Understanding the Difference Between True North and Magnetic North

When navigating with a compass or a map, it is essential to understand the difference between true north and magnetic north. As you move from one location to another, the disparity between these two points can become significant, especially for pilots, hikers, and sailors.

What is the Difference Between Magnetic North and True North?

True north is defined as the direction toward the northernmost point of the Earth's axis, which is the North Pole. The Earth rotates around this axis, and true north and true south are used as reference points for navigation in both water and air. To navigate using true north, you would need accurate clocks and the position of the sun, which can be challenging and not practical in many situations.

Magnetic north, on the other hand, is the point located near the Earth's magnetic poles. It is the area where a freely rotating magnetic needle on a compass aligns with the Earth's magnetic field. The magnetic north pole is not fixed and can vary over time. In many regions, including Illinois and Oregon, the magnetic north pole is significantly different from the true north pole.

Why Does It Matter for Pilots?

In regions with a significant magnetic declination, like my area, where the magnetic declination is -8.5 degrees, pilots must account for this difference to navigate correctly. This declination is shown on navigational maps as a dashed black line leaning 8.5 degrees to the right. The line is marked with -8.5 at regular intervals, indicating the necessary adjustments to make when using a compass.

To fly a heading using a compass, pilots must subtract the magnetic declination from the true heading. For example, if one wishes to fly due east (which would be a true heading of 90 degrees), they must subtract 8.5 degrees to get a compass heading of 81.5 degrees. This ensures that the aircraft will follow the correct path according to the true north.

The Impact of Magnetic Declination on Navigation

The difference between true north and magnetic north is caused by the Earth's magnetic field, which is not perfectly aligned with the Earth's axis of rotation. This misalignment creates a magnetic field that varies in intensity and direction from one location to another, leading to a phenomenon known as declination. In some regions, the magnetic field can be so strong that a compass needle will not point exactly north.

To navigate accurately, especially in aviation, sailors, and hikers, it is crucial to understand and account for this declination. For instance, if you are in Illinois, the magnetic declination is slightly different from the true north, and in Oregon, it is even more significant. This means that navigational maps in these regions will show a declination line and values specific to that area.

How Magnetic North and True North Relate to the Earth's Core

Magnetic north is not always aligned with the geographic north pole. It is influenced by the Earth's magnetic field, which is generated in the core. The Earth's magnetic field is complex and is constantly changing due to various factors, including geological processes and the movement of the Earth's core. This movement can cause the magnetic poles to wander over time, and even reverse their orientation.

In contrast, true north is a fixed point, representing the Earth's axis of rotation. Despite the constant change in the magnetic poles, true north remains a constant reference point. This stability makes true north an invaluable tool for navigation, especially in aviation and marine navigation.

Conclusion: Understanding the difference between true north and magnetic north is essential for accurate navigation. The magnetic declination can significantly impact your route, especially in regions far from true north. By accounting for this declination and using maps and compasses correctly, you can navigate more accurately and safely.