 Greetings and welcome to the Introduction to Astronomy. In this video we are going to look at the black body curves and UBV filters lab and look at the some of the material that you need there. Now there is some background material for you to look at in terms of spectra and filters and even the color index to learn a little more about that. But what we're going to look at here are the two simulators, one looking at the filtered light simulator and then looking at the black body simulator. So let's go ahead and take a look at the filtered light simulator first and as we open this up we will see a number of different things. We will see the simulator up here which will show the source that's being emitted and then its spectral distribution. This is the filtered transmission for the filters that you can place in the racks in between and this is what will be detected and then the detected color. Down here you will see the details about the light source and you can change the type of the light source from a black body to just a bell curve or to a straight flat curve or even looking for example at the sun. So you can change the different type of spectra of light source and you can change the filters. We have the U or ultraviolet filter, the blue filter, the visual filter, the red filter, atmospheric filter and you can also add your own filter and over here it shows you what wavelengths that that filter will allow to transmit through. So right now we're on the visual filter and the visual filter allows these wavelengths so things way off here in the red are not transmitted and way down here in the violet are not transmitted. So we can look at a quick example of how this works and for example if we wanted to take this visual filter and drag it up into the filter rack you can see how things have changed. Now that we are looking at this through the visual filter note how these two look very similar because that is the transmission. Those are the only wavelengths that can get through. So all of these other wavelengths over here and over here that were being emitted by the source are not being transmitted and this is a thing that is important because astronomers often want to study just those specific wavelengths emitted by various atoms and this filter then the filters then allow them to filter out all of those other areas. Now you can add multiple filters to this if you like so you could put for example ultraviolet filter in here and a red filter and what you'll notice now is that there is nothing getting through why is that? Well the red filter only lets through red light the ultraviolet filter only lets through ultraviolet light they don't have any overlap so the transmittance is nothing. So depending on the filters that you put up there you may get or may not get all of the light being transmitted. Now let's take a look at a little bit at the other lab that you look at and that will be the light and filters we're looking at the other simulator here and that is the black body simulator now you have a couple different things to look at here first of all it'll show the black body curve itself for whatever temperature you choose and that can be shown down here you have a couple of options to either highlight the area under the curve or indicate the peak wavelength for you and you can add multiple curves to this so for example if you wanted to look at a second curve and add another curve in that was at a much higher temperature you can now compare how it's a source at 9,000 degrees or so will compare to a 6,000 degree source what do we notice? Well let's indicate peak wavelength there and peak wavelength there notice how they are quite different and in fact you can look over here and see that the peak wavelength is much shorter for the higher temperature and that is a part of Veen's law that tells us that the higher the temperature of a black body the shorter the wavelength of its peak emission the other thing that we look at is the area under the curve that tells us the total amount of energy being emitted and that is given in the second column over here in this little box and we can see that the area under the curve is significantly higher for the green the green line then it is for the red line that means that regardless of where the temperatures are this green is giving off far more energy here all this energy more than the red is giving off this little bit down here so not only is it going to be giving off a shorter peak wavelength off towards the ultraviolet here but it is also going to be giving off far more energy and therefore be far brighter as well now the other thing that you'll look at on this and let's reset it and finish this up we look at the filter tab will show you four different filters that are often used in astronomy the ultraviolet filter the blue the visual in the red and we looked at these in the other simulator as well so it will tell you it'll show you here you know what is the transmission for each filter well ultraviolet allows in these wavelengths blue the visual filter and the red filter and you can then move this adjust the temperature for example to find out where things match up better and if you look here you know there we're reaching the peak of the red type filter out here so it peaks out much further and if we want to look with a peak of the blue filter is much further out so they're going to also look at different types of stars they're going to give us different way different energy transmissions based on the color of the star and we can then use what we call a color index often used is B minus V and that is essentially showing how much energy is being transmitted in the blue filter here and how much energy is being transmitted in the visual filter here and if you subtract those two magnitudes it will then tell you the temperature of the star so this B minus V color index which will change as we change the temperature so if we make that temperature much cooler watch how that B minus V gets larger and larger and larger and that is because we are now giving off very little cool to cool object is going to give off very little blue light relative to the visual light and therefore will look very very red in our examples if we go the other direction now that number gets very small because we are giving off lots of blue light and much less red light so it becomes negative as you have to recall that this is magnitudes and a large magnitude means a very faint object so the magnitude of the blue value would be smaller than the magnitude of the red value or the visual value so this would be a larger number a larger value meaning it is a it's going to be a smaller magnitude so smaller magnitude here means brighter and that is important to look at when we look at B minus V when that is negative that means that you had a smaller value and subtracting a bigger value and that can give you a negative and that means that's when you're getting to these objects that are very very hot and it all has to do with the way magnitudes are defined in terms of very small numbers meaning very bright objects so if we look at the numbers here just as an example at this object is you know is fainter in the red then it is in the visual then fainter in the visual then in the blue and fainter than the blue then it is in the ultraviolet just looking at what the magnitudes are remember that they're always backwards so that finishes up looking at the three simulations that you can be looking at for this lab we'll be back again next time to look at another one of these simulations so until then have a great day everyone and I will see you in class