Equatorial radius > Polar radius
Equatorial circumference > polar by about 72 km
Avg radius 6400km
Avg circm 40000km
Earth rotates west to east
Parallels of Latitude – Parallel of latitudes are imaginary small circles on earth surface that are parallel to the equator. They are named N or S according to its hemisphere.
Geocentric Latitude- Latitude of a place is
Geographic Latitude – Is the angle between the plane of equator and Vertical at the
Geographic and geocentric latitude vary as the earth is not spherical . This variation is maximum at 45 degree North and 45 Degrees south and the Difference is 11.6′ .
1 Knot is a unit of speed equal to one Nautical mile per hour.
Geographical Mile – Is the angle of the arc of the equator subtending angle of 1′ at the center of earth . It is constant in length = 1855.3m .
Statute Mile or land mile is an arbitrary measure of length equal to 5280ft.
Cable – 1/10th pf a nautical mile.
True course – Is the angle at the ship between True north and ships head.
True Bearing – The true bearing of an object is the angle at the observer between True north indicated by the meridian and the line joining the observer and the object.
Compass Bearing – Angle at the Observer between compass north and the line of sight of object.
Relative Bearing – Angle at the Observer between Ships head and the line of sight of object.
Deviation – Is the angle between the magnetic meridian and North-South line of compass card.
Variation – Since Magnetic poles and Geographical poles are not in the same position, there is
The variation at a place is not constant .It changes because the magnetic poles of the earth is constantly changing.