North?

Last Weekend I went Rogaining, that is long distance cross country orienteering.

It involves navigation using a map and compass, one factor in navigating using bearings on a compass calculated from a map is adjusting for declination. Declination is the difference between true north (the direction of the geographic north pole) and magnetic north (the north a compass points to).

After talking to a friend prior to the Rogain event and discussing the idea of declination and  ‘north’ I did some research and found some interesting stuff.

Firstly, declination varies across the world in a strange way, almost like contour lines eminating from the poles. Declination also changes over time (see the great animation below), due to the magnetic poles moving and to flows of magnetic metals beneath the earths crust .

Secondly, we wondered how was the north pole discovered if a compass does not point to the geographic pole? Well, you can use stars, or the sun. If using the sun, around noon you follow the diagram below, and also see below for the astral version.

But then, how was north calculated prior to accurate time pieces? AND, how did someone discover that those rules actually work without accurate maps?!

Change in declination over last 300 years

Calculating true north using the midday sun.

Calculating true north using the stars.