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Thread: Magnetism In Space

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    Magnetism In Space

    1. Which way does the North pole of a magnetic compass point when in deep space, that is outside of the Earths influence? How about when on the Moon? How about when near Mars? Do we do any magnetic experiments in space?

    2. Does light exert a magnomotive force on electrons or protons?
    3. Doe it affect protons or electrons more?
    4. What are unusual space phenomenon, such as a match buring in a circle of flame, plants not growing in space, change in height of a person, etc? Any links?
    5. Do other planets orbit other stars in an ellipsis? Is there ellipsis parallel with our solar system?
    6. Are there more protons or electrons in light from the sun?
    7. Are there more protons or electrons coming from Polaris?

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    Re: Magnetism In Space

    Welcome to the board.

    Quote Originally Posted by TheWatcher
    1. Which way does the North pole of a magnetic compass point when in deep space, that is outside of the Earths influence? How about when on the Moon? How about when near Mars? Do we do any magnetic experiments in space?
    A compass would inevitably point to the strongest north pole. In interplanetary space, that would be the Solar north pole, wherever that is. It's all to do with the net field. At any given point, the magnetic fields of Earth, Mars, Sol, everything, all sum to produce a net magnetic field. The north seeking pole of a compass would point in the direction of the net field lines. On Earth, the geomagnetic field is so strong compared to the others, that the others are not that significant, so the compass points in the directions of the field lines which are heading towards the north geographic pole.

    Quote Originally Posted by TheWatcher
    2. Does light exert a magnomotive force on electrons or protons?
    Photons of light can transfer their momentum to electrons or protons, but that's not to do with any magnetic fields. Light has no net magnetic polarity.

    Quote Originally Posted by TheWatcher
    3. Doe it affect protons or electrons more?
    See above.

    Quote Originally Posted by TheWatcher
    4. What are unusual space phenomenon, such as a match buring in a circle of flame, plants not growing in space, change in height of a person, etc? Any links?
    In zero-g, there is no convection. The shape of a flame, being a point upwards is due to convection, where the hot air in the flame rising. Without convection, there is no movement of air as a result of temperature difference so the hot air sits around the flame. This can be useful because the air sitting around the flame would before long become carbon dioxide and may end up suffocating the flame, putting out any fire, although that's not a foolproof prevention.

    IIRC, plants have these chemicals called tropisms that cause them to grow different parts in different directions. The shoot is sensitive to light and will grow in the direction of light so the leaves can photosynthesise. The roots are sensitive to gravity and will grow downwards to find water. I can't remember the terms for that type of behaviour. In zero-g, the tropisms would have no gravity to detect and so one might think they'd have problems growing their roots. However, I believe many plants have been successfully grown.

    Quote Originally Posted by TheWatcher
    5. Do other planets orbit other stars in an ellipsis? Is there ellipsis parallel with our solar system?
    That would be an ellipse. I don't know for sure, but I'd think it is highly likely that the orbits of detected extrasolar planets are slightly eccentric. It's tough to be sure because planets have only been detected indirectly by detecting wobbles of stars. One bit of uncertainty is inclination. We don't know if the wobble is due to a relatively small planet in an orbital plane in which our line of sight lies or the wobble is due to a honkin' great big planet in a highly inclined orbit. There is no reason to think that the orbital planes of other planets are parallel to the ecliptic.

    Quote Originally Posted by TheWatcher
    6. Are there more protons or electrons in light from the sun?
    Light from Sol doesn't contain protons or electrons, it contains photons. The solar wind contains protons and electrons though. Someone else will probably know the answer to that.

    Quote Originally Posted by TheWatcher
    7. Are there more protons or electrons coming from Polaris?
    Polaris is over 400ly away. We don't know the composition of its solar wind.

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    Re: Magnetism In Space

    Quote Originally Posted by Glom
    A compass would inevitably point to the strongest north pole. In interplanetary space, that would be the Solar north pole, wherever that is. It's all to do with the net field. At any given point, the magnetic fields of Earth, Mars, Sol, everything, all sum to produce a net magnetic field. The north seeking pole of a compass would point in the direction of the net field lines. On Earth, the geomagnetic field is so strong compared to the others, that the others are not that significant, so the compass points in the directions of the field lines which are heading towards the north geographic pole.
    Time for a little Bad Physics here.

