Definition

Noun: 1. The angular difference between magnetic north and true north: This term refers to the angle, measured in degrees, between the direction indicated by a compass needle (magnetic north) and the direction of the geographic North Pole (true north) at a specific location on Earth. This difference is also commonly called magnetic declination.

Usage

• Magnetic variation is a critical concept in navigation, cartography, and surveying. It is used to correct compass readings to obtain true directional bearings.
• The value of magnetic variation changes depending on geographic location and slowly changes over time.

Examples

• Noun:
  • Before plotting the course on the map, the pilot had to account for the magnetic variation.
  • The magnetic variation in Seattle is approximately 15 degrees east.
  • Topographic maps usually include a diagram showing the local magnetic variation.

Advanced Usage

• Annual change: Magnetic variation is not constant; it changes annually due to shifts in the Earth's magnetic field. Maps and nautical charts often note the annual rate of change (e.g., "annual decrease 8' W").
• Isogonic lines: On maps, lines connecting points of equal magnetic variation are called . The line where the variation is zero is called the .

Variants and Related Words

• Magnetic declination: This is a direct synonym for magnetic variation and is the more technically precise term used in geodesy and cartography.
• Declination: In this specific navigational context, "declination" is often used interchangeably with "magnetic variation."
• Compass variation: Another less common synonym.

Synonyms

• Magnetic declination
• Declination (in navigational context)
• Compass variation

Related Phrases

• Correcting for variation: The process of applying the magnetic variation value to a compass bearing to find a true bearing, or vice-versa.
  • Example: Remember to correct for variation when converting your compass course to a true course on the chart.

Noun

1. the angle (at a particular location) between magnetic north and true north