1. Terrestrial Coordinate System
NAVIGATION TRAINING
Section 2
Terrestrial Coordinate System

2. Table of Contents Section 1 Types of Navigation
Section 2 Terrestial Coordinates
Section 3 Charts
Section 4 Compass
Section 5 Nautical Publications
Section 6 Navigational Aids

3. Table of Contents Section 7 Buoyage Section 8 Position Lines and Fixes
Section 9 Tides
Section 10 Currents
Section 11 Weather

4. Terrestrial Coordinate System

5. Earth: A “not-so-perfect” Sphere
Shape and Size of the Earth - “a not-so-perfect sphere”
The Earth is an oblate spheroid (a close approximation to a sphere), but for navigational purposes, it is considered a “true” sphere with a circumference of 21,600 nm.
Equatorial diameter = 6,888 nm
Polar diameter = 6,865 nm (or 23 nm less)
If the earth were represented by a 12 in globe it would be depressed .04 inches or .10 centimeters.
Terrestrial Coordinate System
In order to make measurements on the sphere’s surface, we must develop a system of reference points.
When rotation is introduced, two reference points are defined- the points at which the spin axis pierces the surface of the sphere. On the Earth, these points are called the north and south poles.
For navigational purposes, it’s considered a “true” sphere with a circumference of 21,600 NM

6. Terrestrial Coordinate System
Great Circle: The intersection of a plane passing through two points on the surface of the earth and the center of the earth.
Great circle - A circle formed from the intersection of a plane passing through the center of the earth and thus dividing the earth into two equal parts.
This is the largest circle that can be drawn on the surface of the earth.
The shortest distance between two points on the earth is the arc of the great circle passing through them.
Equator - The great circle formed by a plane passing perpendicular to the polar axis. The equator divides the earth into northern and southern hemispheres and is of major importance because it is one of the two great circles from which all locations on the earth’s surface are referenced. N/S Hemisphere
Meridians (of longitude) - Any great circle formed by passing a plane through the center of the earth at right angles to the equator.
Prime Meridian - The second of two great circles that constitutes a reference line for the terrestrial coordinate system. This meridian passes through the original position of the Royal Greenwich Observatory near London, England. E/W Hemisphere

7. Terrestrial Coordinate System
Examples are: The Equator, Meridians of Longitude, the Prime Meridian being through Greenwich, near London, United Kingdom.
Great circle - A circle formed from the intersection of a plane passing through the center of the earth and thus dividing the earth into two equal parts.
This is the largest circle that can be drawn on the surface of the earth.
The shortest distance between two points on the earth is the arc of the great circle passing through them.
Equator - The great circle formed by a plane passing perpendicular to the polar axis. The equator divides the earth into northern and southern hemispheres and is of major importance because it is one of the two great circles from which all locations on the earth’s surface are referenced. N/S Hemisphere
Meridians (of longitude) - Any great circle formed by passing a plane through the center of the earth at right angles to the equator.
Prime Meridian - The second of two great circles that constitutes a reference line for the terrestrial coordinate system. This meridian passes through the original position of the Royal Greenwich Observatory near London, England. E/W Hemisphere

8. Equator
The great circle formed by passing a plane perpendicular to the earth’s axis halfway between its poles.
Great circle - A circle formed from the intersection of a plane passing through the center of the earth and thus dividing the earth into two equal parts.
This is the largest circle that can be drawn on the surface of the earth.
The shortest distance between two points on the earth is the arc of the great circle passing through them.
Equator - The great circle formed by a plane passing perpendicular to the polar axis. The equator divides the earth into northern and southern hemispheres and is of major importance because it is one of the two great circles from which all locations on the earth’s surface are referenced. N/S Hemisphere
Meridians (of longitude) - Any great circle formed by passing a plane through the center of the earth at right angles to the equator.
Prime Meridian - The second of two great circles that constitutes a reference line for the terrestrial coordinate system. This meridian passes through the original position of the Royal Greenwich Observatory near London, England. E/W Hemisphere

