Earth's magnetic field

[Hardy Heinlin]

4 years later ...

I was just updating the magnetic variation for the final PSX world, and while checking the result, I noticed on those screenshots at the thread start above the isogonic lines are horizontally mirrored. This is not a PSX error, it's just a map test display error (west/east, plus/minus).

I.e. the magnetic southpole should be south of Australia.


Cheers,

|-|ardy


P.S.: Gentlemen, please disregard that early Alpha screenshot of the whiskey compass; the inclination effect there was way exaggerated :-)

[farrokh747]

Something seems to be changing.....

https://www.nature.com/articles/d41586-019-00007-1

http://www.geomag.bgs.ac.uk/research/modelling/WorldMagneticModel.html

https://www.sciencealert.com/shifts-in-the-magnetic-field-force-changes-to-an-important-global-navigation-model-a-year-early    edit: added

The NOAA site is down....

https://governmentshutdown.noaa.gov

fc

[cagarini]

It's a very interesting subject, and one I've been tracking since a long time fc.

The part I probably should, but hadn't actually thought about was the consequences over navigation.

I think the future will probably become a lot more dependant on machinery for tracking than on our Mother Earth magnetic field(s)...

[G-CIVA]

I too have been following this phenomena with great interest.

In my former life I used paper maps & even VFR topographical aviation navigation charts of varying scales & a hand held magnetic compass daily; orientating the former to the ground & walking on a magnetic bearing with the latter having added the Magnetic Variation to the Grid Bearing taken directly from the map - much of this life was spent using this perishable skill during the pre hand held GPS era.

An additional factor had to be added to the local Magnetic Variation for every year after the published date of the map to cater for the continual Magnetic Declination in that area of the planet I was working in at the time. 

In some areas of the planet the Magnetic Variation has to be subtracted from the Grid Bearing to gain a correct Magnetic Bearing.

This Magnetic Variation was almost always added to the Grid Bearing taken from the map to give a correct Magnetic Bearing to walk on.

The old adage we used was "MAG to GRID - GET RID" (or subtract the Magnetic Variation) & "GRID to MAG - ADD" (or add the Magnetic Variation).

This illustration shows clearly how much the Magnetic North Pole has moved in the last 120 years & how much this movement has increased dramatically in the last 30 years.



As those 'Astronauts & Engineers' amongst us will know there are actually three Norths:

True North - Where the actual North Pole is also known as the North Pole.

Magnetic North - Where the Magnetic North Pole is situated.

Grid North - Which is a navigational term referring to the direction northwards along the grid lines of a map or chart projection.

With the continual shift of Magnetic North there may well come a time when we shall have to subtract the Magnetic Variation from The Grid Bearing to gain a correct Magnetic Bearing in all parts of the planet.

[torrence]

Magnetic compasses etc. may seem out of date in a 'GPS world' indeed.  But it's worth remembering that machines and electronic can break, satellites may fail (or be shut down).  In a post-apocalyptic world my survival kit would include (at least): magnetic compass, slide rule, Nautical Almanac, C&H handbook (math and trig tables), current world map (waterproofed), a nautical chronometer, and a small telescope (Galilean satellite eclipses for longitude determination).  I heard an interview with the chap who recently completed a solo walk to the S. Pole - he said he used his hand magnetic compass to keep walking straight in bad visibility conditions.

Cheers
Torrence

[Hardy Heinlin]

... and a small telescope (Galilean satellite eclipses for longitude determination).

Sounds interesting. Why wouldn't you use the chronometer and a star map to determine your longitude? Is it to check the chronometer's accuracy?


Cheers,

|-|ardy


P.S.: Are there any GPS and gyro based compasses that determine the true heading solely by recording the GPS position progress and translating this record to a long term direction reference stored in a gyro? If so, I guess the precision of this device will depend on how far you travelled since the last activation of the device; without a position progress the device cannot determine any heading at all.

[torrence]

Star maps are great for latitude, but they don't tell you the time in Greenwich, or Paris.  The story of the development of the chronometer is very well told in Dava Sobel's "Longitude: The True Story of a Lone Genius Who Solved the Greatest Scientific Problem of His Time".  John Harrison won a prize for developing the first practical nautical chronometer - to win, his device had to be carried across the Atlantic and it's derived longitude compared with - that derived from Galilean satellite eclipses (using telescopes carried on the same voyage and set up at the ship's position after landfall). Required accuracy was agreement within one minute of time/longitude - "a minute's a mile the world round".  There's a good reason we're still using nm and knots. 

Bowdich's 'method of lunars' was a competing way of getting longitude but required difficult lunar observations and lengthy calculations that were beyond the capabilities of most working ships' captains.  Harrison chronometers rapidly became a fixture on every ship's bridge - still are if you don't want to bet you're life that the GPS etc. etc. won't go out.

So to answer your question, Hardy.  A chronometer is great but has to be reset based on some other time signal eventually.  In my post apocalyptic world I assume the BBC might not be available and I'd have to set my chronometer from satellite eclipses. 

Cheers,
Torrence 

[G-CIVA]

Some more Apocalyptic Top Tips ....

For you post apocalyptic survival kit can I recommend the following two items which will NEVER let you down:



The military style SILVA lightweight compass measures in MILS instead of DEGREES.  The advantage of MILS over degrees for land navigation is sheer accuracy.  You will notice that on the inside of the rotating compass dial that DEGREES are also printed should you require them.

A MIL is one metre of arc subtended over a radius of 1000m from the point of person viewing & there are 6400 MILS in a full circle subtended at that radius of 1000m.  It is the standard measurement for land navigation for most Western military organisations.

To assist you in this you it would be worth purchasing one of these:



This type of protractor will assist you in calculating bearings & correctly from a map sheet & it will help enormously when exactly calculating Grid References in various Map Scales.

Both products are accurate, light weight, relatively cheap & very very easy to master.  A decent modern hand held GPS system can be set up to use MILS as the primary heading reference, using local map sheet datums, the Military Grid System or MGRS which is a mapping system whereby the entire planet has been mapped in 1:50 000 & 1:100 000 scales.  Hand held GPS can indeed be used with LATLON coordinates in varying levels of accuracy if the user is proficient.

I successfully used these products during my long career in a former life with alarming accuracy & also in conjunction with my now ageing Garmin GPS12XL using all three navigational formats. I still have all 3 of these tools for navigation & will always keep them for future use.

Both products are available here:

https://picclick.co.uk/Protractor-Ra-6-Genuine-British-Uk-Mod-Nsn-171868730102.html

https://www.ebay.com.au/p/SILVA-Expedition-Military-4-Southern-Hemisphere-Plate-Compass/1540177700?iid=292920968179&chn=ps&thm=1000

Finally,

I could take up hours explaining this ... but a picture paints ... always wear a chronograph if you can ... but remember you can recreate the face of a clock with sticks or objects which make straight lines ...

https://youtu.be/BoKQMwUx2gA

[Hardy Heinlin]

So to answer your question, Hardy.  A chronometer is great but has to be reset based on some other time signal eventually.

I thought so. It can't run forever at high precision without any recalibrations from time to time. I overlooked the fact that an apocalyptic era may last very long ... :-)


Cheers,

|-|ardy

[cagarini]

Regarding Apocalyptic Top Tips, as Steve put's it :-)

There's this interesting one from a more or less well known YouTube channel:

https://www.youtube.com/watch?v=zgJ4zVNe_vk&t=0s&index=8&list=PLHSoxioQtwZfY2ISsNBzJ-aOZ3APVS8br

[mgeiss]

Best ask some people who survived an apocalypse before, they should know.