THE FORM OF THE EARTH

Who could say what the Earth’s like?

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SHAPE

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SHAPE•ICAO STANDARD – WGS84 (World Geodetic

System 1984)•2 Different Radius

•COMPRESSION RATIO : 1/297 (a-b/a)

POLAR RADIUS: 3432nm

EQUATORIAL RADIUS: 3443nm

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EAST & WEST

•EAST: Direction in which the Earth rotates. Anticlockwise to a person looking down on the N.Pole•WEST: Opposite to East

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EQUATOR

DEFINITION: Circle drawn on the surface of the Earth that divides the world into 2 equal

hemispheres. Its center is the same that the one from the Earth it self. (Great Circle & Rhumb line)

Sets a reference for North and South latitudes

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EQUATOR

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PARALLELS OF LATITUDE

DEFINITION: Circles drawn on the surface of the Earth parallel to the Equator that extend up to the Poles. Named by the angle between the plane of the Equator and the line joining the center of the Earth and any point on parallel (Small circles)

Extention: From 0º (Equator) to 090º N/S (North/South Poles)

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PARALLELS OF LATITUDE

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MERIDIANS OF LONGITUDE

DEFINITION: Semi circles drawn on the surface of the earth that joint the 2 Poles and

cross the Equator and all the parallels at right angles.

• The special one: PRIME MERIDIAN (Sets reference for East and West)

• Each meridian has an ANTI-MERIDIAN• Forms a complete GC with its anti-meridian

PROPERTIES:

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MERIDIANS OF LONGITUDE

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MERIDIANS OF LONGITUDE

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GREAT CIRCLEDEFINITION: Circle drawn on the surface of a

sphere with its center on the center of the sphere. E.g.: Equator and Meridians

PROPERTIES

• Connects any 2 points on Earths surface• Only 1 GC over 2 points (Exceptions)• Is the path RADIO SIGNALS follow ORTHOMORPHIC PATH• Short path: Shortest possible

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GREAT CIRCLEVERTEX OF A GREAT CIRCLE: Most northerly

and southerly points of a GC.

PROPERTIES

• Northern and southern are ANTIPODAL (Diametrically opposed)• 10,800 nm distant• At the vertex the direction of the GC is 090º – 270º• Are placed at 90º longitude from the point where

the GC cuts the Equator

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GREAT CIRCLE

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SMALL CIRCLE

DEFINITION: Circle drawn on the surface of a sphere that doesn’t have its center co-located with the

one of the sphere. E.g.: Parallels of latitude

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RHUMB LINEDEFINITION: Regularly curved line on the surface of the Earth that cuts all meridians at same angle. LOXODROMIC path.

PROPERTIES

• Only 1 RL through 2 points on Earths surface• Not GC (Exceptions: Meridians & Equator)• Mathematically will never reach the Pole (Spiral)• Distance with GC

Greater over long distances.

Increases with latitude

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RHUMB LINE

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RHUMB LINE

• Normally , flights of less than 1,000 nm are flown along a rhumb line.

• Long trips can be divided into short legs of rhumb lines.

• The easiest to follow because you only have to set a heading. Constant direction track

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RL & GC

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QUESTIONS TO THINK ABOUT

1. How can we know one vertex knowing the other?

2. How can we know the cutting angle between GC and Equator knowing one vertex position?

3. How can we know the vertex longitudes by knowing the long of the cutting point between Eq and GC?

4. How can we get one of the Earth’s radius knowing the other and the compression ratio?