Exercise Solutions to Chapter 11
Explain how sailors on a ship traveling parallel to a coastline at a known speed can
use parallax angle measurements to determine the distance to the shore.
The navigator measures the compass direction a1 to a prominent object
on the shore. For simplicity, assume he picks an object is near his beam
(side). Then, after several minutes he takes another measurement of its
direction a2. Knowing the time between observations and the ship’s speed
and course, he calculates the distance d the ship has traveled. This is
the baseline and the difference between the two angles (a2 a1) is the
parallax p. The small angle equation gives the distance D to the object.
d a 2