No instrument
How to find north without a compass
Short answer
Put a stick upright in the ground, mark the tip of its shadow, wait fifteen minutes and mark it again. The line from the first mark to the second points roughly east.
Every method here depends on something outside you moving predictably: the sun across the sky, or the sky itself around the pole. None of them needs a magnetometer, which means none of them can be thrown off by a steel desk or a magnetic case.
They are also all slower and less precise than a compass, and the folk methods you may have heard, moss on the north side of trees and the like, are not on this list because they do not work.
Method
Step by step
In this order. Each step assumes the one before it is done.
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01
The shadow stick
Stand a straight stick upright on level open ground and mark the very tip of its shadow with a pebble. Wait fifteen or twenty minutes and mark the new tip. Draw a line between the two marks: it runs roughly west to east, with the second mark to the east, because the shadow tracks opposite to the sun. Stand with your left foot on the first mark and your right on the second and you are facing approximately north in the northern hemisphere.
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02
The sun at local noon
Local solar noon is when the sun is at its highest, which is not the same as twelve on the clock: correct for daylight saving and for how far you sit from the centre of your time zone. At that moment the sun is due south in the northern hemisphere and due north in the southern, and a vertical object's shadow points along the true north-south line. This gives true north, not magnetic, with no correction needed.
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03
The watch method
Hold an analogue watch flat. Northern hemisphere: aim the hour hand at the sun, and south is halfway between the hour hand and twelve. Southern hemisphere: aim twelve at the sun, and north is halfway between twelve and the hour hand. Undo daylight saving first. It is quick and it is worth about fifteen degrees.
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04
Polaris and the Southern Cross
At night in the northern hemisphere, Polaris is within a degree of true north and does not move. Find the Big Dipper, take the two stars forming the outer edge of its bowl, and extend that line about five times its own length. In the southern hemisphere there is no bright pole star: extend the long axis of the Southern Cross about four and a half times its length to reach the south celestial pole, and north is behind you.
How wrong can this be?
Accuracy
Polaris is the best of these at about one degree. The noon shadow is good to a few degrees if you judge noon well. The shadow stick and the watch method are both worth fifteen to twenty degrees, which is enough to walk out of a valley and not enough to hit a target.
Related
Other guides
The basic one
Which way is north?
If you are on a phone, press Start compass and turn until the bearing reads 000. If you are not, and the sun is up, stand with the sun on your right in the morning and you are facing roughly north.
Fixed installation
Aim a solar panel
In the northern hemisphere, face a fixed array due true south, 180 degrees. In the southern hemisphere, due true north, 000. Tilt it at roughly your latitude.
Line of sight
Aim a satellite dish
Look up the azimuth, elevation and skew for your postcode and your satellite, set the azimuth as a true bearing, then fine-tune on signal strength.