Magnetic declination

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Magnetic declination

World Magnetic Declination 2020

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Magnetic Declination Chart for the International Geomagnetic Reference Field, 2005 (small)

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Magnetic Declination Chart for the International Geomagnetic Reference Field, 2005

Mv-world

USCGS Chart number 361 (1884)

Magnetic declination, also known as magnetic variation, is the angle on the horizontal plane between magnetic north (the direction the north end of a compass needle points, corresponding to the direction of the Earth's magnetic field lines) and true north (the direction along the Earth's surface towards the geographic North Pole). This angle varies depending on position on the Earth's surface and changes over time.

Overview

Magnetic declination is a critical factor in navigation, especially in the era before the widespread availability of global positioning systems (GPS). It allows for the correction of compass readings to point towards true north instead of magnetic north, which is essential for accurate navigation. The declination is positive when magnetic north is east of true north and negative when it is to the west.

Measurement and Representation

The value of magnetic declination is not constant, as the Earth's magnetic field changes due to geological and solar activities. It is measured in degrees and can be determined using a magnetic declination map, which is updated regularly to reflect changes in the Earth's magnetic field. These maps are produced by national geological agencies, such as the United States Geological Survey (USGS) and the British Geological Survey (BGS).

Causes of Variation

The Earth's core, composed of molten iron and nickel, generates the magnetic field that causes magnetic declination. The movement of this molten metal, along with the influence of the magnetic materials in the Earth's crust, contributes to the fluctuation of the magnetic field. Solar winds and the interaction between the Earth's magnetic field and the solar magnetic field can also cause short-term changes in magnetic declination.

Historical Significance

Historically, understanding and calculating magnetic declination was crucial for exploration and sea navigation. Notable explorers, including Christopher Columbus and James Cook, had to account for magnetic declination in their navigational calculations to ensure the accuracy of their voyages.

Practical Applications

Today, magnetic declination is essential for various applications beyond traditional navigation. It is crucial for aerospace navigation, geophysics, military operations, and even in civil engineering for accurately aligning structures in relation to the Earth's geographic coordinates.

Calculating Magnetic Declination

To calculate the current magnetic declination for a specific location, one can use online tools provided by geological agencies or refer to the latest magnetic declination maps. These tools often require the input of geographic coordinates (latitude and longitude) to provide the correct declination value.

Conclusion

Magnetic declination plays a vital role in navigation and various scientific fields. As the Earth's magnetic field continues to change, the importance of monitoring and understanding magnetic declination remains significant for accurate navigation and research.