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Author Topic: Why don't our compasses point at the sun?  (Read 1120 times)

Offline Europan Ocean

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Why don't our compasses point at the sun?
« on: 04/07/2013 13:20:12 »
Why don't our compasses point at the sun? Whether from Sydney or the north pole?


 

Offline Pmb

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Re: Why don't our compasses point at the sun?
« Reply #1 on: 04/07/2013 15:18:36 »
Quote from: Europan Ocean
Why don't our compasses point at the sun? Whether from Sydney or the north pole?
For two reasons (1) the compass needle always points in a direction parallel to the field, not to the direction of the source of the field and (2) the strength of the magnetic field due to the sun at the earth's location is so small as to be insignificant and thus can be ignored when compared to the strength of the earth's magnetic field.
 

Offline CliffordK

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Re: Why don't our compasses point at the sun?
« Reply #2 on: 04/07/2013 16:29:12 »
The strength of a magnetic field decreases with the square of the distance.  So, at about 150,000,000 km from the sun, the field strength would be quite small, and largely overwhelmed by the Earth's magnetic field.

As Pete mentions, the magnetic field would have both a N & S, component so your magnet could not orient towards the sun, but rather parallel to the sun's field.

HOWEVER,
There are several magnetic solar observatories right here on Earth, including the Wilcox Solar Observatory, and the Mt. Wilson Solar Observatory

So, it is possible to measure the sun's magnetic field in high resolution her on Earth. 

Anybody have a good simple explanation of how they work?
 

Offline Pmb

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Re: Why don't our compasses point at the sun?
« Reply #3 on: 04/07/2013 17:04:30 »
Quote from: CliffordK
The strength of a magnetic field decreases with the square of the distance.
The sun has the magnetic field of a magnetic dipole, just like earth does. The magnetic field of a dipole decreases as the cube of the distance, not the square.

The value of the magnetic dipole moment of the earth that is listed in Halliday and Resnik is 8.0x1022J/T.

The value of the magnetic dipole moment of the sun listed here
http://icrc2001.uni-wuppertal.de/ICRC2001/papers/icc1530_p.pdf is 6.87x1032G*cm3

I don't know what the conversion factor is or even what that "G" means in that value. Does anybody else know?
 

Offline yor_on

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Re: Why don't our compasses point at the sun?
« Reply #4 on: 04/07/2013 17:34:14 »
from The Cambridge Guide to the Solar System. By Kenneth R. Lang.

(Why can't I attach a photo any more?) Eh, ok, I apparently could :)
 

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Re: Why don't our compasses point at the sun?
« Reply #4 on: 04/07/2013 17:34:14 »

 

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