Why We Use Magnetic North and Not True North on the Compass

At first glance, the Earth's true north might seem like the perfect direction to use for navigation. However, the reality of navigating using a compass introduces a few challenges associated with the natural phenomena of magnetic north. This article explores why magnetic north is the preferred direction for many navigation techniques, despite the existence and importance of true north.

Understanding True North and Magnetic North

True north is the direction of the Earth's axis of rotation. It's like the shaft of a top, the core axis around which the planet spins. Magnetic north, on the other hand, is determined by the Earth's magnetic field, which is generated by the iron core and its slow-moving convection currents. This magnetic field does not align with Earth's axis, leading to variations in magnetic north.

It's important to note that the magnetic poles do not correspond exactly to the geographic poles. The Earth's magnetic poles wander, often deviating hundreds of kilometers from their locations over time. Additionally, the geographic poles are not exactly opposite each other due to the Earth's non-spherical shape. Consequently, the magnetic and true norths can differ significantly, particularly in certain geographical areas.

Navigating with Magnetic North

One of the primary reasons magnetic north is extensively used in navigation is historical and practical. For example, aviation relied on magnetic compasses before the invention of gyrocompasses, which are more accurate but require power. Magnetic compasses, powered only by the Earth's magnetic field, are simple, reliable, and don't need any external power. Pilots can still rely on their trusty magnetic compass in emergency situations.

Resorters to ground-based navigation such as hikers and canoeists use magnetic compasses similarly. They may convert their directions to true north when necessary, particularly in regions with established grid systems and known magnetic variations. This allows for more precise navigation, especially in areas with significant magnetic variations.

Magnetic Variation Explained

Magnetic variation, or magnetic declination, is the angle between magnetic north and true north. It varies depending on the location on Earth's surface. Observing the North Star (Polaris) can help determine magnetic variation. In the northern hemisphere, aligning a stick or two rocks can give a visual indication of the angle. In the southern hemisphere, the lack of a South Star makes this method less practical.

Navigating with Both Magnetic and Grid North

Navigating with a compass involves more than just magnetic variation. Grid north is the true north aligned with the geographic grid system. Understanding the relationship between magnetic north and grid north is crucial. The grid-magnetic angle can be used to adjust your magnetic bearing to grid bearing. This angle varies with location and time, making it essential to record your position-specific data in advance.

For instance, on Great Gable, a challenging mountain in the English Lake District, navigating while in poor weather becomes a real challenge. Without proper tools and data, deciding the correct path can be treacherous. A compass with both magnetic and grid compasses, along with a map, simplifies the process. By aligning the compass's red lines with the map's grid lines, you can measure the grid bearing accurately.

Tools and Techniques for Navigation

Modern navigation tools like fiber-optic ring gyroscope and mains power supply-based navigational systems are powerful but not always practical for hikers. A lightweight, easy-to-use compass remains a reliable tool for outdoor navigation. With a few simple steps, you can account for magnetic variation and grid bearing, ensuring you stay on the right path.

The compass's dial can help you find the correct bearing. Setting the compass on the map, aligning the long side with your path, and using the dial to align the red lines with the grid lines allows you to read the grid bearing. However, without a method to point to grid north, this information is not directly useful.

To convert the grid bearing to a magnetic bearing, you need to apply the grid-magnetic angle. This adjustment simplifies navigation on the ground. By knowing the angle, you can add or subtract it from your grid bearing to get the magnetic bearing, which the compass can then point towards.

Using a compass and map together, you can plan and follow your route with precision. Modern tools and careful planning ensure safer and more efficient navigation. Understanding the nuances between magnetic north, true north, and grid north is crucial for reliable outdoor navigation.

Keywords: magnetic north, true north, compass navigation