1. What is Magnetic Declination?

Magnetic declination is the angle between magnetic north (the direction the compass needle points) and true north (the direction along the Earth's surface towards the geographic North Pole). This angle varies depending on your location and changes over time.

2. How Does the Calculator Work?

The calculator uses the International Geomagnetic Reference Field (IGRF) model:

Where:

• \( \text{Latitude} \) — Geographic latitude (-90° to 90°)
• \( \text{Longitude} \) — Geographic longitude (-180° to 180°)
• \( \text{Year} \) — Year of interest (1900 to present)

Explanation: The IGRF model uses spherical harmonic coefficients to calculate the geomagnetic field components at any point on or above the Earth's surface.

3. Importance of Magnetic Declination

Details: Accurate declination values are crucial for navigation, surveying, and any application requiring precise orientation. The magnetic poles drift over time, making historical calculations important for understanding past measurements.

4. Using the Calculator

Tips: Enter latitude and longitude in decimal degrees (positive for north/east, negative for south/west). The year must be between 1900 and the current year.

5. Frequently Asked Questions (FAQ)

Q1: How often does magnetic declination change?
A: Declination changes continuously, though the rate varies by location. The IGRF model is updated every 5 years.

Q2: What's the difference between declination and inclination?
A: Declination is the horizontal angle between magnetic and true north, while inclination (or dip) is the vertical angle between the magnetic field and the horizontal plane.

Q3: Why does declination vary by location?
A: The Earth's magnetic field is complex and irregular, with the magnetic poles offset from the geographic poles.

Q4: How accurate is the IGRF model?
A: The IGRF is generally accurate to within 30 minutes of arc (0.5 degrees) for recent years, with decreasing accuracy for older dates.

Q5: Can I calculate future declination?
A: The IGRF includes a predictive component, but accuracy decreases for dates more than 5 years in the future.