Home Work #1- Latitude and Longitude Lecture
January 22, 2010 Student Lecture Sheet
Home Work #1- Latitude and Longitude Lecture
Latitude.
Lines of latitude are called parallels and mark a full circle on the surface of the earth. The zero degree latitude is the equator. These lines run east to west and divide the earth in northern and southern hemispheres. All points that run north of the equator will have north latitudes and all points that run south of the equator will have south latitudes.
Longitude
Imaginary lines that run vertically, north to south, from the North Pole to the South Pole.
They form half circles on the surface of the earth and divide the earth in northern and southern hemispheres. The Prime Meridian serves as the starting point for longitude measurement, so is indicated as 0 degrees longitude. The Prime Meridian passes directly over the British Royal Observatory in Greenwich, England because that is where the coordinate system was invented. All points that run east of the prime meridian will have east longitudes and all points that run west of the prime meridian will have west longitudes
Using these lines to find a place
To find a place you look for
· the lines of latitude first
o lines of latitude show how far north[up] and south[down] of the equator a specific location is
§ 0 N…….0 S
· The lines of longitude next
o lines of longitude show how far west[left] or east[right] of the Prime Meridian a specific location is. …….
§ 0 W or …….0 E
Now let us try
Find the following place
1. 150 N 190 E
· 150 N
· Move 350 up from the equator
· 190 E
· Remaining at 150 N ,move right 190 E
Possible answers Come to class for answers
Cardinal Points
POINTS OF THE COMPASS
Navigation is the process of moving from one place to another, safely and efficiently.
These first navigators stayed close to shore and navigated by sight of landmarks or land characteristics that they could see. They did not have charts but lists of directions, similar to today’s cruising guides. When they could no longer see land, the navigators were able to determine their (north/south direction) by observing the height of the sun during the day and the North Star at night.
At other times ravens were used. They claimed that if the bird circled the boat without purpose, land was not near, but if it took off in a certain direction, the boat followed, knowing the bird was headed toward land. Of course, this only worked if the navigator could get close to land.
When the weather obscured the sun or the North Star, they were unable to see land. In time the compass was invented. It was crude and consisted of an iron needle, lodestone, straw and water. The navigator would rub an iron needle against a lodestone1, stick it in a piece of straw and float it in a bowl of water. The needle would point in a northerly direction.
Much more valuable, at the time, was the invention of the lead line (c.13th Century), which was a tool for measuring the depth of water and the nature of the bottom. This line was weighted with lead and had graduated markings to determine sea depth. The lead was coated with wax to bring up samples of the bottom.2
Subsequently mariners began to realize that maps would be helpful and began keeping detailed records of their voyages. These early mapmakers created the first nautical charts called Portolan Charts (c. 13th Century). The charts, created on sheepskin or goatskin, were rare and very expensive, often kept secret so that competing mariners would not have access to this knowledge. In addition, the trade routes superseded geographical size of land. The charts did not have latitude or longitude lines but did have compass roses indicating bearings between major ports. They were, of course, not very accurate because the ability to measure distances at sea had not yet developed, nor was there an accurate method to portray the spherical surface of the earth on a flat piece of material.
Early map makers use to draw a small 16 pointed circle on a map, and place an "N" to point to North. These early map makers surmised that the winds blew in these directions
Since the 1100's, compass bearings have been split into 16 different directions:
North - North North East - North East - East North East - East
East - East South East - South East - South South East - South
South South West - South West - West South West - West
West North West - North West - North North West – North
Charts
A chart is a special-purpose map, generally designed for a form of navigation, such as air navigation. There is a difference between charts and maps. Maps show land areas, political subdivisions, and topography. A chart details water areas and has reference lines on it to allow the navigator to graphically plot information. A hydrographic chart provides information such as water depths and locations of navigational aids. An air navigation chart may show land, but it provides the air navigator with elevations as well as the locations of navigational aids.
Maps
A map is a graphic representation of selected features of the Earth's surface, drawn to scale. A map is a compact data base an information storage and retrieval system-that does not require machine action. Instead, the skilled map reader retrieves information from the map.
A 32 cardinal model
This was all the accuracy a Mariner's Compass had to offer then. By today's standards, it was not very accurate. As spherical mathematics improved, it became more customary to give bearings in units of "Degrees" from Geographic North. In the 1920's, it became an accepted practice to indicate direction, called HEADING or BEARING, by a single number (0 to 360) representing degrees of a circle as measured clockwise from True North.
The Azimuth System
The azimuth system measures direction by dividing a circle into 360 equal parts, called degrees, and subdividing each degree into minutes and seconds. We measure direction in degrees, minutes, and seconds clockwise from north in a horizontal plane. Some marine compasses show both the cardinal point and the azimuth figures on their cards
Global Positioning Systems (GPS)
The Global Positioning System is a network of satellites in orbit above the earth. A GPS unit is basically a radio receiver. The satellites transmit to the GPS unit which interpolates the signals into latitude and longitude which are displayed on the unit. Typically signals from three satellites are needed to identify a specific position and a fourth to interpolate altitude. GPS3 units are accurate to within a few hundred feet of your actual location. They can be used to very accurately determine your location and establish compass courses.