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Compass Variation Formula - Understanding Magnetic Declination

Compass variation, also known as magnetic declination, is a crucial concept in navigation and orientation. It refers to the angle between true north (geographic north) and magnetic north (the direction a compass points).

What Causes Compass Variation?

The Earth's magnetic field is not uniform and is generated by the movement of molten iron in the outer core. This results in variations in magnetic field strength and direction across the globe. Consequently, a magnetic compass doesn't always point directly to the geographic north pole.

Calculating Compass Variation

The compass variation at a specific location can be calculated using the following formula:

Magnetic Declination (θ) = Magnetic North - True North

In this formula:

  • Magnetic Declination (θ): The angle between true north and magnetic north, measured in degrees east or west. East declinations are positive, while west declinations are negative.
  • Magnetic North: The direction a magnetic compass points at the location of interest.
  • True North: The direction towards the North Pole.

Using Compass Variation in Navigation

Understanding and accounting for compass variation is essential for accurate navigation. When using a magnetic compass for navigation, you must apply the appropriate magnetic declination correction to convert magnetic bearings into true bearings.

Obtaining Magnetic Declination Information

Magnetic declination values vary depending on your location. To find the magnetic declination for a specific area, you can:

  • Consult nautical charts or topographic maps, which often provide declination information.
  • Use online tools or mobile apps that offer real-time magnetic declination values based on your GPS coordinates.
  • Refer to government agencies or geological surveys that publish declination data for various regions.

Compass variation, or magnetic declination, is a critical factor in accurate navigation. Understanding the concept and applying the appropriate correction ensures that your compass readings align with true north, helping you navigate safely and effectively.