What is Magnetic Variation? | East is Least, West is Best

When you're navigating an aircraft, understanding magnetic variation is crucial. It's the subtle but important difference between true north and magnetic north that affects how you interpret your compass directions. Whether you're a student pilot or an experienced aviator, grasping this concept can significantly improve your navigation skills and ensure safe flights. In this article, we'll explore magnetic variation visually and practically, breaking down what it means, why it happens, and how to use it effectively when planning your flights.

Understanding True North vs. Magnetic North

Imagine you are standing on the ground at Independence State Airport in Oregon, looking at a map of the airport. The runway appears almost perfectly vertical on the map—straight up and down. This vertical line is not just a random alignment; it aligns closely with a line of longitude, which is an imaginary line running from the North Pole to the South Pole.

This runway is aligned straight up an down on a map, so it points to True North, but it is called Runway 34, not 36, because it is not aligned with Magnetic North, but is closer to 340°

Lines of longitude are crucial in navigation because they all converge at the True North Pole. This is the fixed point around which the Earth spins. If you looked at the Earth from above the North Pole, it would seem stationary while the Earth rotates beneath it. All lines of longitude, including the runway's centerline, point toward this True North Pole. If you could follow that runway centerline far enough, you'd eventually reach True North.

Zooming out, the runway is aligned with a line of longitude. All lines of longitude converge at the True North Pole

Why Does the Compass Not Point to True North?

Even though the runway points north on the map, your magnetic compass does not show a heading of 360 degrees (Magnetic North). Instead, it shows about 345 degrees, which is about 15 degrees off. This discrepancy arises because the compass aligns itself with the Earth’s magnetic field, not the geographic poles.

The Earth behaves like a giant magnet with magnetic field lines flowing through a point known as the Magnetic North Pole. This pole is close to, but not exactly at, the True North Pole. It moves slightly every year due to changes in the Earth's magnetic field. Currently, it is located near northern Canada, offset from the geographic pole.

So, when your compass points “north,” it is actually pointing toward the Magnetic North Pole, not the True North Pole. This difference between true north and magnetic north is what we call magnetic variation or magnetic declination.

Magnetic fields converge at the Magnetic North Pole, which is close to, but not exactly at the True North Pole

What is Magnetic Variation?

Magnetic variation is the angle between True North and Magnetic North. It varies depending on where you are on the Earth’s surface. Different locations will have different magnetic variations due to the irregularities in the Earth's magnetic field.

For example, near Independence State Airport in Oregon, the magnetic variation is about 15 degrees east. This means that Magnetic North is 15 degrees east of True North at that location.

Visualizing Magnetic Variation

To help visualize magnetic variation, imagine standing on the runway centerline facing True North (360 degrees). Your compass, however, will not point straight ahead but will show a heading of about 345 degrees. This is because the compass is aligned with Magnetic North, which is offset by 15 degrees to the east.

On sectional charts used for flight planning, you can often see dashed lines called isogonic lines. These lines connect points of equal magnetic variation. The line near Independence State shows a 15-degree east variation, confirming what we observe with the compass.

The closest isogonic line to Independence on the sectional is 15°E

How to Use Magnetic Variation in Navigation

When planning a flight, it's essential to adjust your headings to account for magnetic variation. If you are navigating using True North from your map but your compass points to Magnetic North, you need to convert between true headings and magnetic headings.

Converting True Course to Magnetic Course

Here’s a straightforward way to remember how to adjust for variation:

• East is least: If the variation is east, subtract it from the true heading.

• West is best: If the variation is west, add it to the true heading.

  
  

For example, if you want to fly a true course of 360 degrees and your variation is 15 degrees east, you subtract 15 degrees to get a magnetic course of 345 degrees. This magnetic course is what you would use to set your compass heading.

If the variation were west instead, you would add the variation to the true course. This mnemonic, “East is least, West is best,” is a handy memory aid to avoid confusion when calculating magnetic courses.

Navigation Beyond the Compass

Magnetic variation affects not only your compass but also other navigation aids. For instance, VOR (VHF Omnidirectional Range) stations, which are radio navigation aids, use magnetic directions rather than true directions. The compass rose displayed on VOR charts is aligned with magnetic north, not true north.

However, be cautious because these compass roses on sectional charts may not always be updated as frequently as isogonic lines. This means they might not perfectly reflect the current magnetic variation, so always cross-reference with the latest charts.

Magnetic Variation and GPS

Modern GPS units display tracks and courses based on magnetic directions, aligning with what your magnetic compass would show. For example, flying along the runway centerline at Independence, your GPS track will show approximately 345 degrees magnetic, matching your compass heading, not 360 degrees true.

This integration of magnetic variation into GPS navigation helps maintain consistency across all navigation instruments and aids.

Summary: Why Magnetic Variation Matters

Magnetic variation is a fundamental concept for pilots and navigators because it affects how headings are read and followed. Here’s a quick recap of the key points:

1. The Earth has two north poles: True North (geographic) and Magnetic North (magnetic).

2. Your compass points to Magnetic North, not True North, causing a difference called magnetic variation.

3. Magnetic variation varies by location and changes over time.

4. When planning flights, adjust your headings for variation using the rule: East is least, West is best.

5. Navigation aids like VOR stations and GPS also use magnetic directions.

   
   

By understanding and applying magnetic variation correctly, you ensure that your compass readings and navigational instruments align with your planned courses, reducing the risk of navigational errors.

Further Learning and Resources

For pilots and aviation enthusiasts eager to deepen their understanding of navigation and other flying essentials, there are plenty of resources available. Comprehensive training platforms like FlightInsight offer detailed courses and videos covering magnetic variation and much more.

Exploring sectional charts, practicing plotting courses with variation adjustment, and using flight simulators can also help solidify your grasp of how magnetic variation impacts real-world flying.

Remember, accurate navigation is a cornerstone of safe aviation, and mastering magnetic variation puts you one step closer to becoming a confident and competent pilot.

Happy flying, and keep your compass calibrated!