this kind of spectrum the absorption line spectrum is made when this gas absorbs some of the wavelengths out of a beam of light but that's not super helpful all the time for a lot of clouds of gas because here's the thing where are the clouds of gas that we're studying in astronomy where are these clouds of gas where are they don't overthink it are they in this room so that I could put a light bulb behind them no they're in space so can I go behind the cloud of mystery gas and set up a light bulb if the mystery gas is in space no so we can't set this up in space most of the time if we're lucky a star will go behind the cloud of gas we're looking at and we can try to use the star as the close to perfect light source and get an absorption spectrum off of it but that doesn't always happen so what do we do when the mystery cloud is just by itself well chances are every gas that we're looking at in space is has stars nearby so they've those gases out there have absorbed light from nearby stars but let me go back to my picture of an atom when an electron pops up does it want to stay up does the electron want to stay up when it goes up no it wants to come back down right it wants to come back down and here's the kicker if it took in light to pop up when that electron falls back down what happens let me ask that that's that's that's the next question if the electron took in light to pop up what's gonna happen when that electron pops back down don't overthink it if light came in to pop it up that means there's stored energy in here yeah when those electrons fall back down which is what they want to do any light they stole to pop up they're gonna give right back off to pop back down okay so that means this check this out let me go back to that book picture if we have this perfect light on this gas this gas is getting pumped up by stealing light there's the stolen wavelengths right but let's say we turned this light off let's say we turned it off now the gas cloud isn't stealing light anymore and it doesn't want to have its electrons up so it's the light its stole it's like you know what I didn't even want this I didn't even want this stuff I stole so it lets its electrons fall back down at any gas that guts there's like any light that got stuck in here will then come out but ah here we go whoo but uh if we look at the light that comes out of this gas once we turn let me block this light with my head once we've turned this light off we'll every wavelength come out of this gas will we expect when we see the light coming out of this gas will this gas give off all wavelengths yes or no will it give off all possible wavelengths no it's only gonna give off what it stole so even if there isn't a light behind the gas it's always gonna steal light from nearby light sources but it doesn't want to hold on to them so if you look at just the gas without the light then you're gonna see it giving off its stolen goods right so in other words if we turn this light off how would we expect this this picture to change over here well the rainbow colors right here those were coming from the light so when we turn that light off all of those will go dark but because the gas wants to give off what its stole it will give off the colors that were missing so what will happen to this rainbow what would this rainbow look like if we switch the situation it'll go from this to this so when the lights on you see what the gas stole but when you turn that light off you only see the stolen goods does that make sense so most of the rainbow is missing because we turned off that light so this gas just by itself will only give off the things it stole from nearby lights okay and so this kind of spectrum looks totally different from the other kinds of spectrum and when we turn it into a graph see how we don't really have that Hill anymore we just have these sticks this kind of spectrum is called an emission line spectrum because now we're seeing what the gas emits instead of what it absorbs so let me just go through those real quick if you've got an absolutely perfect light source it's gonna make a continuous spectrum which is a perfectly smooth graph continuous spectrum if you put a gas in the way it will absorb some of the wavelengths and so you've got a rainbow with a few colors missing or a perfect curved graph with a few colors missing that's the absorption line spectrum but if you then get rid of the light source and just look at the gas it will give off its stolen goods and give you an emission line spectrum which is mostly dark with a with just a few colors okay and again we can tell what this gas is made out of by the pattern we see over here because the same gas that absorbs this pattern basically makes just the inverted pattern when it's giving it off so either one of those the absorption or emission spectrum can both tell us what something is made out of okay let me give you guys some examples just a couple of questions and this is all we're gonna talk about today so here we go finish it up so what kind of spectrum is this what kind of spectrum is this right here is this a continuous spectrum absorption or emission give me one of those three this is emission okay how about this one what's this one right here is this continuous absorption or emission absorption so you should be able to identify what kind of spectrum you're looking at and again this right here I actually showed a second ago I said that was the absorption spectrum of hydrogen so can anybody tell me what element this is the emission spectrum of this is the absorption spectrum of hydrogen what element makes this emission spectrum hydrogen and how can you tell how can you tell that this is also hydrogen because the pattern is the same right just invert it because the pattern is the same just in