    If you were to place two bar magnets end to end, you would note that the north pole of one magnet is attracted to the south pole of the other magnet. From this you could say that a north pole of a magnet is a "south-seeking pole." Now, take one of the bar magnets and hang it from a string - but tie the string in such a way that it forms two loops from a central point, so that you are able to hold the magnet parallel to the ground. The magnet will align itself with the magnetic field. You will see that the north pole of the magnet is facing North!

    Explanation: what we call the North pole of the Earth is really a South pole!

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    That's the thing. The North pole of a magnet is the North-Seeking pole. It seeks the north pole of this planet. That's how it's defined. By that definition, the north magnetic pole is technically a south pole.

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    nebularain
    Explanation: what we call the North pole of the Earth is really a South pole!
    No it is not realy the south pole because earth is the "gage" of what we difine this by. Similarly in engineering clockwise is defined by the objects serface looking outwards and then turning to the right, witch mean when you design a clock it every component is desinged to travel ant-clockwise. So realy clocks are move anti-clockwise but thats the gage so there special in a sense

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    North Pole

    Thank you for your replies, however, I know that a compass will point towards the strongest North Pole whether that be a single pole or a combination of poles.

    Now the Moon has a North Pole. At what point does the compass in space begin to swing towards the North Pole of the Moon rather than towards our north pole? How about the North Pole of Mars? We need a magnetic map of space twixt here and Mars or where ever we are going?

    Second, about the match burning witha circular flame in a space ship. Well, you said something about convection currents causing a flame to be pointed up, well certainly on a space craft there is air and convection currents and yet the flame burns in a sphere. Certainly if convection is causing the pointed flame, then it should also happen in a space craft.

    And yes, the North Pole of the Earth is really a South Pole according to our conventions.

    Does anyone know of any other space physics anamolies such as the ones I"ve mentioned?

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    There is air current's on a space ship but not convection. Convection is caused by warmer air rising and cooler air sinking. In a freefall environment that doesn't happen, and since there are probably not any strong currents on a spacecraft you'll get a mildy distorted sphere.

    And we really don't need a magnetic map of space because there's no point in having a compass. Magnetic fields are constantly changing as the planets orbit and mapping them would be a nightmare.

    The north pole isn't really a south pole, the north seeking end of a compass is just that, a north seeking end. Our magnetic fields are named in relation to the North and South poles of the Earth.

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    Re: North Pole

    Quote Originally Posted by TheWatcher
    Now the Moon has a North Pole.
    No it doesn't. The magnetic fields of planets and stars come from spinning cores. The Moon has cooled off and no longer has a spinning core so it does not have a magnetic field.
    We need a magnetic map of space twixt here and Mars or where ever we are going?
    No, I presume one uses calculations of forward momemtum and gravity's influence to direct one's spacecraft.
    Second, about the match burning witha circular flame in a space ship. Well, you said something about convection currents causing a flame to be pointed up, well certainly on a space craft there is air and convection currents and yet the flame burns in a sphere. Certainly if convection is causing the pointed flame, then it should also happen in a space craft.
    Not necessarily. I don't know what a flame looks like away from the Earth's gravity, but a convection current needs gravity to see heated gas rise. Otherwise you get a pressure gradient that probably causes the heated gas to spread out in all directions equally, or at least with equal action against the existing pressure of the non-heated gas.

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    Re: Magnetism In Space

    Quote Originally Posted by Glom
    Polaris is over 400ly away. We don't know the composition of its solar wind.
    Spectral analysis wouldn't tell us? (I am asking not suggesting it would.)

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    Re: Magnetism In Space

    Quote Originally Posted by beskeptical
    Quote Originally Posted by Glom
    Polaris is over 400ly away. We don't know the composition of its solar wind.
    Spectral analysis wouldn't tell us? (I am asking not suggesting it would.)
    That would tell you what the star is made of, but not necessarily what elemets make up it's solar wind, or in what ratios

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    Additional note:

    Colder gas is heavier than hotter gas of the same composition. Colder gas has less active molecules so they hit eachother less and end up more densely aggregated. Hotter gas molecules have more energy and hit eachother more often so they end up farther apart and therefore less dense. So...hotter gas is less dense, colder gas more dense. But..... the direction of the two gases would be random except for the influence of gravity.

