Latitude and Longitude

[Music] when a ship is at sea there are no landmarks by which she can fix her position so latitude and longitude are used first let us see what is meant by latitude halfway between the North and South Poles a line can be drawn round the world dividing it into equal parts this is called the equator [Music] this point is the center of the earth [Music] all places not on the equator must be either north or south of it the distance of any place from the equator can be measured as an angle at the centre of the earth this angular distance from the equator is known as the positions latitude this angle remains the same no matter how large or how small a model globe may be latitude is measured in degrees or parts of a degree the equator is zero degrees the highest possible latitudes are 90 degrees north and 90 degrees south [Music] the latitude of this place is 45 degrees north while this one is 30 degrees south if a number of places are the same angular distance from the equator like these [Music] an imaginary line joining them can be drawn round the globe this is a line of latitude and all places on this line have the same north latitude in the same way a line of latitude can be drawn south of the Equator [Music] all lines of latitude are parallel to the equator and must cross the map or globe from west to east a ship whose position was given as 20 degrees south might be anywhere on this line therefore another measurement from a different direction is needed to fix its position so longitude is used any line which joins the poles and is drawn at right angles to the equator could be used [Music] as a standard most countries use the line which passes through the Royal Observatory at Greenwich this is called the Greenwich meridian [Music] anyplace not on this line must be either east of it or west of it the distance of any place from the Greenwich Meridian can be measured as an angle this is its longitude it is measured in degrees and parts of a degree the Greenwich line is zero degrees the greatest possible longitude is 180 degrees [Music] when a number of positions are the same distance west of the Greenwich Meridian an imaginary line can be drawn between the poles joining these points this is called a line of longitude or a meridian [Music] thus any line of longitude joins all places that are the same angular distance east or west of the Greenwich meridian all lines of longitude must meet at the poles and therefore must run from north to south across the globe or mat so if a ship's position is given as 20 degrees south latitude and 30 degrees west longitude by remembering that latitude is angular distance north [Music] or south of the Equator [Music] we can see that the ship might be at any of these positions which are all 20 degrees south and are all on the same parallel of latitude [Applause] [Music] thus the ship could be anywhere on this line [Music] longitude is the angular distance east or west of the Greenwich meridian so that a ship could be at any of these positions all of which are 30 degrees west so she must be somewhere on this line of longitude [Music] there is only one point which is both 20 degrees south and 30 degrees west where these two lines meet [Music] you