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Magnetic Field - Declination Component for the Epoch 1995.0 |
What this map layer shows:
The difference between the headings of true north and magnetic north, in increments of one degree.
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![opens the U.S. Geological Survey home page](https://webarchive.library.unt.edu/eot2008/20090115032737im_/http://nationalatlas.gov/images/LOGOS/MLD/logo_usgs.gif) |
Background Information |
Sample Map
Magnetism is a force produced between electric currents. Electric currents within the core of the Earth create a magnetic field which surrounds the Earth. This field is what causes a compass needle to point north, and it can be seen in the aurora that is sometimes visible at high latitudes. The magnetism of the Earth is referred to as geomagnetism.
For thousands of years, people have tried to solve the mysteries of the Earth's magnetic field, making the study of geomagnetism one of the oldest of the geophysical sciences. As early as the 1600s, scientists recognized the need for accurate and continuous measurements of the Earth's magnetic field. The first permanent magnetic observatories were established 150 years ago. Today, a global network of more than 200 magnetic observatories, supported by individual national agencies, provides the data that form the foundation for the modern science of geomagnetism. The U.S. Geological Survey (USGS) operates 13 magnetic observatories as part of this global network.
As our society becomes progressively dependent upon advanced technological systems, our need for geomagnetic data increases. Information collected on the Earth's magnetic field is used to meet the growing needs of Federal, State, and local governments, industry, academia, and the public. We use geomagnetic data for mineral exploration, military and commercial navigation, and geologic dating. Geomagnetic storms (rapid variations in the magnetic field) pose significant hazards to satellites, electrical power distribution systems, radio communications, and geophysical surveys. The collection of geomagnetic data allows scientists to provide advanced warning of geomagnetic storms. An advanced warning of even a few minutes can save millions of dollars in losses by permitting satellite and power system operators to take mitigating actions.
Scientists at the USGS and at other agencies around the world compile data on the magnetic field in five year increments, which is then used to produce a model of the magnetic field called the International Geomagnetic Reference Field (IGRF). Each IGRF model is based on data collected in the recent past, preceding the model's construction, and is intended to represent the field in the near future, following the model's construction. Therefore the model for Epoch 1995.0 is designed to reflect the magnetic field from 1995 to 2000. When referring to a specific model, IGRF is followed by the epoch, as in IGRF 1995.
There are five basic elements that describe the direction and intensity of the forces within the magnetic field. Direction is described by declination and inclination; intensity is described by three components: horizontal, vertical, and total field intensity. Five additional elements describe the change, or secular variation, in the basic elements over time. Declination is an important measurement because the magnetic poles of the Earth do not line up precisely with the rotational axis of the Earth. This map layer was produced by the U.S. Geological Survey.
The Magnetic Field - Declination Component for the Epoch 1995.0 map layer
shows the declination component as isogonic lines (lines of constant declination of the Earth's magnetic field), derived from the International Geomagnetic Reference Field (IGRF) for the epoch 1995.0. Isogonic values are provided in one-degree increments and show the difference between the headings of true north and magnetic north. The declination component changes smoothly over most of the Earth except in a region surrounding each geomagnetic pole. Near the geomagnetic poles, the isogonic lines crowd closer and closer together. Also available in the National Atlas are nine additional map layers describing components of the magnetic field. More detailed information on geomagnetism is available from the USGS National Geomagnetism Program and from the National Geophysical Data Center Earth Magnetics page.
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![](https://webarchive.library.unt.edu/eot2008/20090115032737im_/http://nationalatlas.gov/images/common/transparent.gif) |
![](https://webarchive.library.unt.edu/eot2008/20090115032737im_/http://nationalatlas.gov/images/common/transparent.gif) |
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