 Greetings and welcome to the Introduction to Astronomy. In this video we are going to look at the Cosmic Distance Ladder Simulator and the lab that we will be doing involving that. Now, there are a number of different sections of content here and there are four different simulators that you will be using looking at different ways of measuring distances. Don't forget to look at the other sections as well as those may be important for some of the work on your lab, so don't skip the sections just because they don't have a simulator. So let's go ahead and look first at these simulators and we'll start off with the parallax simulator. And as we open that up, what we'll see is a number of different windows as we do. In this case we see the lake on this side with the observer would actually see the person standing at the position of the X here and then various different presets that you're going to be asked to use. This adjusts the amount of error in the measurements and then you can take the measurements and finally there's a way to show a ruler for making additional measurements. So let's go ahead and take a look at doing an example here because what you're going to do with the first one is take some measurements and you can move the observer around as it directs you and what they will do is take a measurement. So we will see that with perfect measurements we know that the boat is somewhere along this line. We don't know the exact distance and parallax is measuring from two different positions. So if we move it to the other side and now take a measurement we have now triangulated the distance precisely. We know right where the boat is because we know it has to be along this line and it has to be along this line and those two intersect at only one point and we could then use that to determine the distances. Now you can also use in some cases here a ruler and the map scale to get this as well and it will ask you to do the ruler and you can take the ruler and drag it over there to measure that this is seven and a half map units away and we know that each map unit is 20 meters so that can actually tell you what the distance is. You can use that then to actually determine the distance and there are a couple of other presets and let me just look at one real quick here as we clear these. So let's clear our measurements. If we look at one of the other presets it's going to have some errors in the measurement. So you can see an example if we take a measurement here we now know that our object is somewhere in this shaded region. Well that doesn't help us a lot so let's take it from the other side and now we've narrowed it down so now we have narrowed down that our object is somewhere in this region. However that still gives us a little bit and we can find that if we take a third measurement you can even find it more accurately. So if you pick another section here take a measurement you have now narrowed it down a little bit more so the more measurements you can take the better you can isolate your object. So let's go ahead back and take a look at some of the other, one of the other ones that we're going to look at here and next we'll look at the spectroscopic parallax simulator. We can open that up and what we'll see is a number of different windows. This shows the intensity of the absorption lines which tells us really the spectral type or the temperature. So very cool stars over here, very hot stars over here. We can see what the spectrum might look like. You'll need this section here where it does the distance modulus calculation for you. So that's the distance that we're looking for in this case. And then you can adjust the apparent magnitude and the luminosity class of the object. Right now it is set for a star like the sun, a g2 star with a temperature much like our own sun. So that would then tell us for this star if that star has this apparent magnitude that number gets plugged in over here that's done automatically for you and then the distance is calculated automatically as well. So we can look a little bit about what you can what you'll be able to do here. Again you can adjust the magnitudes so you can change your magnitude of your object, you can change its luminosity class, you can take it as a luminosity class say five is a main sequence star, three as a giant star for example, and those are going to give you very different distances. If you notice the main sequence star has a distance of only three parsecs. The giant star has a distance of 34 parsecs and a super giant star is over a thousand parsecs away. And that's because a super giant star is really intrinsically very bright. It's way up here at a high luminosity so in order for it to appear this faint it has to be at a tremendous distance. Now the other thing that we can change is that we can move this along, we can move our spectral class along this way so we can look at cooler stars. Note that it's still as you can see the dot moving along the track for the super giant star since that's what we're in and that will change the distance as well as you go cross back and forth you can figure out the distances. So if you wanted to figure out that a b0 or sorry an 09 now super giant star with these properties and this apparent magnitude would be located at a distance of 362 parsecs. If it was fainter then it's going to be further away and if it was brighter then it would be much much closer to us. So that allows us to be able to determine the distances by looking at two things and we can look at in this case we look at the temperature and we look at the we look at the temperature and the luminosity if we can find its location on the HR diagram we can then use the distance modulus formula here to give us the distance. So let's look at our next simulator and what we have here is let's go back to our simulators and we were going to look at the cluster fitting explorer another way of getting distances and this is again fitting things to a main sequence but using an entire cluster of stars. So what you would find is we select our cluster here and let's look at in this case let's look at NGC 3293 and you'll see the stars and it plots the stars for them and we see that it doesn't match the main sequence very well at all but you can take this and drag it up and down to get your best fit to the main sequence. So where do you find it to be the best fit and maybe somewhere in here? So what you might have are stars evolving off the main sequence and some stars perhaps even evolving to the main sequence. So you can have a variety of different stars there but you try to get the best fit you can for the main sequence itself and once you do that then all you need to do is figure out the apparent magnitude and the absolute magnitude of one individual star to do this. Now the best way to do that is just to put a horizontal bar on and that will tell you that at this location the apparent magnitude we can read on the right of 13.2 and the absolute magnitude on the left is 3.5 and that will then give us the distance is calculated for us at 871 parsecs. So again you don't have to do the calculation you just have to put your two numbers in here using that horizontal bar. So that's all you do to determine the distances on this one and then we have one more simulator to look at briefly and that would be the supernova light curve fitting simulator. This is important because this is for very distant objects so each of these will work for different objects parallax works for very close objects supernovae can be seen across the universe so we can actually do this for much larger much more distant galaxies. So if we select a supernova and let's select 1999 AA there and you see there's a few points down in here and what we want to do is bring those up and try to match them to see how we can best fit the supernova. So this is the the red is the theoretical curve and the blue are the observations and now we use the same formula we did last time let's show our horizontal bar we have an absolute magnitude of negative 16 that's capital M so negative 16 goes there we have an apparent magnitude of 18.4 that goes here and that once we determine those two objects so once we've actually fitted properly that gives us a distance of 75.9 mega parsecs this is millions of parsecs away so you just have to fit everything as best you can and then put your two numbers in and the distance calculation will be done for you automatically so this is the way we can find the distances to some of the most distant objects in the universe so that concludes this video working with the various simulators of the cosmic distance ladder simulations. We'll be 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