Declination is the angle between true north and magnetic north, used in geomagnetism and astronomy. The earth’s magnetic field is complex, and declination charts help with navigation. Electronic equipment can correct declination, and astronomers use it to fix elements on the celestial sphere.
In the study of geomagnetism, declination is the angle between true north and magnetic north, while astronomers use this term in the coordinate system they use to describe the fixed positions of stars in the celestial sphere. The intended meaning is usually clear from the context in which the term is used. Either way, it allows for very precise position measurements, a critical need when a small error can translate into a significant distance on the ground or in space.
The earth’s magnetic field is complex. It can vary from point to point, and over time, magnetic north and south tend to oscillate around the true north and south poles. Depending on where and when someone takes a compass bearing, the accuracy of the compass in terms of locating true north can be quite variable. In some parts of the world, for example, declination can go as high as 30 degrees. This means that when the compass points north, true north is actually 30 degrees away.
Declination charts are available for the surface of the Earth to help people navigate and use compasses accurately. If magnetic north is west of true north, this is expressed negatively, as -15°. When located in the east, the declination is positive. It can be written in two different ways, with a direction sign or a +/- symbol, as in 30E or +30. To correct for the variance, you need to add or subtract to get the correct fit.
Electronic direction finding equipment can automatically correct the declination and generate an accurate precise bearing. This is useful for sailors and hikers who rely on such equipment. It’s important to calibrate and test it periodically to make sure it’s working properly, as failures could be catastrophic. If not, you need to read a recent chart to determine how to correct the compass to get the correct bearing. Many compasses are adjustable to allow people to correct for declination before making a directional sighting.
Astronomers use declination to fix elements on the celestial sphere relative to the celestial equator. If something is north of the equator it has a positive reading, while items south are negative. The projected south pole, for example, is at -90° on the celestial sphere. This coordinate system allows astronomers to accurately observe and report stars and other phenomena. This acts much like latitude on Earth in determining where elements are located in relation to the imaginary line drawn at the equator.
Protect your devices with Threat Protection by NordVPN
