 Greetings and welcome to the Introduction to Astronomy. In this video, we are going to look at a lab showing how the Hertzsprung-Russell diagram works, and that is a, the Hertzsprung-Russell diagram itself is a plot of a star's temperature versus its luminosity. And we find that there are patterns that occur, including things like the main sequence, giant stars, and supergiant stars, and white dwarf stars, so that the stars tend to group into various areas. And we're going to try to look at that when you use this simulation. Of course, make sure you look at the background material first because some of the answers for the earlier questions you will find work in there. And if you jump right to the simulator, you're going to miss out on that. So let's go ahead and take a look at the simulator, which is what I want to do here. And when we open the simulator, what we'll find is that there are a number of different boxes. Here we're looking at sizes of stars compared to the sun, so the star will be here, and our sun will be here for reference. So you can change the properties as to what is located at the cursor mark. So you can change the temperature of the star. Right now, it's set for about 5,800 Kelvin, the temperature of the sun, and for one solar luminosity. And then it will do the calculation for you here using this equation to determine what the radius of that star will be. In this case, it will be one solar radius because our star is the same as the sun, but we'll be able to change that as well. And you can look at various other options here. You can change whether you want to show the main sequence. Let's look at a couple of these options here. You can change if you want to show the luminosity classes, the different types of stars, the giants and the super giants. You can show what is called the instability strip where stars are not stable, and we get lots of variable stars there. You can also look at some of the stars that you're plotting. You can plot just the nearest stars. Let's turn off a couple of these just to make it a little easier. So these are the nearest stars to the sun, or you can plot the brightest stars, which are these. So you can see that there's quite a difference between those. And you can also plot them both together to really see the differences. And if you look for the overlap, you'll see that there isn't very much between them, just a few stars. So you will have to look at those and it'll give you some understanding of the different types of stars that we see. Now looking at the other controls here, as you change the temperature, and let's go ahead and turn this off. But as we change, for example, the temperature, if we make a star hotter, and we leave the luminosity the same, remember we're changing only one thing at a time. So we're changing the temperature, which means we move to the left. So this star is no longer a star that is on the main sequence. It is actually often below the main sequence. So you could change the temperature to a much hotter star, but you could also that would also change the luminosity. So if you want to find where that would be on the main sequence, you can bring it back up to the main sequence and find that that star would be about twice the size of the sun, 52 times the luminosity, and about twice the temperature. So the calculation will be done for you. You don't have to go through using this to calculate. You can get the radius right here. It'll give you that number. Now you can also, if you like, take the cursor and drag it around. So if you want to look at other regions, if you want to see what stars are like down here on the main sequence, you don't have to try changing things. You can say these very stars on the very far lower right of the main sequence, well, those are very small stars, about a tenth the diameter of the sun, and very, very small in terms of luminosity. If we put our luminosity classes back on, you can then drag that cursor and what is a giant star like? Well, 40 or 50 times the size of the sun, and a super giant star, as you go up into the upper corner here, can be thousands of times the diameter of the sun. So temperature gets very cool, but luminosity gets tremendous because these stars are very, very large. So you can play around with that, and it will ask you a number of questions about the different types of stars that you see at various locations on the main sequence and at various locations on the HR diagram itself. So you can go ahead, so you'll get to go ahead and change a number of those things, but that's a little bit about how the controls work on this simulation. So that concludes this video on using the Hertzsprung Russell diagram simulator. We'll be back again next time to look at another one of these demos. So until then, have a great day everyone, and I will see you in class.