 Greetings and welcome to the Introduction to Astronomy. In this video, we are going to look at the Blackbody Spectrum Simulator provided by P-H-E-T Simulations. And we'll be using that for the lab in this lesson. Now, once you go to the website linked to in the class, you should see something that looks much like this. And then what you need to do is to click on the play button, and that will lead you into the simulation itself. So do make sure that you have Flash installed properly on that. And then this will be able to run and all you need to do is to click on this, and that will load the simulation that you will need for the lab that we're working on this week. Now, once you get there, you're going to see a number of different controls. First of all, what you'll see is the section itself with the graph. And this is what you're going to want to look at. You're going to see the axes of the graph showing the intensity versus the wavelength. And that is important. And the wavelength in this case is shown in micrometers, which represent 1000 nanometers. So when you see a three micrometers or microns here, that would be the equivalent of 3000 nanometers. And you're going to see a control for the temperature. You can adjust the temperature and then a thermometer showing you what the temperature is here. An option to click to show a ruler will come back that to that in a little bit. And then controls to be able to zoom in and zoom out on both of the axes so you can see what's going on there. And then within the graph, what you'll see is a rainbow stripe here that shows the wavelengths of visible light from violet on this side to the red on this side. And that means that over here we have the ultraviolet and on this side we have the infrared. So if we look at the default here, what is it showing? So we see then that it is showing the, we see the wavelengths there, but we also see the black body curve shown here. Now that is the black body curve that is associated with the specific temperature given. So for 4800 Kelvin, this red line is the black body curve that you would get. And we see that the peak is here in the visible portion of the spectrum. This would be the temperature of a star a little bit cooler than the sun. And as we might expect, it gives off light that you would see in the visible part portion of the spectrum. Most stars will give off this kind of light because we see them. That's the light that our eyes are actually sensitive to. Now if we clear this, we can also look at other temperatures. So if we want to change this temperature to something hotter or colder, we could make it a much higher temperature, much hotter than the sun, up to 9000, over 9000 Kelvin. Now it's hard to see where that peak is, so that's where the zoom buttons come in. So if we want to zoom a little bit in there, now we can see where the peak is. And the peak of this curve is actually in the ultraviolet part of the spectrum. So most of the light of a star of a temperature of 9000 Kelvin would be given off in ultraviolet light, which we cannot see. So most of the light here we do not see, but it would still look visible to us. We could see it because it is emitting some light here and some light here across the visible portion of the spectrum. It's emitting a lot of blue and violet light and a little bit of red light. So it's going to tend to look blue to us. So a very hot star is going to look a bluish-white color. Now we could also look at objects that are much cooler. And what we would see in that case, let's go down to a much cooler temperature. And now it begins to disappear again. So as we get down to something, let's just stop at around 3000 Kelvin. And now of course we cannot see it, so we need to adjust the scale again. So we want to zoom in so we can see where is the peak for something that is about 3000 Kelvin. And in this case we see that the peak is over here in the infrared portion of the spectrum. So a star that is much cooler than the sun about 3000 degrees would be giving off mostly infrared light. However it would be giving off other colors as well. We can see that it gives off some red and some blue light. In this case it's giving off a lot more red than it is blue, so this star is going to appear red to us. But most of its energy is being emitted in wavelengths that we cannot see. The vast majority of the energy being emitted by a star of that temperature would be given off in the infrared portion of the spectrum. Now the other thing that I mentioned that you may want to use here is to click on the button that says show ruler. It will bring up a ruler that you can then use and there is nothing to measure with it but you can use it if you want to figure out where the peak is. So you can see where this peak is and you can make an estimate that maybe it's right around about 1000 nanometers or one micron. But if you want to measure it more accurately you can use this as a straight edge, lining it up with the peak. And you'd find out that this is actually maybe a little bit less than that and you may want to give an estimate of say 950 or 960 nanometers for the peak. So it's not to measure anything, you're not going to be measuring anything with it. It's just a good straight edge to be able to make sure you're looking straight up and down because it's very difficult when you have the peak up here when you make it big enough to be able to see to be able to accurately determine what those wavelengths are. So you're going to use this for a number of different situations that the simulation will give you. You will go to much cooler temperatures than this. You will have to zoom in and zoom out on both axes. So you can actually zoom here if you want to be able to see better and further out what happens to the curve. And there will be some cases for example when you go down to the very low temperatures you may have to zoom out quite a bit there to be able to find where the peak is. So you'll be doing some adjustments to that as you go to much hotter or much cooler temperatures. So that concludes this video on using the black body simulator of the PHET simulations. We'll be back again next time to look at another one of these simulations for the labs. So until then have a great day everyone and I will see you in class.