look a lot like this
3:56kind of like your good old satellite
3:58dish
3:59there's a big dish
4:00and uh
4:02something at the top
4:03a detector
4:05and what we're doing is using the dish
4:06to focus the beams to a certain point
4:09right up here so it looks a lot like
4:11again a normal satellite dish
4:14and of course
4:16there's a few things to keep in mind
4:18because it's not quite the same setup as
4:20with visible light it even though it
4:22looks a little bit like a prime focus
4:24for one thing we can look over here and
4:26look at some of the different radio ones
4:28out there and one thing you might notice
4:30right off the bat is they are big
4:33look at this one 305 meters 100 meters
4:3576 meters that's quite a bit bigger than
4:38the visible telescope we were talking
4:40about and the thing is
4:42we can build them bigger
4:44radio telescopes are less sensitive to
4:48imperfections the wavelengths of radio
4:50waves are much larger so they're not as
4:52easily deflected in the case of a mirror
4:55tiny little cracks that's going to send
4:57visible light flying but for radio waves
4:59they're much less sensitive to
5:01imperfections so our satellite dishes or
5:04radio dishes sorry can be built much
5:06larger because imperfections aren't as
5:08big a deal in fact this one up here this
5:11big 305 meter dish it's actually kind of
5:15really cool it's built into a mountain
5:18and that means of course it can't be
5:20rotated or moved really it's just in a
5:23fixed spot it's this huge one built in
5:25the mountains and the thing is they
5:27initially built it basically with
5:29chicken wire and like huge cables and
5:32like it but the idea was that was enough
5:35even though there was gaps between the
5:37wires they were small enough that the
5:40radio waves could still be focused so
5:42it's much less sensitive to big
5:45imperfections so we can build them
5:46larger
5:48which is good because we need to build
5:49them larger remember diffraction causes
5:53the resolution to be
5:55poorer in radio telescopes we get worse
5:59images so we need larger
6:02radio telescopes to get any kind of
6:04decent image because otherwise the
6:06resolution tends to be very poor
6:08remember it depends on the size of the
6:10telescope and wavelength since the
6:12wavelength is much larger in radio
6:14telescopes the size must be bigger to
6:17compensate for this poor quality we
6:19would get
6:21thing is radio telescopes does have some
6:24advantages when we're studying radio
6:26part of the spectrum
6:27we don't need to wait for night
6:29visible you really need to wait till
6:31it's night to be able to see the stars
6:33because you can't see them with your eye
6:35so neither can a visible telescope
6:37well
6:38except obviously at night sorry during
6:40the day you wouldn't be able to see them
6:41with your human eye but
6:43neither would a telescope so we wait
6:45till night radio telescopes so they can
6:47study all day long in fact even clouds
6:50don't generally cause a problem even
6:52rain
6:53so we can make observations
6:56generally 24 hours a day
6:59also though it's just important to study
7:01an entire different part of the spectrum
7:03can't stress this enough if we don't
7:06look at the other parts of the spectrum
7:07we literally will miss things this is a
7:09radio image you can see it's made like
7:11the colors look weird that's because
7:14obviously the radio image doesn't have
7:16colors that they're not part of the
7:18visible spectrum so what we use is false
7:21colors we make colors to mean certain
7:23things
7:24more intensity of light normally or more
7:26intensity sorry of radiation of the
7:28radio waves so these big huge clouds are
7:32things we would have missed
7:34what we have is that dot right there a
7:36galaxy
7:38think about that that's a galaxy and if
7:41we're looking at visible light that
7:42would be the spectacular amazing thing
7:43we were studying but it's a tiny dot
7:46compared to these huge massive clouds
7:50that are identified by the radio part
7:51spectrum and we would otherwise not even
7:53know they existed
7:55very important to study different parts
7:56of the spectrum