Finding True North

Introduction

True North is where the Earth's rotational axis is imagined to emerge in the Northern hemisphere. By contrast, the North which a compass points to is the Magnetic North and this is currently some 5⁰ different.

True North can be established with reference to either the Stars or the Sun. Ancient Egyptians used an instrument called a Merkhet to take sightings of certain stars which appear to rotate around the North Pole and today we may refer to Polaris as the North Star or the Pole Star (although at the time of the Ancient Egyptions, ‘Polaris’ would not have been in this position).

Activity

The Sun can be used to find True North quite simply by placing a vertical stake in the ground and noting which direction the longest shadow points to. More accurately, such a stake can be used to centre a number of concentric circles (or a sheet of paper with concentric circles drawn on it can be attached to a board and a large nail driven into the centre).

Careful note is then made of where the end of the shadow (or the head of the nail) crosses a particular circle both in the morning then again in the afternoon. A line joining the two points marked creates an East-West axis and its Perpendicular Bisector (or Bisector of the Angle created by the two shadows) provides the North-South axis.