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I How to find true north not magnetic north?

  1. Jul 7, 2018 #51
    Yes the goal is to find solar noon but at the time of this post I figure the easy way to do that is check the angle from the magnet noon shadow. But now i know magnet noon changes every day so my original idea will not work. Using noaa and GPS reading I am not sure the answer is correct. Solar noon will not be the same every day either. Earth orbits sun every 365 days, 5 hrs, 48 min, 46 seconds. On leap year longest day of the year is June 21, the next year June 21, the next year June 22, the next year June 22, after leap year June 21 again. Every year earths orbit is off 1/4 day plus 1 min 14 seconds. We make up the 1/4 day with leap year every 4th year but we never make up the 1 min 14 seconds. In about 54 years earth orbit is off 1 hour and about 1296 years earth orbit is off 1 day. Now I see only way to know for sure where solar noon is every day do the math every day I can not find solar noon with the clock or magnetic noon. Online information says, people navigated earth for 100s of years by using the North star and other stars. Funny thing 1977 scientist published a paper that said, The north star is the only star in the northern sky. Scientists thought they had learned something but the Bible written 2000 years earlier says, The north star is the only star in the northern sky. LOL I don't know how to find solar noon with the north star I can't even see the north star during the day. Online says, find solar midnight to know where solar noon is. This was all very educational I never knew solar noon moves every day.

    https://scontent-atl3-1.xx.fbcdn.ne...=f590686a6ee74ac7262ebb06b786eb04&oe=5BA149DE
     
  2. Jul 7, 2018 #52

    anorlunda

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    Whoa. You're going off the deep end of complexity. What are you trying to accomplish? I thought it was aligning a sundial.
     
  3. Jul 7, 2018 #53

    Tom.G

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    I just ran the experiment. An insanely strong magnet from a disc drive head positioner versus a medium size paper clip magnetized from it.

    Suspended the magnet with about 3 feet of sewing thread and got it settled pointing North. Then moved it near the refrigerator and it rotated about 45° when a foot away. The paper clip had to approach to about two inches before rotating the same amount.

    Conjecture: the field from a compass pointer should be about the same strength as the Earth magnetic field for minimum interference from nearby ferrous objects.

    Cheers,
    Tom
     
  4. Jul 8, 2018 #54

    Dale

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    And you believe that expensive compasses are made from insanely strong magnets?
     
  5. Jul 8, 2018 #55

    Tom.G

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    Not necessarily. Just pointing out that a much maligned condition as stated by the OP can, in fact, occur. I presume that at least some compass manufactures would be aware of the condition, even if other folks are not.
    Consider those "Stud Finders" you can by in the loacal hardware store. Some are just a suspended magnet that point to the nails holding the wallboard to the studs. Same idea, on a smaller scale and range.
     
  6. Jul 9, 2018 #56

    Vanadium 50

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    Compasses are not stud finders.
    Compasses are not made with superstrong magnets that can magnetize the surrounding objects.
    "Much maligned" is for a reason.
     
  7. Jul 9, 2018 #57

    Dale

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    But not with compasses, regardless of the price of the compass. The condition stated by the OP does not occur. The condition was not regarding magnets of varying strengths, but compasses of varying price.
     
    Last edited: Jul 9, 2018
  8. Jul 9, 2018 #58

    sophiecentaur

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    If you are sailing, the compass heading can be at least as useful as the COG (Course O~ver Ground), which is what the GPS tells you (after a finite delay).
     
  9. Jul 9, 2018 #59

    anorlunda

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    I would say that we are getting off-topic except that the topic of this whole thread is very unclear.

    Not always true. Consider the limiting case of a vessel adrift in a current. GPS tells you COG. Compass heading may be anything 001-360 degrees. The compass tells which direction the bow points, but that is irrelevant to motion in that case.

    When fresh water sailors first encounter salt water tidal currents, they can be seen to mistakenly believe that motion of their boat is in the direction the bow is pointing.
     
  10. Jul 9, 2018 #60

    sophiecentaur

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    I used the word “can” and seeing the effect of leeway and tide is very useful at times. Bearing, Heading and COG all have their place. The good old magnetic compass should be the last thing you chuck over the side (except perhaps for the Aeropress coffee maker).
     
  11. Jul 9, 2018 #61
    Maybe I should make it clear that I have 4 compasses. 3 are low cost boy scout compasses. All 3 boy scout compasses appear to be identical and made by the same company except that 1 is green color the other 2 are black. I paid $2, $3 & $5 for the boy scout compasses so I am calling these cheap or low cost compasses. Needle sticks on the $2 green compass. The dial sticks on the $3 black compass. The $5 compass works best of the 3. I also have a more expensive compass that cost $20 but maybe the price should not be considered as making it be a better compass than the $5 compass. The $20 needle moves very smooth and the dial rotates very nice much better than the $5 compass. The more expensive compass has a stronger magnet field on the needle that is why it is more sensitive to metal objects near by. The $20 compass is hard to use to adjust my TV antenna because I have to stand too far away from the TV antenna to make adjustments. There you have it the details of my 4 compasses. I consider the $2 & $3 compass to be basically worthless. If I am lost in the wilderness I would like to have the $20 compass as long as I am not lost near a large iron ore deposit in the earth.
     
  12. Jul 10, 2018 #62

    Baluncore

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    Do not rely on any magnetic compass, at any price. There is too much variation, local field or magnetic storm.

    You read your Lat/Long with GPS earlier. Now go to a point as far away that you can see from the first site. Read the GPS there. Go back and check the first point. You now have two points on the WGS84 ellipsoid. Use navigation software to find the bearing from the first point to the second, remote point. Offset that bearing from that survey line to find the N-S meridian.
     
  13. Jul 10, 2018 #63

    Baluncore

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    But since I'm South of the equator, it gives me North.
    That will only give an approximation of the North-South meridian line. It depends on your longitude in the time zone and a seasonal correction using the Analemma.
    That sundial correction oscillates between –14min 15sec and +16min 25sec.
    See; https://en.wikipedia.org/wiki/Analemma
    https://en.wikipedia.org/wiki/Equation_of_time
     
  14. Jul 10, 2018 #64

    Dale

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    I doubt this is correct. I suspect that most of the difference in sensitivity is due to the better bearings
     
  15. Jul 10, 2018 #65

    anorlunda

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    @gary350 , please answer the question. What are you trying to accomplish?
     
  16. Jul 10, 2018 #66
    That is true the $20 does have a better needle movement. If I go out into the center of the front yard where there is no fence and no metal with 2 compasses the needle point at each other. If I put both compasses on the ground and move them apart soon earth magnetic field becomes stronger than the other compass needle and they both stop pointing at each other and point at magnetic north.
     
  17. Jul 10, 2018 #67

    Baluncore

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    When close, they should align, but with the North pole of one pointing to the South pole of the other.
    When far apart, they do not both point to magnetic North, they will always influence each other.

    There is no point buying a magnetic compass if you want to know true North.

    QUESTION; Why do you need to know true North?
     
  18. Jul 10, 2018 #68

    anorlunda

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    I think this thread has run its course.

    Thread closed.
     
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