NAVIGATION TRAINING Section 2 Terrestrial Coordinate System

NAVIGATION TRAINING

Section 2

Terrestrial Coordinate System

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

Table of Contents

• Section 7 Buoyage• Section 8 Position Lines and Fixes• Section 9 Tides• Section 10 Currents• Section 11 Weather

Terrestrial Coordinate System

For navigational purposes, it’s considered a “true” sphere with a circumference of 21,600 NM

Earth: A “not-so-perfect” Sphere

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.

Terrestrial Coordinate System• Examples are: The Equator, Meridians of Longitude,

the Prime Meridian being through Greenwich, near London, United Kingdom.

Equator• The great circle formed by passing a plane

perpendicular to the earth’s axis halfway between its poles.

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.

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

Measurement of Arc

Positions in relationship to Earth’s Coordinates system are expressed in: PRONOUNCED SYMBOL

Degrees (°)

Minutes (´)

Seconds (´´)

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 either north or south of the equator.

• Latitude is measured along a meridian.

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

Parallels of Latitude

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.

Prime Meridian• All other meridians are referenced to the prime meridian; it

divides the earth into the eastern and western hemispheres.

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

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.

Lines of Longitude