Shape Of The Earth, True Magnetic Direction

Question 1

Earth shape

Answer 1

Not a sphere, fatter at equator.
Known as an elipsoid.
21,600nk/40,000km circumference.
Diameter @ equator 6888.1nm.
Diameter pole2pole 6865nm.
Nmx1.852=km

Question 2

Earth rotation and direction

Answer 2

Tilted off its axis at 23.5 degrees.
Earth rotates west to east, anti clockwise when viewed from above.
The ecliptic is the term for the apparent movement of the sun around the earth.

Question 3

Geoid

Answer 3

The shape of the earth which is based upon the surface of the oceans under the influence of gravity and rotation alone is called a Geoid.

Question 4

Navigation reference system

Answer 4

Modern navigation systems use reference systems based on the ellipsoid shape of the earth.
The aviation industry uses WGS84 as the accepted standard for chart reference.

Question 5

Cardinal and inter-cardinal points

Answer 5

Cardinal:
North, east, south, west

Inter cardinal:
North east, south east, south west, north west

Question 6

Measuring direction

Answer 6

Measured clockwise.

Question 7

True and magnetic direction

Answer 7

Variation west, magnetic is bigger
Variation east, magnetic is smaller

Question 8

Magnetic variation

Answer 8

Angular difference between true north and magnetic north.
Lines joining points of equal magnetic variation on the earth are called Isogonals.
Sometimes true and magnetic north may appear to be co- located when viewed from a given position. In such a case, the value of magnetic variation between them is zero. Lines joining points of zero variation on the earth are called Agonic lines.

Question 9

Magnetic deviation

Answer 9

Deviation is the angle subtended between compass north and magnetic
north.
Deviation is calibrated in a procedure called a compass swing.