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🧭 How does a compass work near the poles?

Your needle is not pointing at a place. It is reporting the direction of the magnetic field in the few centimetres of air around it — and near the poles that field turns vertical, so the sideways part a flat needle needs falls away to nothi

4
lessons
~20 min
to learn
🔬 Science
subject
Adults
level
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What you’ll learn

  1. What the needle is actually doingExplain that a compass aligns with the horizontal part of the local geomagnetic field, and say where that field comes from.The needle reports a direction at one point in space, not the bearing of a distant place — and the field it reports is made by moving iron in Earth's outer core, which is why it changes.
  2. Three norths, and which one your needle knowsDistinguish true, grid and magnetic north, and distinguish the geographic, geomagnetic and magnetic dip poles.Three norths and three kinds of pole answer three different questions; only magnetic north is the one a needle can give you, and only the dip poles are where the field actually stands on end.
  3. What fails as you go polewardExplain magnetic inclination and show why a flat compass loses its heading as the horizontal field strength falls.The field tilts toward vertical and the horizontal component collapses; NOAA marks the result on its charts as caution and blackout zones, and at a dip pole declination is undefined rather than merely large.
  4. How navigators cope, and where the pole is goingDescribe balancing zones, the limits of non-magnetic backups, and how a wandering pole forces the field models to be reissued.Engineering can fix a dragging needle but not a missing horizontal field, gyrocompasses fade toward the poles too, and the pole's own motion means every declination figure carries a date.

Questions this course answers

What is a compass needle actually responding to?

A field is a direction defined at every point in space. The needle turns until it lies along the horizontal part of the field where it happens to be — it has no information about anywhere else.

Where does most of the field a compass feels come from?

NOAA puts more than 90 percent of the measured field down to internal sources in the outer core. Because the fluid is moving, the field it makes changes — which a permanent magnet could never do.

Magnetic declination is the angle between…

The USGS defines it as "the deviation of the compass from true north", and says it varies with both geographic location and time.

Which pair of poles is guaranteed to be exactly opposite each other on the globe?

The geomagnetic poles come from fitting one dipole to the field, so they are antipodal by construction. NOAA says the dip poles "do not need to be (and are not currently) antipodal" — for 2025.0 they sit at 85.762°N, 139.298°E and 63.851°S, 135.078°E.

What is grid north?

Grid north belongs to the paper, not the planet: it is where the map projection's vertical lines run. That is why polar grids abandon longitude above 84°N and lay a flat square grid over the pole instead.

Why does an ordinary compass stop giving a usable heading near a magnetic pole?

The total field near the pole is strong — Earth's surface field runs about 22,000 to 67,000 nT. It is the sideways part, the only part a flat needle can use, that collapses as the field turns vertical.

Grounded in trusted sources

  • NOAA National Centers for Environmental Information, "Geomagnetism Frequently Asked Questions" — https://www.ncei.noaa.gov/products/geomagnetism-frequently-asked-questions
  • NOAA NCEI, "World Magnetic Model Accuracy, Limitations, and Error Model" — https://www.ncei.noaa.gov/products/world-magnetic-model/accuracy-limitations-error-model
  • NOAA NCEI, "Wandering of the Geomagnetic Poles" — https://www.ncei.noaa.gov/products/wandering-geomagnetic-poles
  • NOAA NCEI, "World Magnetic Model (WMM)" — https://www.ncei.noaa.gov/products/world-magnetic-model
  • NOAA NCEI, "World Magnetic Model Out-of-Cycle Release", 4 February 2019 — https://www.ncei.noaa.gov/news/world-magnetic-model-out-cycle-release
  • U.S. Geological Survey, "What is declination?" — https://www.usgs.gov/faqs/what-declination
  • British Geological Survey, "An Overview of the Earth's Magnetic Field" — https://geomag.bgs.ac.uk/education/earthmag.html
  • British Geological Survey, "'Three norths' set to leave England and not return for hundreds of years" — https://www.bgs.ac.uk/news/three-norths-set-to-leave-england-and-not-return-for-hundreds-of-years/

Every Wunder lesson is built from real, reputable sources — never invented.

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