magnetic declination

magnetic declination (countable and uncountable, plural magnetic declinations)

1. The horizontal angle between magnetic north and true north at a given place
   • 2002, Walter A. Schroeder, Opening the Ozarks: A Historical Geography of Missouri's Ste. Genevieve District 1760-1830, footnote, page 159,

     In the Ste Genevieve District, magnetic declination varies significantly within short distances due to iron-rich bedrock, and this might account for magnetic declinations varying from five to ten degrees east in Soulard's surveys.

   • 2002, Michael Windelspecht, Groundbreaking Scientific Experiments, Inventions, and Discoveries of the 17th Century, page 149,

     By the 17th century several instruments had been designed to measure the magnetic declination.

   • 2005, Phil Medina, Homework Helpers: Earth Science, page 53,

     This is corrected by setting the magnetic declination of the compass. This is a correction value given on all navigation maps. Once set with the magnetic declination, a compass will point to the true North Pole also known as the “Geographic North Pole." All places on Earth have a slightly different magnetic declination depending on how you line up with both poles. In an extreme case, if you stood between the two poles and faced the real North Pole, your masgnetic compass would point to the magnetic North Pole behind you—a magnetic declination of 180 degrees!

In nautical and aeronautical navigation, the term magnetic variation is used instead of magnetic declination and the angle is termed variation of the compass or magnetic variation. Magnetic declination is not otherwise synonymous with magnetic variation, which refers to regular or irregular change with time of the magnetic declination, dip, or intensity.[1]

• magnetic inclination
• magnetic meridian
• magnetic variation
• isogonic line
• agonal line