    Without gravity, mixing two gasses of the same composition but two temperatures in a limited space gives you diffusion of the two until an equilibrium is reached. But without gravity, the diffusion would be across a pressure gradient, not a gravity defined pressure gradient.

    PS. I have to type fast to post this before the other folks who know this stuff do a better job. :wink:

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    Quote Originally Posted by wedgebert
    The north pole isn't really a south pole, the north seeking end of a compass is just that, a north seeking end. Our magnetic fields are named in relation to the North and South poles of the Earth.
    Then why does the north pole of a bar magnet face North, as I mentioned above? (We did this experiment in my physics class, so I know it happens.)

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    Because the "North Pole" of a bar magnet is really a "North Seeking Pole".

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    There's that silly language stuff getting in the way of communication again.

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    A few things that haven't been fully answered on this thread:

    Do we do any magnetic experiments in space?
    Magnetometers that measure the magnitude and direction of the local, cumulative magnetic field are standard equipment on nearly all scientific spacecraft.

    Now the Moon has a North Pole...How about the North Pole of Mars?
    The Moon and Mars have no intrinsic, global magnetic fields, but they do have magnetized surface regions that act as "permanent magnets". Studying the surface magnetism of these bodies helps in our over-all understanding of them. Of all the solid bodies in the Solar System, only the Earth, Mercury and Ganymede (a moon of Jupiter) are known to have intrinsic global magnetic fields. The magnetic field of the Sun is "frozen to" the solar wind and is carried along with it. The resulting Interplanetary Magnetic Field (IMF) is very dynamic and changes both its magnetude and direction frequently.

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    Quote Originally Posted by Glom
    IIRC, plants have these chemicals called tropisms that cause them to grow different parts in different directions. The shoot is sensitive to light and will grow in the direction of light so the leaves can photosynthesise. The roots are sensitive to gravity and will grow downwards to find water. I can't remember the terms for that type of behaviour. In zero-g, the tropisms would have no gravity to detect and so one might think they'd have problems growing their roots. However, I believe many plants have been successfully grown.
    This is a pleasantly picky thread - and I can't let this go since my background is in life science. Although you are very roughly right about plant development, Glom, a 'tropism' is not a chemical. It actually means, very simply, a tendency to move (or grow) in one direction (remember that astronomers often use the word 'isotropic' - literally same direction, in a different context). So 'geotropism' is a tendency to grow downwards into the Earth - rootlike behaviour. 'Phototropism' - grows toward the light. Hydrotropism (obvious), etc etc.

    There are, of course, chemicals involved, but the metabolic processes are sometimes simple, sometimes not, and sometimes not well understood. Having said that, if you take a 'standard' green plant as the sum of its tropisms, it won't actually have much of a problem in microgravity (though it may end up looking a bit funny). The leaves and shoots are phototropic - they'll reach out towards an available light source, just as your houseplants will reach out for the window.

    Root development is not actually dependent on gravity - roots look for nutrients and water (hydrotropism) and can be quite clever about figuring out density gradients in these respects - plus they frequently exhibit negative phototropism - they often just don't like light sources. I've gone on a bit long - but to put it simply, unlike us upright bipeds, plants just don't have a discernable gravitational detector. Light, water and nutrients are top of their fave rave list.

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    Re: Magnetism In Space

    Quote Originally Posted by wedgebert
    [Spectral analysis] would tell you what [Polaris] is made of, but not necessarily what elemets make up it's solar wind, or in what ratios
    Some stars have emission lines in their spectra, indicating that they're surrounded by a lot of hot gas. An ordinary stellar wind is too tenuous to produce any appreciable emission lines, though.

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    Small (sort of correction thing) to my early post. The older term for plant-light growth tendencies is in fact 'phototrophism'. I've just been checking and this seems to be now interchangeable with 'phototropism'.

    In the context of plants, one can see why, because trophism is a growth tendency (cf 'hypertrophy'), whereas a tropism is an attraction towards something, a leaning... But how would you tell the difference with a plant?

