2:51 errs welcome back this is the last video for I guess this is introductory chapter so after this we will begin with chapter 1 up your textbook and this last video has one topic which is pretty I think that probably many of you have seen this before but just just in case not or to maybe give you some details we talked about latitude and longitude also which is the answer to the very basic question of how do we know where we are on Earth's surface or really any surface or any any area of space and the answer to that is by using a greater coordinate system so the one that we use on planet earth and in this course is the latitude and longitude latitude being a grid of east-west lines like the rungs on a ladder remember latitudes the rungs being the things you step on as you're climbing a ladder these West lines north-south lines are longitude they are some of them are long I think I think that's the that's the thing there but either way longitude north south latitude is east-west you'll notice how wonderfully color-coded those are to help you remember yeah you like how I did that and so you can see here lines of latitude going east-west and lines of longitude coming south you've seen pictures of the worlds and I have a question there it says what's wrong with this map and it's it's more of an aesthetic thing you saw this a lot in maps made in the US in the 80s for sure when I was growing up probably before then during the Cold War largely as a matter of fact at the end of this video I'll show you another map that looks like that but it's something about this map that really drives me nuts and do you can you think of what it is what's weird about this map something in the other it's just like why would you do that so my issue is that North America and South America are in the center of the map which is great because I love I love America I like being the center however it needlessly splits up this the Asian continent which is really dumb and so I have a feeling used to see this a lot in the Cold War because it's like oh we're the most important I like the maps where we're on one side of the other none of the continents are broken up you don't need to break up the continents it makes for a very awkward map so that's my issue with this particular map you actually see that version of the map a lot nowadays a little less so but it's still out there okay so latitude is the angular distance in degrees of Arc measured north or south of the Equator right so the equator is zero degrees craters the one in the middle and as you go north or south you have increasing latitude the Equator is zero degrees North Pole lies at 90 degrees north coincidentally that's not a coincidence at all the South Pole lies at 90 degrees south this traditionally latitude was determined from stars positioned above the poles and so what that tells you is that we've known about latitude or how to measure latitude for quite some time now so the angle between the horizon and Polaris or the North Star was used in the northern hemisphere so if here if you're what are you doing in your backyard or if you're out on the water you do it any way you are and then north or in the hemisphere you basically measure the distance between you and the North Pole let's do it I don't know what which one of these looks better and that is the the distance the latitude that you are at and it's the angle between the horizon and a constellation known as the Southern Cross in the southern hemisphere it's not called the Southern Cross with anything related to the United States or our sordid history it's because it's a constellation less in the southern was fear it's called the Southern Cross and that's how you would get latitude in the south and so as I mentioned the thing to know here is that latitude is relatively easy to measure and because of that people have known about latitude for or known how to measure latitude for quite some time right and so here are degrees of latitude these are the sometimes let me call parallels and they start at the equator at 0 degrees 15 30 45 60 you usually see that when divisions of 15 um however there there's all the numbers in between them as well they don't north and south of the equator longitude is the angular distance measured east or west of a starting line any starting line will do unlike the parallels all meridians are the same length so these are called parallels as you'll see as you get closer to the poles they actually get smaller right the longest line of latitude is the equator and they get progressively shorter the higher the degree of latitude you're at longitude on the flip side all of them are the same length because they all start and end in the same place right they all start in either the North or South Pole and end in either the North or South call it depends on which direction you want to travel along that line but therefore they're they're all the same length oops the zero degree line of longitude runs through the Royal Observatory in Greenwich England and is called the prime meridian or the Greenwich meridian I've actually never really seen it called the Greenwich meridian but the textbook tells me that it can be called that I've always seen the primary longitude can vary from 0 degrees at the Prime Meridian to a hundred eighty degrees east or west right unlike unlike latitude which only goes up to 90 degrees north I asked the question on test once where does this particular thing happen on the planet and somebody told me at latitudes greater than 90 degrees which I assume they must meant in Hatteras because if you go past 90 degrees you've gone past the North Pole and you must be floating somewhere in out of space needless to say they were wrong there are no lab to its greater than 90 degrees now the point halfway around the earth from the prime meridian is the International Dateline professor Sylvan yes student in the back of the class what's the deal why do the British get to have the Prime Meridian and everybody measures it from them that's a really good question the reason that they get to have the Prime Meridian so if this is the zero Degree one that would be granted English would be somewhere around here the reason that they get to do that is because they're the ones who found out how to measure which I'll tell you about so the earth turns through 360 degrees of longitude because we're spinning along that access they're spinning this way not that way this way although we're a little tilted right but the earth is spinning that way so I'm spin through 360 degrees of longitude every 24 hours which means 15 degrees every hour this gives us a time-based method for determining longitude which was developed at the end of the 18th century remember 18th means the 1700s it's always one less in terms of hundreds 18th century is in 1700s because the first century was a zero or whatever you call that it required measuring latitude required the development of an extremely accurate clock called a chronometer and longitude can be calculated by knowing the time at the prime meridian which is determined from the chronometer because it keeps track of time at the prime meridian at noon and your local position which is determined from the Sun right so basically it's the that when your son is at the highest whatever the difference between the time that it is where you are and the time that it is the prime meridian is your degrees of longitude this was this was originally figured out as the result of like the original XPrize basically back in the late 1700s it was deemed that it would be incredibly incredibly valuable for the British Navy for any Navy at the time but for the British Navy who at that point where the the dominating ones in the world to be able to determine longitude and so they had a contest where they gave away a lot of money to whoever could figure out how to measure longitude while you're at sea and that's actually the subject of a book that might actually just be called longitude but there's a book about it and I forget the guys name we talk about in textbook who figured this out and figured out the whole chronometer thing is really interesting story and essentially it was like the first XPrize where some large amount of money was offered to figure out some scientific question of interest so this happened to be one of military interests but that's that's how we originally figured out how to measure longitude and that is why the Prime Meridian goes through Greenwich England because they figure it out first so like I mentioned longitude as it's these are these lines and the difference between here and here it takes one hour right to get there if you if you know the time and the prime meridian how many hours is it going to take to get to 45 degrees or how many hours is it going to take for the earth to spend forty five degrees three hours right and so these these are lines of longitude you know what in hindsight at the end of that that particular sector now in hindsight I probably should have had the scientific method with this section because I think that maybe that would have been better more equal breakup but that's okay um so guess what guess watching 50 winners you've made it you've made it to the end of the first lecture this is probably exciting news to you because you are now one seventeenth of the way through the course 17 chapters more or less in the both 16 official chapters Plus this one introductory chapter you may have noticed that I am quite the dapper dresser I've had a different watch oh I'm not even wearing I supposed to have a different watch you know every every lecture in this first lecture series and then I blew it to 51 hours here it is I'm gonna put it on now watch number four of the series thus far now I'm not rich so this this watch thing can really only go on for so long before I rather have watches but I want to keep you entertained so I promise that I will try not to wear the same shirt twice