Ture North, Magnetic North, Grid North ....

northernneil
northernneil Posts: 1,549
edited December 2010 in The bottom bracket
why when they start doing maps did they not line up the grid north with true north ?

and why dont they produce maps with grid lines that line up with magnetic north.. making it easier to take a compass bearing ?

Comments

  • balthazar
    balthazar Posts: 1,565
    edited December 2010
    Doesn't magnetic north wander about?

    Actually, reading these wiki pages about it, it seems that everything is mutable (it all wanders about).

    http://en.wikipedia.org/wiki/North_Magnetic_Pole

    http://en.wikipedia.org/wiki/North_Pole

    http://en.wikipedia.org/wiki/Polar_motion

    From that page: "It is desirable to tie the system of Earth coordinates (latitude, longitude, and elevations or orography) to fixed landforms. Of course, given plate tectonics and isostasy, there is no system in which all geographic features are fixed. Yet the International Earth Rotation and Reference Systems Service and the International Astronomical Union have defined a framework called the International Terrestrial Reference System."

    :shock:
  • Pross
    Pross Posts: 43,463
    Both Magnetic North (the point at which the earths magnetic pull is at 90 degrees) and True North (which is based on astrological readings) move. It is therefore impossible to match these two up or for grid north to match with either without maps having to be constantly reproduced but this would lead to confusion as grid co-ordinates would also be changing all the time. I suspect that when maps were first made grid north was aligned with either magnetic or true north.
  • bompington
    bompington Posts: 7,674
    Pross wrote:
    based on astrological readings
    :shock: :shock:
  • BarryBonds
    BarryBonds Posts: 344
    All you need to really know is "mag to grid, get rid"

    Simples
  • Chiggy
    Chiggy Posts: 261
    Also, the Earth's crustal plates are moving constantly. Europe is moving away from North America by about 1 inch per year. or is it the other way round, America from Europe?

    It's America from Europe because Greenwich is 0 longtitude.
  • term1te
    term1te Posts: 1,462
    True North I guess must start somewhere around Stoke or Nottingham?
    Magnetic North has to be Sheffield, with all that steel they used to make
    Grid North, would that centre on the Drax powerstation, or with polar shift is it now Sellafield?
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  • schweiz
    schweiz Posts: 1,644
    bompington wrote:
    Pross wrote:
    based on astrological readings
    :shock: :shock:

    :lol:

    I didn't know Mystic Meg worked for OS!
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  • bartimaeus
    bartimaeus Posts: 1,812
    Chiggy wrote:
    Europe is moving away from North America by about 1 inch per year. or is it the other way round, America from Europe?
    It's America from Europe because Greenwich is 0 longtitude.

    Here's a few years' worth of moving away...

    geoff-renner-rift-where-earth-is-splitting-at-plate-boundary-grotagja-lake-myvatn-region-iceland.jpg
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  • pneumatic
    pneumatic Posts: 1,989
    You forgot to mention the Frozen North :(

    Fast and Bulbous
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  • Ben6899
    Ben6899 Posts: 9,686
    It's grim up North.
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  • Squillinossett
    Squillinossett Posts: 1,678
    Ben6899 wrote:
    It's grim up North.

    :D
  • Chiggy
    Chiggy Posts: 261
    How to find North on a sunny day.

    This method is not possible with a digital watch, so the military issue analogue 'dially hands' wristwatches.

    Point the hour hand at the sun. Midway between the hour hand and Twelve is South, so the opposite direction is North.

    In BST, compensate by using midway between the hour hand and 1 o'clock as South.


    As far as I'm concerned, Midday is when the sun is vertically aligned at the Greenwich Meridian. In GMT, this is south.
    North is 180.0000 Degrees away from this.
  • bompington
    bompington Posts: 7,674
    Chiggy wrote:
    How to find North on a sunny day.

    This method is not possible with a digital watch, so the military issue analogue 'dially hands' wristwatches.
    Err, they also issue compasses...
  • StillGoing
    StillGoing Posts: 5,211
    It's also worth noting that magnetic north swaps with the south every once in a while according to research. Wouldn't fancy being in the middle of some lone expedition when that happens.
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
  • StillGoing
    StillGoing Posts: 5,211
    Chiggy wrote:
    How to find North on a sunny day.

    This method is not possible with a digital watch, so the military issue analogue 'dially hands' wristwatches.

    Point the hour hand at the sun. Midway between the hour hand and Twelve is South, so the opposite direction is North.

    In BST, compensate by using midway between the hour hand and 1 o'clock as South.


    As far as I'm concerned, Midday is when the sun is vertically aligned at the Greenwich Meridian. In GMT, this is south.
    North is 180.0000 Degrees away from this.

    You must have been out of the military for a long time as they stopped issuing G10 watches even when I was in and I left in 1990. If you're ver so lost that you need to resort to using an analogue wrist watch to tell which way north is, you seriously shouldn't be allowed out on your own.
    I ride a bike. Doesn't make me green or a tree hugger. I drive a car too.
  • Pross
    Pross Posts: 43,463
    :oops: Always getting my astrologicals and astronomicals mixed up, worst thing is I even thought about it before opting for astrological!
  • snailracer
    snailracer Posts: 968
    North is uphill, innit?
  • Dave Cornwall
    Dave Cornwall Posts: 56
    Grid North and True North should be the same. When measuring a bearing on a map or chart you would align the protractor with the longtitude line, or the Eastings (vertical lines) on an OS map, in order to get a true bearing.

    In order to steer, walk or drive along that bearing using a compass, you then have to apply the compass variation to get magnetic north.

    The earths core is basically a lump of molten iron, which creates a magnetic field. Unfortunately the magnetic North is different from true north, hence the variation. And it changes gradually over time, as well as the massive reversals every 70,000 years or so. Apparently we are overdue a change!

    Depending upon your position on the earths surface this variation will be different, it may be to the east of true north, to the west or even aligned with it. In the UK the variation is roughly between 3.5 degrees west and 2 degrees west. If you are at the North Pole, magnetic North will be due south of you!

    If the magnetic variation is west, you add the variation to the true bearing to get the magnetic heading. If it to the east, you subtract the variation from the true bearing.

    I could go on, but you've probably all gone a bought a GPS by now, which does it all for you!

    Dave B
  • snailracer
    snailracer Posts: 968
    Dave Cornwall wrote:
    Grid North and True North should be the same...
    Dave B
    True north moves with respect to grid north. Apparently, 20m since 1900.
  • Weejie54
    Weejie54 Posts: 750
    If the magnetic variation is west, you add the variation to the true bearing to get the magnetic heading. If it to the east, you subtract the variation from the true bearing.

    Not forgetting deviation, of course. Probably of some significance if you have a steel framed bike.
  • Ron Stuart
    Ron Stuart Posts: 1,242
    You got a problem coming chaps..... http://survive2012.com/index.php/geryl-pole-shift.html Olympics 2012 in southern hemisphere :!: :shock:

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