Directions, angles and the star compass

Stand still and turn all the way around. You have turned 360 degrees. Every way of describing direction is a way of splitting that circle into equal parts.

The compass rose

A compass rose shows directions around a circle. North is 0°. Turning clockwise, east is 90°, south is 180° and west is 270°. The halfway points sit exactly between: north-east is 45°, south-east is 135°, south-west is 225° and north-west is 315°.

True north and magnetic north

A magnetic compass needle points to magnetic north, which is not quite the same as the North Pole. In Aotearoa the difference is more than 20 degrees, so trampers adjust their compass to match their map. Over a 5 km walk, forgetting this could put you well over a kilometre off course.

The star compass

Long before magnetic compasses, Pacific navigators crossed thousands of kilometres of ocean by reading the stars, Sun, Moon, ocean swells and birds. The modern star compass, kāpehu whetū, was developed by Hawaiian navigator Nainoa Thompson, based on the compass of Micronesian master navigator Mau Piailug. Navigator Jack Thatcher adapted it for Aotearoa using te reo Māori.

The kāpehu whetū divides the horizon into 32 houses where stars rise and set. That makes each house 360° ÷ 32 = 11.25° wide, much finer than our eight-point rose. A navigator memorises the houses of hundreds of stars, so the rising and setting of a known star shows which way the waka is heading. The top and bottom stars of the Southern Cross line up to point south when it stands upright.

This is living knowledge that belongs to the navigators and communities who have revived it. We can learn about the mathematics of their compass with respect, and design our own compass rose for our own maps.