Objects & Inventions
Compass
A magnetic compass is a navigation instrument whose magnetized needle aligns with Earth's local magnetic field to indicate direction.
A magnetic compass is a navigation instrument containing a magnetized element that turns in response to Earth's magnetic field. One end points generally toward magnetic north, allowing users to determine direction when combined with a marked compass card or housing.
The compass does not normally point exactly toward the geographic North Pole. The angle between magnetic north and true north is called magnetic declination, and it varies by place and changes over time. Navigators account for that difference when precise direction is required.
Quick facts
- A magnetic compass aligns with the direction of Earth's local magnetic field.
- Magnetic north and geographic true north are not the same location.
- Magnetic declination is the angle between magnetic north and true north.
- Declination changes with location and slowly changes as Earth's magnetic field evolves.
- Magnetic compasses remain important for maritime navigation and as backups to electronic systems.
A surprising fact
A compass needle may need a small balancing weight because Earth's magnetic field tilts into or out of the ground rather than remaining perfectly horizontal.