Compass
A compass is a device that shows the cardinal directions used for navigation and geographic orientation. It commonly consists of a magnetized needle or other element, such as a compass card or compass rose, which can pivot to align itself with magnetic north. Other methods may be used, including gyroscopes, magnetometers, and GPS receivers.
Compasses often show angles in degrees: north corresponds to 0°, and the angles increase clockwise, so east is 90°, south is 180°, and west is 270°. These numbers allow the compass to show azimuths or bearings which are commonly stated in degrees. If local variation between magnetic north and true north is known, then direction of magnetic north also gives direction of true north.
Among the Four Great Inventions, the magnetic compass was first invented as a device for divination as early as the Chinese Han dynasty (since c. 206 BC), and later adopted for navigation by the Song dynasty Chinese during the 11th century. The first usage of a compass recorded in Western Europe and the Islamic world occurred around 1190.
The magnetic compass is the most familiar compass type. It functions as a pointer to "magnetic north", the local magnetic meridian, because the magnetized needle at its heart aligns itself with the horizontal component of the Earth's magnetic field. The magnetic field exerts a torque on the needle, pulling the North end or pole of the needle approximately toward the Earth's North magnetic pole, and pulling the other toward the Earth's South magnetic pole. The needle is mounted on a low-friction pivot point, in better compasses a jewel bearing, so it can turn easily. When the compass is held level, the needle turns until, after a few seconds to allow oscillations to die out, it settles into its equilibrium orientation.
In navigation, directions on maps are usually expressed with reference to geographical or true north, the direction toward the Geographical North Pole, the rotation axis of the Earth. Depending on where the compass is located on the surface of the Earth the angle between true north and magnetic north, called magnetic declination can vary widely with geographic location. The local magnetic declination is given on most maps, to allow the map to be oriented with a compass parallel to true north. The locations of the Earth's magnetic poles slowly change with time, which is referred to as geomagnetic secular variation. The effect of this means a map with the latest declination information should be used. Some magnetic compasses include means to manually compensate for the magnetic declination, so that the compass shows true directions.
How to use a Compass
What You Need:
- A compass
- A map (preferably topographic if you’re hiking)
Step 1: Understand the Parts of the Compass
Most basic compasses include:
- Baseplate – Flat surface with rulers for measuring.
- Magnetic Needle – Red end points to magnetic north.
- Rotating Bezel (Compass Dial) – Shows degrees (0°–360°).
- Orienting Arrow and Lines – Helps line up the compass with map north.
- Direction of Travel Arrow – Points in the direction you want to go.
Step 2: Hold the Compass Correctly
- Hold the compass flat in your hand at waist level, so the needle can move freely.
- Make sure the direction-of-travel arrow points straight ahead of you.
Step 3: Use a Map (Optional but Helpful)
If you're using a map:
- Place the compass on the map with the edge along your intended route.
- Rotate the bezel so the orienting lines match up with the north-south lines on the map.
- Turn the map and compass together until the red needle lines up with the orienting arrow inside the bezel — “red in the shed.”
- Now the direction-of-travel arrow shows the direction to walk.
Step 4: Follow the Bearing
- With the needle lined up inside the orienting arrow, keep the compass steady and follow the direction of the travel arrow.
- Keep checking to ensure the needle stays aligned — this keeps you on course.
Tips:
- Avoid metal objects or electronics nearby, as they can affect the needle.
- Magnetic North ≠ True North — maps are based on true north, so consider declination if accuracy is important.
How to build a compass
How to Build a Compass (Homemade Version)
🧰 Materials Needed:
- A needle or small straight metal pin
- A magnet (a fridge magnet will work)
- A small bowl of water
- A piece of cork, foam, or a leaf (something that can float)
- Optional: Paper towel or tape (to hold the needle on the float)
Steps:
1. Magnetize the Needle
- Rub the magnet along the needle in one direction only (not back and forth).
- Do this about 20–30 times to magnetize it.
- This aligns the needle’s electrons and turns it into a temporary magnet.
Why this works: The magnetized needle will now align with the Earth’s magnetic field, pointing north-south.
2. Prepare the Float
- Cut a small circle from cork or use a leaf or foam.
- Lay the needle gently on top.
- If using paper towel or tape, attach the needle securely to the float (be careful not to cover it completely).
3. Float the Needle
- Fill a bowl with still water.
- Gently place the float with the needle in the center of the water.
4. Observe the Needle Align
- The needle should slowly turn and align itself along the north–south axis.
- The end of the needle that was rubbed with the magnet will point toward magnetic north.
Tips:
- Make sure the water is still and there are no metal objects or electronics nearby.
- If it doesn’t work, try rubbing the magnet on the needle longer or replacing the needle and trying again.
Sun methode
If you have an analog watch with you, there is another and somewhat more reliable method, at least if it's daytime and the Sun is visible above the horizon. Lay the watch flat, and rotate it until the hour hand is lined up with the Sun, along a straight line of sight. The hour hand will form an angle with the number 12 on the dial. Divide the angle in half, and you'll have a line bisecting the dial – the end between the hour and and 12:00 is pointing South, and the other end is pointing North. Before noon, you measure clockwise from the hour hand, and after noon, counterclockwise. Remember, if your watch is set to Daylight Saving Time, you'll need to adjust the method accordingly (you can either set the hour hand back one hour, or just use the 1:00 mark instead of the 12:00 mark).
The principle is the same if you're in the Southern Hemisphere, but slightly different. If you're south of the Equator, the Sun is in the northern part of the sky. You hold your watch horizontally, and align the 12:00 marker with the Sun. North, not South, will be at the halfway point between the hour hand and the 12:00 mark.
This method works in the Northern Hemisphere specifically, and the reason is that the Sun, in the Northern Hemisphere, follows an arc across the Southern part of the sky (traditionally, artists have favored studios with Northern exposure, in order to get more diffuse, less harsh indirect light than you'd get from a Southern exposure). If you're in the Northern Hemisphere and facing the Sun directly at noon, you are looking more or less directly South, and using the position of the hour hand gives you the necessary hourly offset from which to determine where the Sun would be if it were noon instead of (say) 3PM.