Review of Earth Geometry

1. Review of Earth Geometry • Any plane that passes through the centre of a sphere intersects the surface of the sphere to form circles known as great circles, for example the equator. • Great circles which pass through the North and South Poles consist of two semicircles called meridians or lines of longitude. • The line passing through Greenwich is the prime meridian (0° longitude). • Lines of latitude are circles on the surface of the Earth parallel to the equator; they are assigned a number depending on the number of degrees they are north or south of the equator. • To fix a position, state latitude then longitude.

2. Review of Earth Geometry

3. Review of Earth Geometry

4. Review of Earth Geometry

5. Review of Navigation • A nautical mile is the length of the arc of a great circle which subtends an angle of 1 minute (1′) at the centre of the Earth. • 1 nautical mile (n mile) = 1.852 Km • 1 degree = 60 minutes (1° = 60′) • 1 knot = 1 nautical mile/hour • 1 knot = 1.852 km/hour • Speed = Distance/Time

6. Review of Navigation Example: Convert 15.6 n.miles to km Convert 22.8km to n.miles

7. Review of Navigation Example: How long will it take a walker to cover a distance of 13.8km if she expects to average 4km/h?

8. Review of Navigation Example: A ship sails due north for 2 hours 16 minutes at a consistent speed of 10 knots. How far did it travel (in n.miles)?

9. Review of Navigation Example: Convert 12knots to km/h Convert 16km/h to knots