Navigation Elements

• Know the four elements of navigation.

Overview Earth’s Size and

Shape Position Direction Distance Time

Pt A

Position

Pt BDirection

DistanceTime

Earth’s Size and ShapeFor most navigational purposes,

the Earth is assumed to be a perfect sphere.

Measured at the equator, the Earth is approximately 7,926.41 miles in diameter, and the diameter through the poles is approximately 7,901 miles.

Earth’s Size and ShapeGreat Circles and Small Circles• Defined as a circle on the surface of a

sphere whose center and radius are those of the sphere itself. It is the largest circle that can be drawn on the sphere.

• The single most important aspect of great circles for navigators is that the arc, or piece of the circle, is the shortest distance between two points on a sphere.

PositionLines of reference are

necessary in order to locate specific points on the Earth.

• These lines are known as parallels of latitude and meridians of longitude.

• The numbers representing a position in terms of latitude and longitude are known as coordinates of that position.

North Penn N40-14.05, W075-18.58

PositionLatitudeParallel with the equator are lines

of latitude. Each of these parallel lines is a small circle, and they have a definitive location.

The equator is latitude 0o, and the poles are located at 90o latitude. Letter designators N and S are used to show which latitude is meant.

Longitude The Greenwich Meridian is

sometimes called the prime meridian, although it is actually the zero meridian

Longitude is counted east and west from this meridian through 180o

DirectionDirection is the position

of one point in space, relative to another, without reference to the distance between them.

The points of a compass are not adequate for modern navigation. It has been replaced, for the most part, by a numerical system.

DirectionSince determination of

direction is one of the most important parts of the navigator’s work, the various terms involved should be clearly understood.

• Course• Heading• Track

Direction

DirectionA line that makes the same

angle with each meridian is called a rhumb line.

• Flying this sort of path results in a greater distance traveled, but it is easier to steer.

• Between two points on the Earth, the great circle is shorter than the rhumb line, but the difference is negligible for short distances (except in high latitudes).

Rhumb Line Great Circle Line

Direction

DistanceMeasured by the length of a line

joining two points. In navigation, the most common unit of measuring distance is the nautical mile.

• The nautical mile is about 6,076 feet.

• Statute mile is 5,280 feet• Speed: If the measure of distance

is nautical miles, it is customary to speak in terms of knots.

TimeThe Earth makes a complete rotation of 360o during a 24 hour day.Greenwich Mean Time

• Greenwich Mean Time (GMT) is the time of day at any given moment at Greenwich, England.

• Zulu Time Time zones are derived as +/- from Zulu Time

Phonetic Alphabet and Morse Code

Navigation Elements

• Know the four elements of navigation.