today we're going to continue talking about light specifically last time we talked about all the different kinds of light right over the last few times but what we're going to be talking about today is now what can the light tell you okay well if we look at an object other than just being able to see it what can we learn about that object based on the light that's coming to us especially if we use all of these invisible types of light to help give us even more information okay so here's how here's specifically what we're going to be learning so three things the spectrum can tell us okay and there's a whole bunch of information we can learn about objects out there but we're gonna be learning three major things in this chapter and that's the last three things that we're going to learn about before the first test okay so we'll see how long this takes us alright so first up before we can even talk about what the three things are we need to know what is a spectrum okay so let's talk about what a spectrum is and then we'll come back and start talking about the three things that it can tell us okay so we just kind of scoot this over for a second let's figure out what a spectrum is let me put it in words first a spectrum is just a fancy way to say the pattern of light that an object gives off okay a spectrum is the pattern of light an object gives off okay and that might be kind of vague okay so let me show you one of the ways that you can show the spectrum of an object the most commonly used way is a graph okay so let's just draw a really quick graph real quick just a normal old graph okay and on this graph on the x-axis we have this okay does anybody remember what that symbol stands for does anybody know let me zoom in a little bit here does anybody remember what this symbol right here stands for we talked about it over the past few times so that it's called lambda but what concept does it stand for wavelength wavelength that's correct wavelength is what it stands for okay so on this axis down here we have wavelength increasing in that direction okay we have wavelength increasing in that direction so big wave links are on the right small wave links are on the left so here's my question where would radio light be on this graph would radio graph would radio light be in the middle on the left or on the right that's your choices where would radio be okay and remember wavelength is increasing as you go to the right you have to think of the size of the wavelength of radio light okay it would be on the right that's correct it would be on the right and that's because remember radio light was the longest kind of light so radio would be over here visible would be in the middle of the graph and then gamma rays would be way over here on the smallest wavelengths remember longer wavelengths mean lower energies shorter wavelengths mean higher energies so radios on the right gammas on the left and everything else is in between okay now on this axis we have something I'm gonna label with a capital I and that just stands for intensity okay intensity basically brightness right so this is basically a graph that tells you how bright every wavelength is from that object okay so a spectrum you can think of it as a a graph of intensity of every wavelength of that object so the brighter like if an object was giving off a lot of gamma rays this part of the graph would be really tall if it was giving off a lot of radio this part would be really tall and if it was giving off a lot of visible the middle would be really tall okay so typically a typical object might have a spectrum that looks like this sort of a single hill shape okay so this particular object this one right here that I just drew if this was what the graph looked like here's my question is this object giving off a lot of gamma rays is this object right here giving off a lot of gamma rays yes or no and if it's if it's giving off a lot of gamma rays the intensity would be really high in the gamma region right so no that's correct no this one is not giving off a lot of gamma rays because the gamma part of the graph has a very low intensity it's also not giving off a lot of radio okay but this particular object is giving off at least a little bit of every type of wavelength that there is at least a little bit right yeah okay so keep that in mind but here's where I should go there's actually only one type of object that makes a spectrum that's a perfect single hill like this okay and we can think of that as a perfect light okay an absolutely perfect light will give off at least a little bit of every type of wavelength not necessarily in the same amount but at least a little bit of everything okay and of course we get a freeze already oh we're off to a good start and I'm bringing that up because this is not the only way that you can show a spectrum okay this is not the only way that you can show a spectrum to help you understand what I'm trying to talk about right here let me explain how we get the spectrum oh so this has that's a very good question someone is asking is this graph for one specific light or all light that we know so this is the spectrum of one object where we have split the light into all of the color all of the wavelengths that that object is giving off okay and we put it on a graph of all known wavelengths and if that particular object was giving off a lot of gamma rays then when we when we pick up the gamma rays this part of the graph would show very high so this is the spectrum is of an object and this graph is just telling us which wavelengths it's giving off and how bright each one is okay and how do we do that when we look at an object you don't just see one wavelength at a time you see everything mixed together right you see everything mixed together so in order to make this graph what we have to do is we have to take the light that that object's giving off and split it so that we can see how bright each one is okay so let me just show you a picture from the book real quick this will help explain what I'm trying to say this is not the picture I wanted this is the picture I wanted so right here imagine that this right here is a perfect light okay imagine that's a perfect light one way that we can split the light is by passing it through a prism or a little piece of glass like this and that's gonna cause all of the different colors to bend different amounts does it might remember what that's called does anybody remember what this this process is called when we take that light and bend it take that light and bend it through a substance that one we've seen a few times now yeah that's refraction that's refraction so what we can do because we don't want all of the light to be mixed together we can refract that light or do other processes that do basically the same thing and because every color in that original light bends a different amount you're gonna end up splitting that light into essentially a rainbow alright so if this is a perfect light source then that complete rainbow will be present right if it's not perfect like let's say this object didn't have any yellow light in it when we split it into this rainbow then the yellow right here would just be black it would be missing right so only a perfect light source produces a perfect rainbow and right here this is another way to show the spectrum of that object this is actually what the photograph of the spectrum actually looks like when we actually take the data so if this object for example was giving off way more red than the other colors then the red part would be the brightest part of the rainbow so that means this picture is telling us how bright each wavelength is right and what they've done here is they've taken this rainbow photograph and turned it into a graph like I was talking about just a second ago see wavelength versus intensity so both of these are two ways to show the spectrum of an object and we can actually extend it into the invisible types of light in both directions if we have a good camera okay so here we go if you have an absolutely perfect light source that has every single color present including all the invisible ones then your graph is gonna be nice and smooth okay like the ones I've been drawing and if that's the case we call that kind of spectrum a continuous spectrum okay a continuous spectrum so the only type of object that actually makes a perfectly smooth continuous spectrum is a perfect light source okay now here's my question when we look at objects out in space how many of them are probably perfect how many of the objects in space are probably perfect light sources if you were to guess yeah very few none is actually the correct answer that's none so basically nothing is ever going to make an actual perfect rainbow there's always gonna be something missing in every natural object so continuous spectrums are kind of like the ideal that we compare things to but we never actually see them we actually see two other kinds of spectrum which we'll talk about in a little bit okay so that's the basics on what a spectrum is okay it's just a graph it's just a way to display how bright every color is coming from an object so what we're gonna be learning today is what can we learn about the original object based on the shape of this okay