 Greetings and welcome to the Introduction to Astronomy. In this week's Misconception in Astronomy we are going to talk about Polaris and find out is it the brightest star in the sky? So what do we know about Polaris? Well Polaris is not the brightest star in the sky. Let's start off by saying that it is also what is known as the North Star. So it is at or very close to the North Celestial Pole. Now if it's not the brightest star in the sky, it is the brightest star within its constellation. It is in the constellation of Ursa Minor and the star is Alpha of Ursa Minoris. Alpha means signifying generally the brightest star within that constellation. So the brightest star would be the Alpha star and Beta and Gamma and so on through the alphabet. Now what we know about Polaris we can look up its absolute magnitude and find that it has an absolute magnitude of about plus two. Now that makes Polaris not a very bright star. In fact it comes out right around 50th brightest star in the sky. So in even excluding our sun there are still nearly 50 stars that are brighter than Polaris. So why in this case then if it's only about the 50th brightest star why is Polaris so important? Well it's important because of its location in the sky. It is very close to the North Celestial Pole. Now we see here Polaris on the sky chart and you can see Polaris here and down here just a little bit below it is the North Celestial Pole where all of those lines converge together. Now that's what makes this very important because identifying the North Celestial Pole had been important in the past for navigation at sea. Now when you're traveling on land you have a lot of landmarks that you can use and follow to keep you going in the right direction. However when you're out on the ocean far away from land the ocean looks pretty much the same in all directions and you may end up wandering especially wandering north or south and it's very difficult to tell. However it turns out that the altitude of the North Celestial Pole is equal to the latitude of the observer. So if you could observe Polaris and watch its position in the sky that would allow you to navigate and keep yourself on from drifting too far north or too far south. If you found yourself drifting north you would see Polaris getting higher and higher in the sky. If you drifted too far south it would get lower and lower in the sky and you can use that then to adjust your navigation. Of course on cloudy nights that would not help you but it would be a way to help keep you going in the same direction in a long trans-oceanic voyage. Now here we can see a little bit as to how that works. Here is something a little further south. Here is Polaris and you can see the star there very close to the pole. Now the pole itself would be somewhere right in the center of all these circles so Polaris is not quite there but all of the stars do make circles around the pole and you can watch and the one that stays still is Polaris. Polaris holds pretty much the same altitude and that would be how high is it above your horizon? That would then tell you this angle would tell you your latitude so what is your current latitude? You just have to measure how high Polaris is up above the horizon. Now of course on land the horizon can be blocked by trees and buildings and such however when you are on the ocean you have a nice clear view of the horizon and can get a nice measurement of this and again that helps you keep your latitude relatively steady as traveling across the oceans. So let's go ahead and finish up with the summary and we found out that Polaris is definitely not the brightest star in the sky. There are many stars that are brighter than Polaris. It's about number 50 on the list and it is important still because of its location in the sky which happens to be near the North Celestial Pole which has been helpful for navigation in the past. So that concludes this lecture on Polaris being the brightest star in the sky. We'll be back again next week for another Misconception in Astronomy. So until then have a great day everyone and I will see you in class.