The north pole is the top of the earth, and the south pole is the bottom, of course...
except that the earth is kind of a ball, and they don't really have tops and bottoms.
Granted, the earth isn't exactly spherical and it's spinning through space - spinning
about an imaginary axis of rotation.
One of the points where that axis goes through the earth, right here in the arctic ocean,
where the Russians planted their flag on the sea floor in 2007, is called the north pole...
or rather, it's the "geographic" north pole.
Because, just like there are different definitions for what a "year" is, there are different
north poles.
For example, compasses don't point to the geographic, or spinning-top, north pole.
They point to the MAGNETIC north pole, which is incidentally a magnetic south pole since
opposites attract.
The magnetic north (actually south) pole and south (actually north) pole are an electromagnet
caused by swirling convection currents in the earth's liquid iron outer core.
These currents are heavily influenced by the rotation of the earth, so the magnetic field
they generate roughly aligns with the earth's axis of rotation - but not precisely, and
not unchangingly.
A hundred years ago, the magnetic north pole was located in northern canada - over 2000km
south of the geographic north pole.
And it's been moving consistently north-west since then, currently sitting in the middle
of the Arctic Ocean 450km south of the geographic north pole, and drifting about 55 kilometers
closer to Russia each year.
What's more, the magnetic south pole is not on the exact opposite side of the earth from
the magnetic north pole - it drifts around in a somewhat independent fashion and is currently
20° closer to the equator than magnetic north!
Such is the nature of magnetic fields generated by confusingly swirly molten iron deep inside
the earth.
But if you imagined, instead, that there were just a giant, perfect bar magnet inside the
earth, then that perfect bar magnet would point towards the GEO-magnetic north pole.
Which is currently located in Ellesmere Island, Nunavut, Canada.
This pole, together with the geomagnetic south pole which IS on the exact opposite side of
the earth, represents the general, overall trend of the earth's magnetic field, especially
as it extends into space.
So while it's not at all useful for compass navigation on the earth's surface, it does
heavily influence the paths of solar wind particles that cause the aurora - that is,
the northern lights.
Beautiful.
In short, the north pole's whereabouts depend on what you care about.
The earth spins like a top around the "geographic" north pole, compasses point to the "magnetic"
north pole (which is actually a magnetic south pole), and the northern lights are strongest
in a ring around the "geomagnetic" north pole (also a magnetic south pole).
All three north poles move, too - the magnetic and geomagnetic poles change quite drastically,
but even the geographic north pole moves up to ten meters a year as the earth wobbles
on its axis due to seasonal air pressure differences across the globe, melting ice caps, and so
on.
Assuming that the Russians planted their flag exactly at the geographic north pole in August
2007, not once since then has it been exactly at the pole - it was as far as 12 meters away
in 2009 and as close as 20 cm in 2010 - right now it's about 3 and a half meters away.
Basically, the earth is doing the biggest, slowest, pole dance ever around the Russian
flag.