# 9.4.3 Shortest Distance between Two Points

9.4.3 Shortest Distance between Two Points

1. The shortest distance between two points on the surface of the earth is the distance measured along a great circle.

 Shortest distance between points D and M    = ( θ x 60 ) nautical miles

Example:
In the above diagram, calculate
(a) The distance from P to Q, measured along the parallel of latitude 48o S,
(b) The distance from P to Q, measured along the route PSQ, where S is the South Pole.
State the shorter distance.

Solution:

(a)
Distance from P to Q, measured along the parallel of latitude 48o S
= 180 x 60 x cos 48o ← (angle PMQ = 180o)
= 7266.61 n.m.

(b)
Distance from P to Q, measured along the route PSQ, where S is the South Pole
= 84 x 60 ← (angle POQ = 180o – 48o – 48o = 84o)
= 5040 n.m.

The distance from P to Q, measured along the route PSQ in (b), where S is the South Pole, is shorter than the distance measured along the parallel of latitude in (a).

 The shortest distance in the above example is              the distance along the arc of a great circle,      which passes through the South (or North) Pole.