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    Quote Originally Posted by Beaver
    No it [the North pole of the Earth] is not realy the south pole
    It really is a south magnetic pole.
    Quote Originally Posted by wedgebert
    The north pole isn't really a south pole
    Oh yes, the North Pole is really a south magnetic pole.

    I discussed it in an earlier thread as well.

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    Part of the trouble is that there are two definitions for "north" and "south".

    One refers to magnetics. The Earth's northernmost magnetic pole is a south pole.

    The other refers to rotation and is purely arbitrary. If you have a body which is rotating in a normal fashion (and that definition is arbitrary too, but for planets its defined as the Sun rising in the east), and you are looking at it from its equator such that a point on the equator appears to travel from left to right, then the part of the planet facing "up" from your perspective will be north.

    So our north magnetic pole is, magnetically speaking, a south pole.

    And our north rotational pole is a north pole.

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    Oh, good catch, calliarcale! And of course planets with no global magnetic field still have, by convention, a north and south pole as defined by their axis of rotation as you describe. The Earth has a geomagnetic north pole and a geographic north pole, and they're in different locations. The Moon has a selenographic north pole but no selenomagnetic north pole 'cos it has no global magnetic field, right?

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    Quote Originally Posted by calliarcale
    Part of the trouble is that there are two definitions for "north" and "south".

    One refers to magnetics. The Earth's northernmost magnetic pole is a south pole.

    The other refers to rotation and is purely arbitrary. If you have a body which is rotating in a normal fashion (and that definition is arbitrary too, but for planets its defined as the Sun rising in the east), and you are looking at it from its equator such that a point on the equator appears to travel from left to right, then the part of the planet facing "up" from your perspective will be north.

    So our north magnetic pole is, magnetically speaking, a south pole.


    And our north rotational pole is a north pole.

    So when they switch - which is which?

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    Jay Leno had a 'Debate by two of the Jay Walk Allstars' the other night. One of the two said she didn't believe there was a North Pole because that was just part of the Santa Claus myth.

    When Jay brought out a world globe, he went to show her the North Pole but it wasn't on the globe. I laughed some more because I don't think he realized he was confusing the North Magnetic Pole with the northern axis of rotation.

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    Back to what a compass would read outside of our earth's magnetic field. If I'm not mistaken, it would point toward the pole of Jupiter.

    Jupiter has the strongest magnetic field in the solar system, even stronger than the sun. So if some alien race were looking for magnetic fields in our solar system from far away, the magnetic field they would measure would be due more to a planet than to the star.

    -Cpt Steiny

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    Quote Originally Posted by CptSteiny
    Back to what a compass would read outside of our earth's magnetic field. If I'm not mistaken, it would point toward the pole of Jupiter.
    You've got a logical inconsistency. If there's a place that's 'outside of our earth's magnetic field' (which to all intents and purposes there is), then there's a place that's outside Jupiter's magnetic field, no matter how big that may be. So, no - you have to specify a more exact location for your compass.

    Magnetometers (rather more sophisticated instruments than compasses) are flown on spacecraft all the time. In the space between planets, the results are largely dominated by solar wind interactions.

    Here is a list of publications by the magnetometer experimenters working with Ulysses: http://www.sp.ph.ic.ac.uk/Ulysses/Pub/pub2000.html (that's the solar polar mission). If you flick through quickly, you will see that the titles from the investigators include entries like:

    The latitudinal distribution of solar wind magnetic holes

    There is one such study on Jupiter, but Ulysses was only able to study that field because it made a close fly-by on its first solar orbit.

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    But wouldn't the compass have to be close enough to Jupiter to distinguish the North and South magnetic poles? I mean, if a compass needle is designed to be attracted to magnetic north, an Jupiter is so from us that to point the compass at Jupiter, the compass would be facing both Jupiter's north and south magnetic poles, wouldn't the poles kind-of cancel each other out as far as the compass is concerned - or something like that?

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    Yes, Grand Vizier, I wrote my response too quickly and I do understand that. But, the main point I wanted to get across was that from outside our solar system, the magnetic field we would detect would be that of Jupiter mostly, and very little of the sun's.

