this stage8 test. Hi there, this is Professor Jim Caffey again coming to you from Springfield, Missouri. And we are going to talk about chapter 18 on stars, a celestial census. So this will continue our examination of stars. We see a variety of stars in space. Some are blue, some are red, some are big, small, hot, cool, massive, mountain-massive. They come in all sizes and colors and temperatures. We do have a couple of stars that are the closest. They are about four and a quarter light years away. So when we take an image of them, we see them back in time for and a quarter of years. Takes that long for that light to reach us. And they are the closest minus the sun, which is eight light minutes away. So when you see the sun, that's how it looked eight minutes ago, not now. One of the things that I'm expert in is binary stars. So this is a visual binary, a cool a L dwarf binary. And we can see how it rotates in space with each other over time. It takes a long time. In a binary star system, you can have two stars of really any math to work with. High math stars are going to kill off the low math stars in a binary system. They evolve and they get absorbed into the bigger star. We can see the motions of stars in a binary system. We can look at the spectrum. In a spectrum, the dark absorption lines will shift back and forth as you see the two stars in the pattern. You only see that spectrum in pictures one and three where that motion is towards us or away from us. Remember, we recently talked about redshift going away and blueshift coming towards you. It's the stars or sideways. A tangential motion. We can't tell if they are moving away when you're us. And we call these measurements radio velocities. Now, in studying and accessing binary system, this is a special kind of bubble star or a binary star. And in accessing binary system, the one thing I'm the most expert at in my research is you have to you have to take images in camera pictures and measure light brightnesses as they go in front of each other just like a solar or a lunar eclipse. One light is going to be washed by the other and we can tell that by seeing less light at telescope. You can bind that with the radio velocities in the spectroscope and we get a full picture. I like this feature where I can zoom into me and talk to you for a minute. I like that. It makes me feel like I'm in a classroom. We have some failed stars. Brown dwarfs. We talked about these last time in the 70s. The brown dwarf is a star who could not kick on the normal nuclear fusion because it's mass is not great enough. It needs to be about 8% the mass of the sun. And the sun is actually a yellow dwarf star. So it doesn't take much star matter to make a star turn on and shine. We have a mass luminosity relationship with sunsarts. Seafians that pulsate, yellow big stars that pulsate and white dwarfs and stars. Now here is what I did for 20 years in my research with NASA in Missouri State University. This is where I said you can take an image of the two stars and collect all the light. So we can do that. And in that we get this neat light curve. It's what we call change in brightness over time and then it looks in binary system. We also use light curves in other areas of astronomy. But you can't see the two stars together in a telescope separate. They are too close to resolve as two. So we use this to get the spectra and we get the photometry, the light measurements. Unfortunately my telescope at Missouri State University did not have a spectra graph so we could not get radio velocity measurements. So I didn't get a full picture of what I wanted to. A part of eclipse in a closed-in binary system. What I can look like this depends on the size of the star. How fast they are moving. This one seems to be adding moderate clip. You see a smaller star. It is completely behind the other star for a period of time. We call it a total eclipse and then it starts coming out of eclipse and the light goes back to normal. These two men were giants in astronomy. Herds from Henry, Norris, Russell independently discovered the relationship between luminosity and surface temperature of stars for color, brightness, magnitude. This is summarized in the most important diagram that I can identify in astronomy. That is the HR Henry, Norris, Russell, Russell, Russell diagram. For a few stars, stars that are normal, they are burning hydrogen, they are not breathing weird. They fall on a curve called the main sequence. These are all normal stars, some are cool, some are big, some are hot. These are stars in their adult lives. We talk about stars as they are living in adult lives. Stars are proto-stars, babies, they are born, they can be gone, they are fusion, they shine for billions of years or however long, depends on their mass. The sun will burn for 10 billion years and has been for five. If we look at many stars, we see about 89% of all stars do fall on that main sequence. This chart looks different in many ways. You can graph this in many ways but you get the same result. This is a very powerful graph to get temperature measurements, brightness measurements, spectral class, surface temperature, how big is it? Is it a super giant? Is it a red giant? Is it a tiny red dwarf star? That is what I am an expert in. It is red dwarf in question binaries. Is it a dead star? It is a white dwarf. So we can look at the sun, a dwarf yellow star, and Vy canus adures a super giant. And when I say this is a super giant, I am really, it is really obnoxious. The sun is just this tiny tiny, you can't even see it, this dot. That is the sun put next to Vy canus adures. It is a, I think it is the biggest star that we know of. We have seen a dwarf companion star, a white dwarf around a very famous bright star called Sirius the Dark Star. That is going to complete the lecture for chapter 18 on the stars. Thanks for joining me and I hope you will continue to join my lectures. Well, as you enjoy that episode of 10 Minute Astronomy, and so check out all the other videos in that playlist for 10 Minute Astronomy and other videos on my channel and then hit the subscribe button right there. Thanks.