Full transcript
0:00there is one more type of spectrum to
0:02consider that is the so called
0:04absorption spectrum and you can see it
0:07looks like a continuous spectrum but
0:09there's certain lines missing well what
0:14happens is if we have that hot dense gas
0:16like Arzo giving off this emission
0:21spectrum and we'd normally be expecting
0:23a continuous spectrum but if there is a
0:25cool gas between us that cool gas will
0:31actually absorb some of these lines and
0:34the weird thing is or maybe not weird
0:37depending on what do you think the lines
0:39that it absorbs would be the exact same
0:42ones that gas would emit if it was
0:44heated up so let's go back a second if
0:48we took a gas cloud of sodium put it in
0:51between us and continuous spectrum these
0:54lines that it would emit if heated are
0:56the exact same lines it would absorb
0:59exact same ones and now again this is
1:05pretty useful already if we can look and
1:08get the absorption spectrum of something
1:11we can tell and if it should be a
1:12continuous spectrum but there's a cloud
1:15between us we can tell what that gas
1:17cloud is made up of by which lines it
1:19absorbed and actually let's say it's
1:22made up of multiple elements
1:23it'll just be all of those lines for the
1:26different elements that will be absorbed
1:27so even if this gas cloud is made up of
1:29many different elements we can determine
1:31all of the elements within it so we can
1:34start using this to figure out the
1:36composition of different things and when
1:39you think about it now we have light
1:41coming from a distant object and we can
1:43figure out what that object is made up
1:46of that distant star run it through a
1:49spectroscope we can figure out well
1:52maybe not distance orizari because it'd
1:54be a continuous spectrum but if we had a
1:56gas cloud that was off to it at a
1:58distance and was heated up and giving
2:00off an emission spectra we could
2:02determine what is made up of if we had
2:06some source like a star giving off
2:09continuous spectrum but there was
2:10something in between us in it we could
2:12determine what
2:13thing is made up of by looking at the
2:15absorption spectra what lines are
2:17missing would tell us what elements that
2:19object has in it so already now we've
2:23seen we can figure out the temperature
2:25of distant object now we can figure out
2:26what is made up of and we see this in
2:31our Sun this is the very detailed
2:35absorption spectrum of our Sun and you
2:37can see it should be we'd expect a
2:40continuous spectrum but there's many
2:41many lines missing what this means is
2:45this is actually the outer surface of
2:49our Sun the outer cooler gas surrounding
2:52our Sun so when I said technically you
2:54wouldn't figure out what a star is made
2:56up of actually we would I just was kind
2:59of holding back a bit because the outer
3:02portion of the Sun does absorb some of
3:05those lines so we're getting an
3:08absorption spectrum and that's because
3:11the outer layers of Sun absorb some of
3:13these so if we know the outer layers of
3:16the Sun we can assume it's similar to
3:19the other layers of the Sun and thus
3:22determine the composition of our Sun or
3:24of a distance start by looking at the
3:26absorption spectrum we figure out what
3:29something is made of and actually it's
3:32worth noting that when they first
3:33started doing this they actually
3:35identified an element in the Sun before
3:38we ever found it on earth good old
3:40helium helium was found in the Sun
3:43before it was discovered on earth
3:45because we noticed the absorption lines
3:47had no idea what it was it wasn't one of
3:50the elements we had identified in lab
3:51they eventually found it on earth as
3:53well