Lines around a magnet
What the invisible area around a magnet looks like.
What you are looking at
The dots arrange themselves into curved lines that loop from one point to another, like the lines you get with iron filings around a magnet.
The idea
Put a sheet of paper on a bar magnet and sprinkle iron filings on it. The filings line up into curved lines, running out of one end of the magnet and looping around into the other end.
The magnet has a push-and-pull zone around it, even though you cannot see it. Each tiny filing turns to point along the push in its spot, so together they draw the shape of the zone.
The dots in the animation do the same job. They are not making the pattern. They are just showing where the pattern already is.
Where else you see it
- A compass needle lines up with the lines of the Earth, which acts like a very large bar magnet.
- The magnet on your fridge.
- The Sun and many planets and stars have the same overall shape of magnetic zone.
Go deeper: the proper names and the math
The animation shows a magnetic dipole. Field lines of a dipole follow r = r₀ sin²θ in spherical coordinates, where θ is measured from the magnetic axis. Field strength falls with distance as 1/r³.
Magnetic field lines have no beginning or end (∇·B = 0), so they always form closed loops, passing through the magnet. Earth's field is roughly a dipole, tilted about 10° from the spin axis, and the solar wind stretches it into a long tail on the night side.