 Greetings and welcome to the Introduction to Astronomy. In this video we are going to look at the motions of the sun lab, and this uses a couple of different simulators and some information to look at the motions of the sun, how the sun moves over the course of a day and over the course of a year. So as you look at it there are sections on seasonal motion that you can look at, which has one simulator, the sidereal and solar time simulator, and the daily motion with seasonal effects, which has the paths of the sun simulator that you'll want to look at. So we can look at both of these briefly. The sidereal and solar time simulator will open up and give you something like this, and it will show at a given time what the solar time is. This is our regular clock time, what we use, and it will give the astronomical time, the sidereal time, based on the star's positions. And at this point at the time of the vernal equinox you can see that it is 12 p.m. or 12 noon by solar time, meaning that the sun is directly on the meridian. The sidereal time, so for the star it goes by the right ascension of the star that would be on the meridian, so the sun would be on the meridian, and a star would be in the same direction would be at zero hours. So while that is our noon local time, astronomical time, that would be zero. So that would be the beginning of a new astronomical day. And you can then jump this forward a little bit at a time by changing, for example, advanced by one solar day, and if you click on that it will zip one day ahead. And what you find is one solar day later it is again noon by the regular earth clock, but it's a little bit past that by the sidereal time. The sidereal day is a little bit shorter, so it takes a little bit more time in the sidereal day to be able to run forward, and that's because the earth has moved a little ways along its orbit during this time, and that means it takes a little bit longer for it to rotate back into position to be pointing at the sun. So it takes a certain amount of time to point back to the vernal equinox, the zero hours here, distant stars, but it has to rotate a little bit more, taking that little bit of extra time, a few minutes, to get it back to the solar time. Now I just wanted to look at that one briefly. You don't need that one too much for this lab. I really wanted to primarily look at the other simulator that you will be using, which is the Paths of the Sun simulator. And that has a couple of different windows here, and you'll see the actual, the globe window here, time and location controls you can adjust, some general settings, which will be preset for you, some animation controls, and general information that you can look up that will kind of summarize everything for you. And what you can do here is look and reset things for various locations. So you could change, for example, the latitude if you wanted to see what things would be like at the equator, you'd put that to zero degrees, and then you can also drag the globe around to be able to see. And you can say, you know, what was the direction or the time when the sun was setting in the west on that day from that location. And you can bring it down until the sun's altitude reaches zero, and you can see the time of day that would have occurred over here. So there it shows you the time of day, and it will also tell you the altitude and azimuth, the position of the sun relative to that region, and the sun's right ascension and declination. So you can get all of that different information here, and you will need that in some of the cases. It'll ask you for the altitudes. It might ask you to record the times. And you can play through that to be able to see and to learn kind of how the seasons work and how long the sun is up in the sky. For example, if you take this much further north as a secondary example, let's go to close to the north pole. Let's go up to a latitude of 80 degrees. Now, at 80 degrees on the summer, what happens? Well, we can start animation here and let it run, and what happens to the sun? The sun never sets, so it will keep going around and around. And here in May at very close to the north pole, the sun remains above the horizon all the time. You can see that it never gets very high in the sky. It's following the yellow path here, but it will never get below the horizon. It never dips below the horizon as it would at lower latitudes. And you can actually bring that down even while it's running to look and see here at a lower latitude, the sun will rise and set. And if you went all the way down to the south, very close to the Antarctic at this time, then the sun would actually never rise. So you can actually look at that and look at the lengths of daylight and how they change. So those are some of the controls that you'll want to look at here. Again, you can adjust the day here, the month. You can also use the slider here to drag this back and forth. You can change the latitude of the observer, and you can run the animation and let it run through over and over. And you can also various things that you can check or uncheck to be able to see the information you need to be able to complete this lab. So that concludes this demo on using the motions of the sun simulator for the 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.