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 USGS geomagnetic models to compute declination:

Where:

• Latitude — Your location's latitude (-90° to 90°)
• Longitude — Your location's longitude (-180° to 180°)
• Date — The date for which to calculate declination
• Model — The geomagnetic model used (WMM or IGRF)

Explanation: The USGS models incorporate data from satellites and ground observatories to predict the Earth's magnetic field.

3. Importance of Magnetic Declination

Details: Accurate declination values are essential for navigation, surveying, and any activity requiring precise orientation. Ignoring declination can result in significant navigation errors.

4. Using the Calculator

Tips: Enter your exact coordinates in decimal degrees. The date should be within the valid range of the selected model (WMM: 5-year epochs, IGRF: longer periods).

5. Frequently Asked Questions (FAQ)

Q1: How often does magnetic declination change?
A: Declination changes gradually over time, typically a few minutes per year, but this varies by location.

Q2: Why are there different geomagnetic models?
A: WMM is optimized for navigation and updated every 5 years. IGRF covers longer time spans and is used for scientific research.

Q3: How accurate are these calculations?
A: Typically accurate to within 30 minutes of arc, but local magnetic anomalies can cause greater errors.

Q4: Does elevation affect declination?
A: Yes, but the effect is usually small compared to horizontal position and date.

Q5: How far back can I calculate declination?
A: IGRF provides models back to 1900, while WMM only covers recent epochs.