On a prairie, a compass points north — no magnet for miles. What turns the needle?
On a clear night near the Arctic, the sky ripples with green light: the northern lights. The same show almost never appears over the equator. Why the poles?
Two facts you already have do the work. Earth has its own magnetic field, shaped like a bar magnet's. And a moving charged particle in a magnetic field feels a force, unless it moves parallel to the field lines.
The Sun constantly throws out streams of charged particles. The particles fly toward Earth, moving through Earth's magnetic field.
They are charged and moving, so the field exerts forces on them. The forces deflect the particles: they cannot simply cut across the field lines.
Deflected again and again, the particles end up guided along the field lines. Earth's field lines come down to Earth near its two magnetic poles, so the guided particles come down near the poles.
There they crash into the gas of the upper atmosphere. The crashes make the gas glow. That glow is the aurora.
Earth's magnetic field deflects the Sun's charged particles. Where do they come down?
Why can Earth's magnetic field deflect the Sun's particles at all?
A stream of charged particles from the Sun reaches Earth's magnetic field. Where does the stream end up, and why there?
The particles are charged and moving, so Earth's field deflects them.
Deflected, they travel along the field lines instead of cutting across them.
The field lines come down near Earth's magnetic poles.
The stream is guided down near the poles. That is why the aurora appears there.
What makes the aurora's light?
Which statement explains why the aurora appears near the poles?
Another planet has a magnetic field shaped like a bar magnet's. Charged particles stream past it. Where would that planet's aurora most likely appear?
What does Earth's magnetic field do to the incoming charged particles?