I Questions about planetary magnetic fields

1. Sep 10, 2017

Hawksteinman

1. Why is Earth's South Pole called its North Pole? Why hasn't it been changed to make it more scientifically accurate?

2. Why are the North Poles of other planets defined relative to Earth's 'North' Pole? Why isn't it based upon the actual direction of the planet's magnetic field?

2. Sep 10, 2017

To answer question #1, I believe the answer is the north pole of a magnet follows the convention of the magnetic needle of a compass. The north pole of the magnet, when on the surface of earth (at least in most places) will be the end that points north. This is also designated as the + pole. It's own magnetic field will go from the + end to the - end outside the compass needle. It turns out, for the iron that makes up the earth's magnetic field inside the earth, in order for the earth's magnetic field to point north outside the earth and align the compass needle, it actually has its + pole inside the earth in the southern hemisphere. To follow the convention of the compass needle, that is the north magnetic pole of the earth. My explanation is somewhat wordy, but hopefully it answers question #1. I think for question #2, the answer is the same as question #1.

3. Sep 10, 2017

Hawksteinman

A magnet's North Pole would point North. This is because the magnetic field lines go out from the North Pole of the magnet and into the North Pole of the Earth. Therefore Earth's North Pole is actually a South Pole.

And as for the other planets' North and south poles, some have them the right way round and some don't.

Source: Brian Cox's Wonders of the Solar System (book) and a link here: https://en.m.wikipedia.org/wiki/Poles_of_astronomical_bodies?wprov=sfti1

4. Sep 10, 2017

davenn

Charles's explanation is only part of it
He hasn't taken into account that the magnetic poles periodically flip.

in times gone bye, magnetic north and geographic north poles were both at the "top end" and times before that it was opposite as it is now so there is no point renaming it ... it is scientifically accurate as it stands

Some time in the future it will flip again and once again the magnetic north pole will be up the top end and all the red
ends of our compass needles (that we have labelled as north seeking) will be incorrect

well it has to be, as you already established in your first post that the geo. south pole was the magnetic north pole

and some don't have magnetic fields at all

Dave

Last edited: Sep 10, 2017
5. Sep 10, 2017

Staff Emeritus
1) The Earth's North Magnetic Pole is (today) a Magnetic South Pole.

2) This is well known. Maybe you didn't know this, but nevertheless it is well known.

6. Sep 10, 2017

Hawksteinman

So 1) is because the magnetic field flips?

And 2) is for the same reason?

7. Sep 10, 2017

8. Sep 10, 2017

davenn

as I said earlier .... yes

9. Sep 10, 2017

This question seems to be answered by the "link" of post #7. The northern hemisphere was not a magnetic north pole any time in recorded history according to this article.

10. Sep 10, 2017

stefan r

The history of magnetic pole flips are recorded by rocks cooling on the sea floor.

11. Sep 11, 2017

davenn

no one said it was

yes, and that's where it was first discovered and recognised for what it was
and if you hadn't mentioned it, I was going to

I was first made aware of it during a1980's TV series "Planet Earth"

Drummond Matthews and Frederick Vine at Cambridge University during ~ 1962 - 1965 unlocked the secret
of the magnetic stripes in the rocks on either side of the oceanic spreading ridges

WOW ... that's a life time ago when I was watching that

cheers
Dave

12. Sep 14, 2017

Stavros Kiri

I assume that North and South were determined long before magnetism was discovered.