    To nebularain.....
    Any compass points along the magnetic field lines in whatever system it may be in. Here is a link to a drawing of magnetic field lines that I'm thinking about http://www.mines.edu/fs_home/tboyd/G...ES/fieldl.html.

    The magnetic polar axis is horizonal in this model so in our jupiter case we would be somewhere upward or downward looking at Jupiter. Our compass would still point downward if we were directly in the "equatorial" plane of Jupiter's magnetic polar axis. But if we deviate from this plane, our compass changes it's orientation quite a bit. Think of a compass as a device that points along magnetic field lines.

    So if we stayed on the "equatorial" plane of Jupiter's magnetic pole orientation our compass would always point in the same direction.

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    Quote Originally Posted by CptSteiny
    Yes, Grand Vizier, I wrote my response too quickly and I do understand that. But, the main point I wanted to get across was that from outside our solar system, the magnetic field we would detect would be that of Jupiter mostly, and very little of the sun's.
    Well, I doubt this . The fact is that there are magnetometers on the Voyager spacecraft and they are busy now studying the solar wind way beyond Neptune. (It's something of a surprise how far out this extends - it's hoped soon that they will reach the heliopause, where there will be a 'shock region' as the wind meets interstellar matter).

    The point is that just as magnetometer readings are dominated by the solar wind, so would a compass be. In other words it would swing around in a way determined (at a long distance) by events on the Sun that happened hours before.

    Actually I don't think anyone knows how a compass or magnetometer would behave beyond the heliopause - but that's one reason that people are looking forward to the Voyagers going there. Maybe the galactic magnetic field would show up - but very very weakly - maybe not enough to move a compass.

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    Jupiter has the strongest magnetic field in the solar system, even stronger than the sun. So if some alien race were looking for magnetic fields in our solar system from far away, the magnetic field they would measure would be due more to a planet than to the star.
    Jupiter does indeed have a strong magnetic moment (about 20,000 times the Earth's) and the Sun's is highly variable, however, this does not mean that interplanetary space is dominated by Jupiter's magnetic field. If there was no solar wind this might be true, but the solar wind is a plasma (charged particles) which causes the magnetic field lines to "blow back" and remain confined to a planetary magnetosphere. If you could see Jupiter's magnetosphere with your eyes, it would appear larger from the Earth than the full Moon (about 80 times the planet's own radius), but that is still only a fraction of the volume of the Solar System. Now, being blown back, magnetospheres have long tails pointing away from the solar wind direction. In this dimension Jupiter's magnetosphere reaches beyond Saturn's orbit, but becomes increasingly narrow and weak.

    One more thing, I don't know of any way to "remote sense" a magnetic field, so if aliens were looking from far away they would measure their own field, not ours. :-?

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    Quote Originally Posted by waynek

    [...]

    One more thing, I don't know of any way to "remote sense" a magnetic field, so if aliens were looking from far away they would measure their own field, not ours. :-?
    Good post - just adding to it.

    Re: remote sensing - totally true you can't sense the magnetic field directly as you can do with EM radiation, but you can infer its presence and effects by the behaviour of charged particles accelerated by it, by radio emissions etc (which is how we knew Jupiter had a magnetosphere before going there - same goes for our Galaxy and other galaxies).

    But, with regard to CptSteiny's point, I thought about this later and, with respect, Steiny, I think you're equating magnetic fields with gravity fields. They're not the same thing. Apart from the fact that electromagnetism (as a force) falls off with the cube of the distance and gravity with the square, magnetic fields are bipolar (there are theoretical ideas of magnetic monopoles, but none have been found), so...

    If you want to look at gravity as an attractive field emanating from any piece of matter and extending to infinity (one way of looking at it, I guess), then your compass concept holds (if you have a gravitational compass ) but then gravity is monopolar. On the other hand, a bipolar magnetic field loops back on itself and can be compressed/confined by interaction with other fields and charged particle flows, as waynek points out. We have no way of confining or shielding gravity - would be pretty cool if we did.

    Magnetic fields are easily blocked out/pushed back naturally and artificially. So the only real answer to your compass question is 'the north pole of the most intense field available in your vicinity at the time you are doing the measurement'. Not terribly satisfying, true...

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