 Greetings and welcome to the introduction to astronomy. In this video we are going to look at the variable star photometry lab and a couple of the simulators that are used there. And as you work your way through the lab don't forget to continue and look at the background information as well as that does include some important information to get you started and will keep you from getting lost when you jump right in to the simulators. So the first thing is several simulators to look at in this lab and let's look at each of them in turn and the first is the registration simulator and when we open that up you will see that we have a couple of different areas here. We have your work area that you're going to look at and the star field controls. There are three different star fields and the whole idea of these is then to line them up is to get them lined up together and you can do that right now you're only seeing one star field but you can align the second one by checking that off and then you'll see that there's two star fields and they have similar they have the same star so they're taken of the same region and in fact you can see some of the patterns down here the bottom here and the bottom here is being the same and what you want to do is line them up now of course it's hard to see there and you can use some of the options here like making the top field transparent so that you can actually see through and line up the stars so that they match up very closely with what we see. You can also find that inverting colors may help so that if you see them this way with a dark star and a light background you may be able to better line them up and eventually you're going to try to line up all three and make those adjustments to make them look so that the stars are all lined up as close as you can possibly get. Now you'll need this to be able to get those numbers to work your way through the rest of the lab. Now the next simulator we want to look at is the blink comparator simulator and this allows you to then line up the ones that you've already set up and in fact there are all of these observations in this table going down through a whole area here for epoch 1 through epoch 21 and what you can do is add some of them to your blink comparator so you could add this one for example and you could add another one and then you could add another here and let's see let's go down and add a couple just scattered around and what you're going to be looking for is for some changes when you actually blink these and you click on blink is you are looking for stars that are actually changing in brightness and you're going to eventually try to identify some variable stars. It's going to have you find a certain number of variable stars here and as you look at it you may notice certain stars are changing in brightness. Now if you notice as you notice those you will also if you're not seeing all of them you can also change go back and change the epochs that you're using so you could remove move some of them and put ones that are closer together or further apart or using different separations to really be able to find those variable stars and you're going to look for a total of five variable stars there and then once we've done that there's still more to this so that'll help you find the variable stars then you want to use the photometry simulator so the photometry simulator will allow you to imagine capturing the brightnesses of the stars and there are two different apertures that are used and the first one you can line that up on a star so you select it and get the star perfectly centered there and once you have that then you can center the other star on another star and it's going to have you look for the stars that you've already been using and you can then look at this and it will give you the information it will tell you the information about the inner disk where the star is and your comparison the outer ring here is meant to be black space so that you can get a comparison how much is being detected from something where there is not a star and you'll be able to subtract that out to get the true brightness of the star at the center here and that will give you the total number of counts and you can actually move the mouse over each of these and it will give you a count by number of pixels here so by what each pixel and how many counts were received in that now you can also use the magnitude difference you don't have to do the calculation yourself but it will actually calculate a magnitude difference between those two stars for you and you're going to need that information for certain areas to look at what the magnitude difference was here it does it with the counts just the number of counts here and then you can turn those counts into a magnitude now the last thing we want to look at is the last simulator here and when we go back let's clear this off and we'll go back and look at our final simulator which is the variable star photometry analyzer so now we want to be able to identify these variable stars that we looked at so if we take a look at stars you can select a comparison star and then your star of interest you'll want to look for stars that are for comparison stars you do not want to select one of your variable stars for example and then you can look to see if there are any magnitude differences over time so in this case of these two stars there does not seem to be a very big magnitude difference and as you look around and select other stars you will see other cases where there is a very significant magnitude difference and you can then use the difference tool to determine that magnitude difference by going from the top in the bottom here and estimating roughly where those are to find the magnitude difference for that and you can also look for the period when you look for the period you look for the longest line here so you'd zoom in to that so you'd select something very close to that and then zoom in around it to actually get it very close and what you'd find there is you'd get the period and if you look at this by phase instead of by time we can put that all together and you'll even see that as you get it way off from the period everything is just spread out but as you get closer and closer to that period everything seems to line up so you can actually see the light curve of the star that you're looking at of your star of interest so you can see how it varied in brightness you can determine the period is given to you here and you can determine the magnitude difference in these cases and you're going to look for that information and you'll use that and information from earlier on to identify even the type of variable star we have our lyrae stars we have sephiod stars and we have eclipsing binary stars all different types of variable stars that you can identify and what you're going to do is those five stars that you identified as variable in this field earlier on you're going to use those find the magnitude difference find the period and then use the light curve and that information to determine what type of variable star they are so that concludes this video on looking at the variable star photometry lab and the different modules that you'll use for that 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