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Finding true north

You will need:

  • One 30cm stick with a fine tip on one end
  • Two small rocks
  • String


1. Place a straight stick straight upright in the ground so that you can see its shadow.

The taller the object is, the easier it will be to see the movement of its shadow.
The narrower the tip of the object is, the more accurate the reading will be.

Make sure the shadow is cast on a level, brush-free spot.

2. Take your first reading in the morning, at least an hour before midday. Mark the tip of the shadow with a small object, such as a pebble, or a distinct scratch in the ground.

Try to make the mark as small as possible so as to pinpoint the shadow's tip.
3. Use a length of string exactly the same length as the first shadow you record.
Keep checking shadow's length every 10-20 minutes. You will find that the shadow will continue to shrink as the time approaches midday, when shadows are at their shortest.

4. The shadow will begin to lengthen after midday. When the shadow grows to exactly the same length as your string from the first measurement, mark the spot.

5. Draw a straight line connecting the first and second marks as above. This is your east-west line.

6. If you stand with the first mark on your left and the second on your right, you will be facing in the approximate direction of true north.

7. For an exact reading, your two marks need to be made at exact intervals before and after noon where you are, which means when the sun is at its highest point in the sky. 

Why Does This Happen?

Magnetic north is different to true north.

Magnetic north is found by your compass, which is attracted to the magnetic field
surrounding the Earth itself. True north is the direction of the Earth's North Pole.

The difference between magnetic north and geographic north is called magnetic declination, with the difference varying between different places on the planet.

The shadow tip method works by knowing that the Sun travels across the sky from East to West everyday, and that at some point in time the Sun has to reach it's highest point of travel , i.e. midday. Midday time is different at every point on the Earth's surface, so finding true north requires you to take a measurement at the location in which you are standing.

Midday time on your watch will be different to midday time found by the shadow method.
Towns and cities have been placed in 'time zones' so that people in a 'time zone' all operate off the same time. If your town is in the middle of a time zone your shadow method would have found midday to be very similar. However if your town is on the edge of a time zone, your midday found by the shadow method may be quite different.
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