True North and Magnetic North – Know the Difference

Knowing the difference between true north and magnetic north is crucial for accurate orientation and navigation. Maps and GPS rely on true north, while a compass shows magnetic north. There are other important distinctions, too.

Key Points: True North vs Magnetic North

• True north refers to the geographic North Pole and is fixed.
• Magnetic north aligns with Earth’s magnetic field and shifts over time.
• Magnetic variation is the angular difference between true and magnetic north.
• True north and magnetic north rarely align, but it does happen.

What Is North?

“North” is the direction along Earth’s surface towards the North Pole, the northernmost point of the planet. Another way of looking at it is that north is to the left of east (the direction of sunrise). However, there are two types of north: true north and magnetic north. True north or geographic north depends on the Earth’s rotational axis, while magnetic north depends on Earth’s magnetic field. Additionally, the geomagnetic north pole adds another layer of complexity to Earth’s magnetic system.

Definitions and Locations

Understanding the precise definitions and locations of true north, magnetic north, and geomagnetic north is key to grasping their differences and applications in navigation and mapping.

• True North: This is the direction pointing toward Earth’s geographic North Pole, where the planet’s rotational axis meets the surface in the Northern Hemisphere. True north remains constant over time.
• Magnetic North: This is the direction that a magnetic compass needle points, which aligns with Earth’s magnetic field. Magnetic north is at the magnetic north pole, which moves due to changes in Earth’s molten core. As of recent measurements, the magnetic north pole is near 86.5°N, 164.0°E in the Arctic Ocean. It is moving northwest at approximately 40-60 kilometers per year.
• Geomagnetic North: This is the point where Earth’s idealized magnetic field (modeled as a dipole) intersects the planet’s surface. The geomagnetic north pole is near 80.65°N, 72.68°W in Canada. It moves more slowly than the magnetic north pole and serves as a reference in studies of Earth’s magnetic field and space weather.

Significance and Uses

Both true and magnetic north serve important functions:

• True North: Essential for precise navigation, astronomy, and geodesy. Maps and GPS systems align with true north.
• Magnetic North: Critical for compass-based navigation and when navigating without electronic aids.

Comparison Table: True North vs Magnetic North

The following table provides a quick reference to compare the key features of true north and magnetic north.

Magnetic Variation

The angle between true north and magnetic north at a specific location is called magnetic variation or declination. For example, if true north is 0° and magnetic north is at 5° east, the magnetic variation is +5° east. Navigators subtract 5° from their compass reading to align it with true north. Conversely, if magnetic north is 5° west, the variation is -5°, and they add 5° to align their reading.

• East Variation: Occurs when magnetic north is east of true north.
• West Variation: Occurs when magnetic north is west of true north.

Magnetic variation changes depending on geographic location and shifts over time as the magnetic north pole migrates. An agonic line is an imaginary line on the Earth’s surface that has no magnetic declination. Currently, an agonic line passes through parts of the Gulf of Mexico and runs toward the Arctic. Navigators in these regions experience no angular difference between true and magnetic north.

Having true north (geographic North Pole) and magnetic north at the exact same physical point is an extremely unlikely event. It has not occurred in recorded history and would require Earth’s magnetic field and rotational axis to align perfectly, which is unlikely given the dynamics of Earth’s core.

How to Find True North Without Instruments

You can find true north without instruments by using natural methods:

• Using the Sun: In the Northern Hemisphere, observe the sun at solar noon (when it is at its highest point in the sky). The shadow cast points directly north.
• Using the Stars: Locate Polaris, the North Star, which sits nearly directly above the geographic North Pole.

Finding Magnetic North Without a Compass

You can find magnetic north without a compass by observing magnetic materials. For example:

• Using a Makeshift Compass: Magnetize a needle (or other thin steel object) by rubbing it on a magnet or silk, then float it on water using a leaf or cork. The needle aligns with the magnetic field, pointing toward magnetic north and south. Magnetic north is in the same general direction as geographical north, so use the sun or stars for identifying north from south.

Common Misconceptions

• Misconception: True north and magnetic north are the same.
  • Reality: They are distinct and rarely align.
• Misconception: Magnetic north is fixed.
  • Reality: Magnetic north moves annually due to changes in Earth’s core.
• Misconception: Compasses always point to true north.
  • Reality: Compasses point to magnetic north.

FAQs

• Can you use magnetic north for GPS navigation? A: No, GPS systems rely on true north for precise calculations.
• How much does magnetic north move annually? A: Magnetic north shifts approximately 10-60 kilometers per year.
• How do I find true north without a GPS? A: Use a compass and adjust for local magnetic variation.
• Are magnetic and geographic poles opposite? A: Not necessarily; they move independently. The north and south geographic poles are on opposite sides of the planet from each other. So are the north and south magnetic poles. But, every so often, the magnetic poles flip, so the north magnetic pole becomes the south magnetic pole and vice versa!

References

• Archinal, Brent A.; A’Hearn, Michael F.; et al. (2010). “Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2009”. Celestial Mechanics and Dynamical Astronomy. 109 (2): 101–135. doi:10.1007/s10569-010-9320-4
• Bowditch, Nathaniel (2002). American Practical Navigator. Paradise Cay Publications. ISBN 9780939837540.
• Jian, Baruch, Li, John (2011). “Can you find south using your watch?”. Astronomy & Geophysics. 52 (3): 3.12 – 3.14. doi:10.1111/j.1468-4004.2011.52312.x