[katieHaylor (OP)]

Darrin asks:

What's the difference between magnetic north and true north, as it relates to the weather and the movements of the constellations in the skies above?

Can you help/

[alancalverd]

The earth rotates around the true north axis. This wobbles a bit but generally points close to Polaris and all the other stars appear to rotate around it. Sadly there is no equivalent southern celestial reference.

The magnetic north pole wanders around and is currently somewhere under the Arctic ocean about 8 degrees off the true north, at 180 deg longitude.

The difference is pretty negligible for navigation in the British Isles as the offset between compass and true north is almost zero and is updated regularly on all air and sea charts. In fact is isn't much of a problem in any inhabited area this year, but  it was a significant problem in Alaska in the 1900s when the deviation between M and T was around 50 degrees!

At very high latitudes the aurorae, or at least the charged particle fluxes that cause them,  may have some influence but the effect on weather is fairly negligible outside of arctic regions as long as the magnetic pole remains inside the arctic circle. 

[charles1948]

When the North Magnetic Pole varies its position, does the South Magnetic Pole follow it correspondingly.

I mean, suppose the N.M.P shifts, say 1° westwards.  Does the S.M.P down below, shift 1° eastwards? 
Has that been observed to happen?

It seems to me, that it ought to happen.  To maintain electromagnetic balance between the two Poles.

Otherwise, if the Poles got out of balance,  mightn't that cause stress on the Earth's crust.  Possibly resulting in disturbances such as earthquakes?

[alancalverd]

The south magnetic pole is not diametrically opposite to the north, and whilst N_M has been moving closer to N_T for the last 100 years or so, S_M has actually been moving away from S_T.

The cause is a long way below the crust, which moves in all sorts of ways quite independently.

[evan_au]

I mean, suppose the N.M.P shifts, say 1° westwards.  Does the S.M.P down below, shift 1° eastwards?
 ...To maintain electromagnetic balance between the two Poles.

You are assuming that there are just two poles (a dipole)...
- It is true that for the past few thousand years, Earth's magnetic field has been dominated by two poles.
- But the strength of those two poles is weakening, which allows other effects to appear, like a "hole" in the magnetic field over the South Atlantic
- This hole dips down to an altitude of around 200km, which exposes satellites and the ISS to increased radiation, likely causing the loss of several satellites.
- And this weakness continues a downward trend.

Earth's magnetic field undergoes occasional random flips, where the dipole field disappears and reverses
- Presumably, during such a flip, auroras should be visible even at the equator
- There are suggestions that when the dipole field drops to zero, there might be a remnant quadrupole field, with two "North" magnetic poles and two "South" magnetic poles, located nowhere near the True North & South poles.

After the dipole pole flips, the Magnetic poles will be opposite the True poles.

See: https://en.wikipedia.org/wiki/South_Atlantic_Anomaly
https://en.wikipedia.org/wiki/Earth%27s_magnetic_field#Magnetic_field_reversals