Full transcript
0:00great so we have all of this light we've
0:03collected all this light our telescope
0:05we've brought it to a focus and sent it
0:07somewhere but now what what do we do
0:11with it well this is where those other
0:13two pieces of our electromagnetic
0:17radiation detecting device come in we
0:19had our telescope and then remember the
0:22second part was possibly sorting it
0:25based on a certain wavelength it's
0:27possible we're not interested in all the
0:29wavelengths maybe we want to study one
0:30in particular also ideally we want to
0:34detect it we need some kind of detector
0:37to actually take that in the signal
0:39we've got that focused light and do
0:42something with it
0:43well early on the detectors were simply
0:46the human eye remember and we had
0:49telescopes get invented about 1608 and
0:52good old Galileo heard about this and
0:54built his own telescope and actually
0:57looked at the sky and started observing
0:59things well all he had was his eye so he
1:02had to observe that and then write about
1:04his observations not the most perfect
1:07record to keep because it depends on hey
1:09how good you are at actually taking that
1:11and translating it to paper if he's not
1:14a great artist we're gonna be in trouble
1:16so we wanted to build to better and
1:18better types of detectors and the next
1:21real advancement was the idea of using
1:24photographic plates was taking light and
1:27actually trying to make a photograph of
1:29the light captured trying to get an
1:31image of what it is that we were looking
1:34at but really it was I mean a huge
1:38improvement over someone drawing in a
1:40book but it was still very poor in many
1:43ways the images were good a lot of the
1:46light was wasted in fact I believe is
1:48something about 1% of the light that was
1:50collected actually went into making the
1:53image so very very incredibly
1:57inefficient way of taking the light and
2:00actually trying to create something out
2:02of it nowadays we have a much better
2:05device so-called charge-coupled devices
2:09charge-coupled devices or CCDs for short
2:13great these actually have the light
2:16again we've focused it somewhere maybe
2:18to the base of telescope maybe to a
2:20specific room but what we have is the
2:22light hit this device it hits these
2:26charge-coupled devices and what happens
2:29is you can see this is a much smaller
2:30image it shows many many charge-coupled
2:32devices actually but this eye actually
2:35shows a smaller image and within it what
2:38we have is many many little pixels
2:41basically in fact millions of pixels in
2:45many cases and millions of pixels or
2:48otherwise known as megapixels hopefully
2:51that a term sounds familiar a megapixel
2:54probably when you buy your cell phone
2:56you looked at the megapixels on the
2:59camera well this is a very similar idea
3:03what we have is these pixels within our
3:06cccd in our telescope or within your
3:09camera what is happening is we're
3:11capturing light to make an image so all
3:15of these little tiny dots these are
3:17pixels and what they're gonna do is
3:20capture photons little dots of light so
3:24each of these photons is gonna capture
3:25light and basically is gonna act as a
3:28counter oh one photon hit here and then
3:31one photon hit over here oh another
3:34photon head here and it's counting how
3:35many photons of light hit this specific
3:38point and from that you can reproduce an
3:41image as these are incredibly small
3:45millionths again of pixels on something
3:48as small as this like look at the scale
3:50of this person's thumb compared to this
3:52device and yet there's millions of
3:53pixels are mega pixels each one counting
3:58light and from the number of photons the
4:01more photons the brighter the light at
4:03that specific point and what we end up
4:05doing is getting a digital image this is
4:08the same basic idea in your phone pixels
4:11of light coming in and we can actually
4:13figure out how to reproduce the image
4:16and we now have a digital image so much
4:19better than any of the other options
4:21we've had up till now again the
4:23photographer graphic plate very
4:25inefficient the
4:26you can capture most of the photons
4:28depending on the actual CCD you're using
4:32it might be say 60 70 percent some of
4:35them I believe can get up to about 90
4:37percent either way we're capturing a lot
4:40more of the light and using it so that's
4:43much better images if we're wasting
4:46light we don't get a good image
4:48if we capture most of it we're gonna get
4:50a very clear image and the idea of
4:52having a digital image is where the
4:54power comes in because sure capturing a
4:58photographic image is better than a
5:02human eye but it's not the most useful a
5:05digital image can be shared can be
5:08cleaned up using digital processing -
5:10theoretically but we can also share it
5:12and so one telescope
5:14all of a sudden produces images that are
5:16used by researchers around the world I
5:19mean you go to NASA you see many of
5:21these images shared freely for people to
5:23see so we can end off Sun take those
5:26images and use them for a variety of
5:29purposes also I mean we have a digital
5:31count of all the photons it doesn't have
5:33to just be for a digital image what
5:36often is done is still that good old
5:38spectroscopic analysis taking the light
5:42splitting it into its component covers
5:46now this figure probably looks pretty
5:49complicated but all we're doing is the
5:51lights focus to a point and then we're
5:53gonna take that light put it through in
5:55essence a prism it might be a grading or
5:58something but the idea is we're taking
6:00that light and splitting it into its
6:02component colors and then each of those
6:04component colors it can be sent on to a
6:07CCD so we can actually split it into the
6:10different colors and still get many
6:12different images and have study at at
6:14different wavelengths and do
6:15spectroscopic analysis where we start
6:17determining things like the temperature
6:19what is made of is it moving towards us
6:23or away and how fast so those analyses
6:25that we looked at in the previous
6:27chapter and also maybe against really
6:30cool digital images all at the same time
6:33so we're still using a CCD it's just
6:36maybe we have C CDs that one's going to
6:38be detecting
6:40one green one violet so this is actually
6:44one of the most common things we do in
6:46astronomy as it says here more than half
6:49of the time spent on most large
6:51telescopes used for spectroscopy because
6:53as we saw a last chapter we get a wealth
6:55of information be able to tell what
6:57something is made of and how hot it is
7:00and if it's moving towards us that's
7:02quite a bit of information