understanding and compensating for magnetic declination

hey - once again i has been dragged kicking and screaming into providing free navigation training for a mates progeny

though thats not what this thread is about

however yerstadys topic was magnetic declination [ and the difference between true , magnetic and grid north ]

and as a teaching aid - i found :

source

a quite nifty little website that does the mathematics for you - and displays the parameters in relation to a map

OK - its UK specific so it wont help ferriners calculate the correct offsets for thier location - but it is still a bonkers teaching // learning aid wherever you are in the world if you are attempting to instruct others or get your own head around the concept

of course - google might lead you to a similar resource specific to your country - if you find one - feel free to start a list

thats all folks - enjoy

About -6 in Michigan.


www.thecompassstore.com...

a reply to: ignorant_ape

Magnetic poles don't stay still so you'd need up-to-date local corrections no matter where you are for high precision navigation. For less precise needs I can get by with a detailed map and solar observations when not being spoilt by things like GPS in the local surrounds anyway. Sailing to a destination 10000km away needs a bit more accuracy than walking through a few valleys.

Older maps are not reliable for magnetic navigation. I'm sure there's some way to put in a variable depending on your start point, but who wants to do More math. LOL

a reply to: Snarl

Maps are aligned to geographical poles so you only need to correct when using a magnetic compass in conjunction with a map.

a reply to: Pilgrum

british OS maps are alligned to the " national grid " - a matrix of 100km squares - that thus allows a consistent 1m acurate cartesian co-ordinate anywhere in the british isles - see pic :



it has many advantages and few drawbacks

a reply to: ignorant_ape

Didn't know that. I've never come across a map here in Oz that wasn't aligned to geographic poles - they all have a magnetic correction printed on them but you'd need to get a new map on a regular basis every few years to avoid errors if you didn't familiarise yourself with any updates. GPS is making this sort of navigation old hat anyway and our grandkids will be lost if the satellites ever fail

Even the bushwalkers here now carry pocket GPS units instead of compasses.

a reply to: ignorant_ape

So, how do I calculate the position of my destination after the "pole shift" which a lot of people,say is coming.
Can you give any base line figures for the new locations of the poles ?

It isn't too far off here in the UP. But is it a mess around Montana.

Interesting topic, that true north and magnetic north stuff.

I have tried to explain it to many people, but it's difficult for them to fathom because they have never used a map that's worth 10% of what they paid for it.

Real maps are curiosities that people buy at flea markets, frame and hang on the wall.

What a waste.

a reply to: tinymind

i would advise :

stop worrying about poleshift fantasies being peddled by doom porn cockwombles

a reply to: tinymind

Good to see some folks learning and using the basics. It used to amaze me how few people new about declination.

Can't declination be determined by magnetic readings and astronomical observation, an accurate time piece and a known location with a bit of math thrown in there?.

I used to know how to do this, but it has been 30 some odd years since I used it.

I used to be a surveyor in the military before the use of GPS became to go to.

a reply to: ignorant_ape

I'm not really worried about polar shift or much of anything else. I just thought I would be the first to bring it up before some "nut job" that really does concern themselves with such.
I would really rather trust my navigation skills of using the stars and moon as reference points. I might get off a few yards but not enough to hinder a good walk.
I still have my old E6B from way back when. It is the handiest computer a man could ever get.

originally posted by: tinymind
a reply to: ignorant_ape

So, how do I calculate the position of my destination after the "pole shift" which a lot of people,say is coming.
Can you give any base line figures for the new locations of the poles ?

I'm not worried about a pole shift but I would assume if one did happen that there's no way to predict the locations of the new poles in advance. Regardless, it's a good idea to familiarize yourself with the pole stars (the north star in the northern hemisphere) and if you're REALLY worried you can teach yourself celestial navigation. This could also come in handy because if you learn the basics you can also learn how to build a giant calendar (like Stonehenge) just in case that pole shift destroys civilization plus it's good to use more math in everyone's life. It helps other people laugh at my occasional math joke (otherwise the worst type of joke there is).

ok - purely as an exercise in thinking


" post pole shift " calculations - my opinions

1 - the sun // polaris [ assuming northern hemisphere ] - will in a single day [ assuming clear skies ] - allow you to determine - " true north "

do NOT use a compass at this stage - only use a map , a watch // clock [ assuming you trust it to be accurate ] and known land marks - to determine if polaris really is still above the true north pole - and if the sun really is " due south " at local noon [ bonus if you have an almanac that gives the suns rise // set bearings ]

2 - now use a compass to determine the difference between the " new " true north and the magnetic pole

the reason you need to do it in 2 stages is - that you have no a-priori way of knowing if the earths axis of rotation [ true north ] has changed independantly - the magnetic pole has changed independantly - or both have " suffered " a different degree of shift

i hope thats clear - will attempt to put up graphics later

but for now - critique ? - can it be done simpler ????

Been trying to remember a method I was shown for estimating North roughly many decades ago and all you need is an analog watch and the sun.

NB This is for the Southern hemisphere so adjust accordingly for the North where you'll be determining South's direction and it's not much use to you at noon if you're in the tropics.

Point the '12' on the watch toward the sun's position, North will be half way between the sun's bearing and the hour hand. Something like that.