Magnetic North vs True North: The Shocking Difference!
Navigation relies heavily on understanding the difference between magnetic north and true north. True North, a fixed point defined by the Earth's rotational axis, provides a stable reference. The magnetic compass, a tool dependent on Earth's magnetic field, points instead towards Magnetic North, a location that constantly shifts. The fluctuation in position of magnetic north is monitored by organizations such as NOAA (National Oceanic and Atmospheric Administration). These factors all contribute to the critical need to consider declination when using maps, especially in areas with substantial angular difference between magnetic north and true north.
Image taken from the YouTube channel ScienceWorld , from the video titled Geographic (True) North vs Magnetic North .
Navigating the Compass: Understanding the Difference Between Magnetic North and True North
The difference between magnetic north and true north is a crucial concept for anyone using a compass for navigation, whether hiking, sailing, or simply exploring. Ignoring this difference can lead to significant errors in direction and potentially getting lost. Let's break down what each term means and why the distinction matters.
What is True North?
True North is the direction that points directly towards the geographic North Pole, which is the northern point of Earth's axis of rotation. This point is fixed and serves as a consistent reference for all maps and navigational systems.
Significance of True North:
- Fixed Point: True North remains constant and does not change over time.
- Map Accuracy: Maps are designed based on True North. Directional references on maps are generally aligned with it.
- Reliability: True North provides a dependable and universal point of reference for global navigation.
What is Magnetic North?
Magnetic North is the direction that a compass needle points towards. It is influenced by Earth's magnetic field, which is generated by the movement of molten iron within the Earth's core. The location of Magnetic North is not fixed and slowly drifts over time and space. Currently, it is located in the Canadian Arctic.
Variability of Magnetic North:
- Dynamic Location: The position of Magnetic North is constantly changing due to fluctuations in Earth’s magnetic field.
- Compass Dependency: Compasses align themselves with the Earth's magnetic field, thus pointing towards Magnetic North.
- Local Magnetic Anomalies: Local variations in the Earth's crust can also cause compass deviations away from the general Magnetic North direction. These are usually small, but important near iron deposits.
The Key Difference Between Magnetic North and True North: Declination
The "difference between magnetic north and true north" is known as magnetic declination (sometimes called magnetic variation). Declination is the angle between True North and Magnetic North at a given location. This angle varies depending on your geographic location and, because Magnetic North is always moving, it also changes over time.
Understanding Declination:
- Angular Measurement: Declination is measured in degrees, either east or west. East declination means Magnetic North is east of True North, while west declination means Magnetic North is west of True North.
- Location-Specific: Declination values differ significantly from place to place. For instance, the declination in London, UK will be substantially different than the declination in Denver, Colorado, USA.
- Time-Sensitive: Declination values change over time, often by a few minutes of arc (a fraction of a degree) per year. This change is gradual but necessitates periodic updates to declination information.
How Declination Affects Navigation:
- Compass Accuracy: If you are navigating using a compass and a map (which references True North), you need to account for declination. Failure to do so can lead to significant navigation errors.
- Declination Adjustment: To use a compass accurately with a map, you must add or subtract the declination value to convert between magnetic bearings (compass readings) and true bearings (map directions). Whether to add or subtract depends on whether the declination is east or west.
- Importance of Up-to-Date Information: Always use the most current declination value for your location. Many maps and online resources provide updated declination information.
Methods for Determining and Applying Declination
Several resources are available to help you determine the declination in your area and how to use it.
Resources for Finding Declination:
- Topographic Maps: Many topographic maps include a declination diagram, showing the declination value for the map's publication date.
- Online Calculators: Websites and apps offer declination calculators. These tools use your GPS coordinates to provide an up-to-date declination value.
- Navigation Apps: Many smartphone navigation apps automatically adjust for declination when using a compass.
- NOAA Website: The National Oceanic and Atmospheric Administration (NOAA) provides declination calculators and resources.
Correcting for Declination:
The rule to remember is:
- When converting a True Bearing (from a map) to a Magnetic Bearing (for your compass): Add East declination, Subtract West declination.
- When converting a Magnetic Bearing (from your compass) to a True Bearing (for your map): Subtract East declination, Add West declination.
Alternatively, you can adjust your compass so that the compass card is aligned to true north rather than magnetic north.
Example Scenario:
Suppose you are in an area with a declination of 5° East. You are using a map to navigate.
- Map to Compass: You want to follow a true bearing of 90° (East) from the map. To determine the corresponding compass bearing, you add the East declination: 90° + 5° = 95°. Therefore, you would follow a magnetic bearing of 95° on your compass.
- Compass to Map: You take a compass bearing of 180° (South). You need to convert this to a true bearing for your map. Since the declination is 5° East, you subtract it: 180° - 5° = 175°. Therefore, the true bearing is 175°.
Importance of Understanding Magnetic Declination
Failing to account for magnetic declination can have serious consequences, especially in situations where accurate navigation is critical.
Potential Consequences of Ignoring Declination:
- Navigation Errors: Small errors in declination can compound over distance, leading to significant deviations from the intended course.
- Getting Lost: In remote areas or challenging terrain, even a small navigational error can result in becoming lost.
- Safety Risks: In emergency situations, accurate navigation is crucial for reaching safety or rescue points.
Video: Magnetic North vs True North: The Shocking Difference!
FAQs: Magnetic North vs True North
Still scratching your head about magnetic north and true north? These frequently asked questions can help clear things up.
What exactly is the difference between magnetic north and true north?
True north is the fixed point on Earth's geographic North Pole, where all lines of longitude converge. Magnetic north, on the other hand, is the direction a compass needle points, influenced by Earth's magnetic field. The difference between magnetic north and true north creates what's called magnetic declination.
Why does the location of magnetic north change?
Unlike true north, which remains fixed, magnetic north is constantly shifting because the Earth's magnetic field is generated by the movement of molten iron in its core. This shifting causes the difference between magnetic north and true north to vary over time and location.
How important is it to account for the difference between magnetic north and true north?
For casual hikers, the difference might be negligible, especially with short distances and modern GPS tools. However, for precise navigation, like surveying, aviation, and long-distance wilderness travel using a map and compass, accounting for the difference between magnetic north and true north is crucial to avoid significant errors.
Where can I find the current magnetic declination for my location?
Many resources can help you find the current magnetic declination. Topographic maps often include declination diagrams. You can also use online magnetic declination calculators or consult navigational apps on your smartphone that provide real-time declination data. Knowing this difference between magnetic north and true north is key to accurate navigation.