9. Equator
The equator divides the earth into northern and southern hemispheres.
One of the two great circles from which all locations on the earth’s surface are referenced.
Great circle - A circle formed from the intersection of a plane passing through the center of the earth and thus dividing the earth into two equal parts.
This is the largest circle that can be drawn on the surface of the earth.
The shortest distance between two points on the earth is the arc of the great circle passing through them.
Equator - The great circle formed by a plane passing perpendicular to the polar axis. The equator divides the earth into northern and southern hemispheres and is of major importance because it is one of the two great circles from which all locations on the earth’s surface are referenced. N/S Hemisphere
Meridians (of longitude) - Any great circle formed by passing a plane through the center of the earth at right angles to the equator.
Prime Meridian - The second of two great circles that constitutes a reference line for the terrestrial coordinate system. This meridian passes through the original position of the Royal Greenwich Observatory near London, England. E/W Hemisphere

10. Terrestrial Coordinate System
Small Circle: A circle formed from the intersection of a plane not passing through the center of the earth.
Examples are Parallels of Latitude
Small circle - A circle formed from the intersection of a plane not passing through the center of the earth.
Parallels (of latitude) - Any small circle on the earth’s surface that is perpendicular to the earth’s axis, parallel to the plane of the equator.
The equator is the only line of latitude that is not a small circle.

11. Measurement of Arc PRONOUNCED SYMBOL Degrees (°) Minutes (´)
Positions in relationship to Earth’s Coordinates system are expressed in:
PRONOUNCED SYMBOL
Degrees (°)
Minutes (´)
Seconds (´´)
Small circle - A circle formed from the intersection of a plane not passing through the center of the earth.
Parallels (of latitude) - Any small circle on the earth’s surface that is perpendicular to the earth’s axis, parallel to the plane of the equator.
The equator is the only line of latitude that is not a small circle.

12. Latitude
Latitude - angular distance north or south between the equator and the parallel of a point. Latitude is measured in degrees of arc from 0°-90° either north or south of the equator.
Latitude is measured along a meridian.
If a point lies between 0 and 90 degrees north of the equator, it is described as having northern latitude.
If a point lies between 0 and 90 degrees south of the equator, it is described as having southern longitude.
Latitude is abbreviated by the symbol “L” or f

13. Latitude Latitude is always expressed using 2 digits, e.g 49º
Always given first when giving a position
The length of 1 degree of latitude is always 60NM
If a point lies between 0 and 90 degrees north of the equator, it is described as having northern latitude.
If a point lies between 0 and 90 degrees south of the equator, it is described as having southern longitude.
Latitude is abbreviated by the symbol “L” or f

14. Parallels of Latitude

15. Prime Meridian
The meridian that passes through the original position of the Royal Greenwich Observatory near London, England.
Constitutes the second reference line for the terrestrial coordinate system.
Meridian - Any great circle formed by passing a plane through the center of the earth at right angles to the equator

16. Prime Meridian
All other meridians are referenced to the prime meridian; it divides the earth into the eastern and western hemispheres.
Meridian - Any great circle formed by passing a plane through the center of the earth at right angles to the equator

17. Longitude
Longitude - angular distance E/W between the prime meridian and the meridian of a point.
Longitude is measured in degrees of arc from 0 to 180 degrees east or west of the prime meridian.
Longitude is measured along parallels of latitude
If a point lies between 000 and 180 degrees west of the Greenwich meridian, it is described as having western longitude.
Longitude is abbreviated by the Greek letter lambda (l) or LO.

18. Longitude Longitude is always expressed using 3 digits, e.g 123º.
One degree of long does not equal 60 NM unless measured along the equator.
Always given after Latitude when giving a position.
If a point lies between 000 and 180 degrees west of the Greenwich meridian, it is described as having western longitude.
Longitude is abbreviated by the Greek letter lambda (l) or LO.

19. Lines of Longitude