planet's magnetic field

[gcks]

Where does all this magnetic field between north and south poles come from?
Well, I realise that it has something to do with iron and spin of the planet...
does moon or venus have a magfnetic field?(low spin)
in where does this involve between planets in the solar system(as a whole)?(did that make any sense?)

[Dingo1]

The magnetic field is the result of the spin of our iron/nickle core.  This spin is like a giant dynamo, which generates an electromagnetis field around the planet.

[gcks]

What about Venus or Moon ? What about other natural sattelites?
Is the spin of Earth constant (and ,thus,the magnetic field) during its rotation around the sun? Is it constant throughout the time ( the centruries)?

[remcook]

the Earth magnetic field is far from constant. Every once in a while it even changes north-south!

[gcks]

it even changes north-south

How ! Is this possible? That would mean that earth should spin clockwise ! which is not possible according to what I have learnt so far...

[gcks]

And besides that...
The most convienient answer should be : "constant"
Since earth revolves around its axis once every 24 hours, no less nor more(I hope so..),
its spin should be constant and so should its magnetic field
or are there any other factors that affect the field besides spin?

[remcook]

the spinning of the core is not directly related to the spinning of Earth as an entire planet. The core spins relative to the rest.

Mars does not have a magnetic field for instance (or hardly any). And neither does the moon. But mercury has a magnetic field (http://messenger.jhuapl.edu/why_mercury/index.html#4)

some links:

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magearth.html
http://news.nationalgeographic.com/news/2004/09/0927_040927_field_flip.html

[gcks]

thank you , remcook. ..very enlightening.
So, does sun have a magnetic field? ( I have heard about sunspots and twisted magnetic fields in the photosphere that cause X-class rays- and storms that affect space weather in our solar system).

[gcks]

and what about gas giants ; Do they have magnetic field ?

[Orstio]

A magnetic field generation in the core of a planet does not necessarily indicate the "spinning" of the core.  There is enough hot liquid metal in the core of a planet that any movement of that liquid will generate a net magnetic field of some sort.  The magnetic field is most likely caused by more of a churning action of interacting boiling fluids than a single spinning action.  This would explain magnetic-reversal events, and also Saturn's magnetic field, whose poles actually rotate around the equator, rather than sit near the physical poles as ours does.

http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2004/06/29/MNG5H7DJIU1.DTL

The Sun has a huge magnetic field:

http://science.nasa.gov/ssl/pad/solar/the_key.htm

The Sun's magnetic poles switch every 11 years.

[Skyjim]

And I'm afraid you'll have to let go of the idea of the Earth's rotation rate being constant.  It is and always has been dynamic, with the gross change being a slow lengthening of the rotational period due to momentum transfer from Earth to Moon due to tidal effects. This results in a miniscule slowing of Earth's spin while the orbit of the Moon increases in radius - roughly 35-40mm a year if memory serves.

These changes are tiny on the scale of a human lifetime or ten, but over geological time they have resulted in significant lengthening of the Earth's day.

Jim

[Qazaq2003]

Gcks,
 Skyjim is correct in what he says about the Earth's rotation slowing down over time. In fact the rotation rates for all the planets in our solar system are slowing down, but the rate of rotational slowing is different for each planet. As for Earth's magnetic field reversing, that will have NO effect on the spinning of the Earth, the Earth ALWAYS spins in the same direction irregardless of the magnetic field polarity.  Q

[Dingo1]

Gcks, A good example for the efects of magnetic fields, look at the effects magnetic fields on the sun.  The magnetic fields get twisted and warped out of shape.  It is one of the major factors in sun-spots, these cool spots on the sun are generally the points where the magnetic field has been warped and breaches the surface of the sun.  Another visible effect are solar prominads  (flairs that loop).  The follow the magnetic field.
As for the flip-flopping of the polarity of the Earth's magnetic field, the exact mechanisim that triggers it about every 45,000 years (average) is unknown, and we are not sure of the over-all effects it will have.  Experiments have shown that electonics are effected  (sometimes), as well as other effects on things that rely on the magnetic fields.  Possible effects would be on natural navigation and migration patterns.  The magnetic poles have recently shifted by about 80 meters

[gcks]

Possible effects would be on natural navigation and migration patterns.

 
What do you mean?

[remcook]

birds.