# The Naked Scientists Forum

### Author Topic: How far into space would you need to travel for a magnetic compass not to work?  (Read 508 times)

#### thedoc

• Sr. Member
• Posts: 511
• Thanked: 12 times
##### How far into space would you need to travel for a magnetic compass not to work?
« on: 05/10/2016 11:53:01 »
If magnets rely on north south poles, how far into space would you need to travel for them not to work??
What do you think?
« Last Edit: 14/10/2016 22:02:34 by chris »

#### Janus

• Full Member
• Posts: 76
• Thanked: 14 times
##### Re: If magnets rely on north south poles, how far into space would you need to travel for them not t
« Reply #1 on: 11/10/2016 21:23:16 »
Why do you think magnets would quit working in space? It's not as if the magnet's magnetism is dependent of on the Earth's magnetic field.

#### alancalverd

• Global Moderator
• Neilep Level Member
• Posts: 4704
• Thanked: 153 times
• life is too short to drink instant coffee
##### Re: If magnets rely on north south poles, how far into space would you need to travel for them not t
« Reply #2 on: 11/10/2016 21:25:18 »
Magnets have north and south poles, they don't "rely" on them.

#### evan_au

• Neilep Level Member
• Posts: 4109
• Thanked: 245 times
##### Re: If magnets rely on north south poles, how far into space would you need to travel for them not t
« Reply #3 on: 12/10/2016 08:50:49 »
If you had two bar magnets floating in space, they would interact with each other - a "North" tries to get close to a "South".

The Earth is a bar magnet floating in space. So another bar magnet floating in space will interact with the Earth.

But something strange goes on here: the "North" of the bar magnet tries to get close to the North pole of the Earth (that's what gave the North pole of the bar magnet it's name). So the North pole of the Earth is actually a "South" pole!

In theory, the range of a magnetic field is infinite, but in practice, the force of a bar magnet declines much more rapidly than inverse-square law effects like electrostatic charges, gravity or light intensity. This is because the North and South poles are near each other, and from a viewpoint far away, almost cancel each other out.

This makes it much easier to detect Jupiter with a telescope than with a compass, despite Jupiter's powerful magnetic field.

#### Otto Grunf

• First timers
• Posts: 1
##### Re: If magnets rely on north south poles, how far into space would you need to travel for them not t
« Reply #4 on: 12/10/2016 09:10:25 »
l believe what the Doc meant was ,, how far into space does one have to go before COMPAS stops functioning?" , not the " magnet".
If this the case, I'd add " ... and at what distance will some other source of magnetic field prevail? And which one?"

#### Nilak

• Sr. Member
• Posts: 180
• Thanked: 8 times
##### Re: If magnets rely on north south poles, how far into space would you need to travel for them not t
« Reply #5 on: 13/10/2016 09:12:40 »
As soon as you create a magnet ( ex. Power on an electromagnet) the magnetic field propagates and travels forever at speed c. In my opinion, It is like pulling an infinitely long elastic string. When you turn off the magnet it is like releasing the string with a fixed speed less than c. Then it starts to oscillate. In reality is much more complicated because the N ans S poles create loops and I find difficult to explain propagation. But c is the speed limit for sure. And the field will always be present, no matter how far you go.

#### evan_au

• Neilep Level Member
• Posts: 4109
• Thanked: 245 times
##### Re: If magnets rely on north south poles, how far into space would you need to travel for them not t
« Reply #6 on: 13/10/2016 11:17:09 »
Quote from: Otto Grunf
how far into space does one have to go before COMPAS stops functioning
This website provides access to magnetic field data from various space probes.
http://omniweb.gsfc.nasa.gov/coho/

For example, the Voyager 1 spacecraft has magnetic field data from 2 days after its launch in September 1977.

Looking at the Tangential field measurements (which I presume is what we measure with a compass at the equator), the polarity oscillates in the first week of data, so the Earth's magnetic field is already lost.

I assume that the magnetic field polarity being measured here would be the magnetic field carried by the Solar wind.

#### Janus

• Full Member
• Posts: 76
• Thanked: 14 times
##### Re: If magnets rely on north south poles, how far into space would you need to travel for them not t
« Reply #7 on: 13/10/2016 15:34:05 »
l believe what the Doc meant was ,, how far into space does one have to go before COMPAS stops functioning?" , not the " magnet".
If this the case, I'd add " ... and at what distance will some other source of magnetic field prevail? And which one?"

In this case, we would be talking about the boundary of the magnetosphere.  This is neither really "sphere" nor does it end at a set distance from the Earth. It's size and shape depends on the Solar wind.  The boundary is closer to the Earth on the Sun-ward side than it is on the opposite side by about a factor of 6 (~10 Earth radii to ~60 Earth radii.)  Variations in the Solar wind cause the boundary to vary also.

#### The Naked Scientists Forum

##### Re: If magnets rely on north south poles, how far into space would you need to travel for them not t
« Reply #7 on: 13/10/2016 15:34:05 »