*Dimension of navigation* :

*Position*: a point defined by stated or implied by coordinates.*Direction*: the position of one point in space relative to another without reference to the distance between them.*Distance*: the spatial separation between two points and is measured by the length of a line joining them.*Time*: defined in many ways : the hour of the day and an elapsed interval.

**EARTH’S SIZE AND SHAPE :**

The earth is not a perfect sphere, the diameter of the equator is 6,887.91 NM while the polar diameter is approximately 6,864.57 NM. The difference in these diameter is 23.34 NM. The ratio between the difference and the equatorial diameter is 1 : 295. (23.34 : 6,887.91)

Since the equatorial diameter exceeds the polar diameter by only 1 part in 295, the earth is nearly spherical.

The **Equator** is a great circle around the earth’s middle, exactly half way between the North Pole and the South Pole. When looking at a map, latitude lines run horizontally. **Latitude lines are also known as parallels **since they are parallel and are an equal distant from each other. Degrees latitude are numbered from 0° to 90° north and south. Zero degrees is the equator, the imaginary line which divides our planet into the northern and southern hemispheres. 90° north is the North Pole and 90° south is the South Pole.

**LATITUDE AND LONGITUDE**

**LONGITUDE / MERIDIAN (GARIS BUJUR) : **

The latitude of a point can be shown as 45oN or 30oS of the equator, but there is no way of knowing whether one point is East or West of another. This difficulty is resolved by use of the other component of the coordinate system, **longitude**, which is the measurement of this east-west distance.

In the same way that the Equator separates the Northern and Southern hemispheres, the Greenwich Meridian divides the East from the West. The zero degrees longitude line runs from the North Pole to the South Pole, passing directly through the Old Royal Observatory building at Greenwich in South East London. It is the basis for timekeeping and navigation throughout the world.

The degrees continue 180° east and 180° west where they meet and form the International Date Line in the Pacific Ocean. Greenwich, the site of the British Royal Greenwich Observatory, was established as the site of the Prime Meridian by an international conference in 1884.

To precisely locate points on the earth’s surface, degrees longitude and latitude have been divided into minutes (‘) and seconds (“). There are 60 minutes in each degree. Each minute is divided into 60 seconds. Seconds can be further divided into tenths, hundredths, or even thousandths

**DISTANCE **

Distance as previously defined is measured by the length of a line joining two points. In navigation the most common unit for measuring distance is the nautical mile (NM). Reminding that the circumference of the earth on equator or Great Circle is 21600 NM.

**SPEED :**

Closely related to the concept of distance is speed, which determines the rate of change of position. Speed is usually expressed in miles per hour. If the measure of distance is nautical mile, it is customary to speak of speed in terms of knots. Thus, a speed of 200 knots and a speed of 200 nautical miles per hour are the same thing.

DIRECTION :

Direction is the position of one point in space relative to another without reference to the distance between them. The time-honored point system for specifying a direction as north, north-west, west, east, south etc is not adequate for modern navigation. It has been replaced for most purposes by a numerical system.

The numerical system divides the horizon into 360 degrees starting with north as 000 degrees, and continuing clockwise through east 090 degrees, south 180 degrees, west 270 degrees and back to the north. The circle is called a compass rose, represent the horizon into 360 degrees.

Since determination of direction is one of the most important parts of the navigator’s work, the various terms involved should be clearly understood. Generally, in navigation unless otherwise stated, all directions are called true (T) directions.

**COURSE** is the intended horizontal direction of travel.

**HEADING** is the horizontal direction in which an acft is pointed.

**TRACK** is the actual horizontal direction made by the acft over the earth.

**BEARING** is the horizontal direction of one terrestrial point from another.