🧭Earth’s Magnetic Field & Aurora - Declination, Magnetosphere, Kp Oval

How to use Earth’s Magnetic Field & Aurora (Dipole, Declination, Van Allen Belts)

1. 1In "Field & compass", pick a city or tap the map to read declination, inclination and field strength
2. 2In "Magnetosphere & Van Allen belts", set solar wind density, speed and Bz to see where the magnetopause sits
3. 3In "Trapped particles", choose energy, L-shell and pitch angle to watch bouncing and drift
4. 4In "Aurora & Kp", move Kp and UT to see the oval and the Kp each city needs
5. 5In "Pole drift & reversals", view the pole path, the falling dipole moment and the polarity timeline

FAQ

What is declination, and why does it differ from my phone?

Declination is the angle between magnetic north (where a compass points) and true north, positive to the east. This tool uses the simplest tilted dipole, which captures only about 90% of the field. The non-dipole rest can shift real declination by more than ten degrees: Beijing gets +2° from the dipole but about −8° in reality. Navigation and surveying use the World Magnetic Model or IGRF, which include spherical harmonics past degree 12 and are updated every five years.

How does inclination change with latitude?

For a dipole, inclination I and geomagnetic latitude λ satisfy tan I = 2 tan λ. On the magnetic equator a needle lies flat; it dips more steeply toward the poles and points straight down at the dip pole. The total field grows from about 30 µT at the equator to about 60 µT near the poles. Compasses made for mid-latitudes carry a small counterweight to stop the needle tilting.

What Kp do I need to see the aurora?

The night-side edge of the auroral oval sits near geomagnetic latitude 66.5° − 2°×Kp. At 55° geomagnetic you need about Kp 6 for aurora overhead, and one or two steps less to catch it low on the northern horizon. Much of the northern US and UK sits at 50°–55° geomagnetic. Northern China is only in the 30s, so it takes a Kp 9 storm with high red aurora, like May 2024. The tool lists the geomagnetic latitude and required Kp for many cities.

Why don’t particles in the Van Allen belts fall out?

A charged particle spirals along a field line, and its magnetic moment is nearly conserved. As the field strengthens toward the poles, parallel speed is converted into perpendicular speed until the particle stops and reflects: a magnetic mirror. It therefore bounces between two mirror points while gradient and curvature drift carry it around Earth, electrons east and protons west. Only particles with pitch angles inside the loss cone reach the atmosphere, where they are absorbed and make aurora.

Will the magnetic poles flip, and is it dangerous?

The field has reversed hundreds of times. The last full reversal was about 773,000 years ago, and the average spacing is a few hundred thousand years but very irregular. The north magnetic pole has drifted toward Siberia at 40–55 km per year in recent decades, and the dipole moment is falling about 5% per century, but that does not mean a flip is imminent. Reversals take thousands of years, the fossil record shows no link to mass extinctions, and the main effect would be more space-weather trouble for satellites and power grids.