Determining declination

J

jw2n

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Throughout the 70s until I retired from the Army a few years ago, I would receive exhaustive classes on land nav, and participate in many courses. Declination was always covered in detail, and how to determine it. Recently an idea poped in my head that I have never been taught. If you were in an unknown location with a compass and needed to determine declination could you use the North Star? As I understand it, it never varies by more than a degree from true north. I know that trying to get an accurate reading between your compass and the star, and in the dark could be fun, but would it not work? Declination, esp in the NE and NW USA gets pretty extreme.
 
my understanding concerning declination is that in situations traveling up to 15 or 20 miles, declination is a minor factor. one traveling hundreds of miles probably needs a map of the territory which has the declination marked for that part of the state or country.
dennis
 
jw2n said:
Throughout the 70s until I retired from the Army a few years ago, I would receive exhaustive classes on land nav, and participate in many courses. Declination was always covered in detail, and how to determine it. Recently an idea poped in my head that I have never been taught. If you were in an unknown location with a compass and needed to determine declination could you use the North Star? As I understand it, it never varies by more than a degree from true north. I know that trying to get an accurate reading between your compass and the star, and in the dark could be fun, but would it not work? Declination, esp in the NE and NW USA gets pretty extreme.
Click to expand...

I believe Ron Hood covered that in his navigation video. And yes, it does. BTW, excellent video and you can also learn about the Ottomani Sun compass. :thumbup: :D

As far as lining up the North Star in the dark, he used sticks stuck in the ground as pointers (he lined up the two sticks with Polaris). You could complete your calculations the next day in the light.

Doc
 
Interesting thought for sure. I can't figure why it wouldn't work, at least better than nothing. I think a single degree of error leads to 90 feet of horizontal error per mile. In NW Montana declination is ~15deg E (so not using it could put you nearly a quarter mile off track just within the first mile of travel.
 
Anyone use this? I printed this and keep it with my compass and also consult land surveyor or university on the declination of a area before I head to a certain area. I dont know about how to determine it with the north star, but will look into it. Seems interesting

Magnetic_Declination.jpg


Saw a better map on Wikipedia.

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

What do you guys think about the Wiki explanation on things?
 
Declination is only needed if you're going to use a compass with a map. If you're just using a compass "stand-alone" only then you do not need it. However you need to make sure everyone on your team/party are using the same declination. Generally just place the Declination to 360 so everyone is on the same page.

So if you're using a Map and you do not have a current Declination then just use the printed declination listed on the map. Granted it will be dated and off but at least you have a starting point. Declination drifted at my particular location 8' (8 minutes) over ten years. So that equates to about one full degree in a ten year time span. Most of us deviate up to 5 degrees when we're trudging around in the woods anyway - we cannot hold a true +/- 5 degrees unless we're on level flat ground with no obstacles and plenty of recognizable landmarks/waypoints. Granted you can be off by a mile or two from your target destination if you are traveling great distances. However, today there are plenty of roads and significant way-points you can adjust as you travel using Resection or Intersection. Besides with me knowing my location drifts by 8' per year I can adjust by doing some simple pencil math.

Here is the NOAA Gov Web Site to input your Zip Code or Lat/Long to get an "up-to-date" Magnetic Declination before you enter a given area for travel - http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp

BTW guys, I think you're confusing True North and Magnetic North. Ron's video talks about how to calibrate your Ottaman Sun Compass with the Sun or True North and NOT Magnetic North which is shifting annually. Yes, you can use a sun compass to get a rough idea of True North but it not the same as Magnetic North.

Again, Magnetic North - declination is only needed when one is interfacing a compass and/or GPS with a map. If you're going to just land nav by compass only it isn't needed. That is why something as primative as a stick sun compass is effective as it doesn't require the use of declination.

Here is a calculator to use to determine how much declination has drifted/shifted in your particular area over a given time frame (you set the parameters) - http://www.ngdc.noaa.gov/geomagmodels/IGRFWMM.jsp
 
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Yes, the OP is exactly correct. If you can see the North Star, you have a phenomenally accurate alignment to true North. Finding Polaris is, IMO, one of the most essential navigation skills because it is so accurate and indicator, and can be used for many other navigational needs.

The problem, of course, is that Polaris isn't always visible (daytime and inclement weather).

The OP also brings up a good point that compass users should be checking their alignments to fixed objects all the time when orienteering. Not just the North Star, but to anything else that will work to keep you on line and on task.

But, yes, as others agree: declination is only the difference between True North and Magnetic North. Unless you're very close to the NMP, short hikes do not always get affected by declination. Consult your map, etc. You all know what to do.
 
Quirt said:
Declination is only needed if you're going to use a compass with a map. If you're just using a compass "stand-alone" only then you do not need it. However you need to make sure everyone on your team/party are using the same declination. Generally just place the Declination to 360 so everyone is on the same page.

So if you're using a Map and you do not have a current Declination then just use the printed declination listed on the map. Granted it will be dated and off but at least you have a starting point. Declination drifted at my particular location 8' (8 minutes) over ten years. So that equates to about one full degree in a ten year time span. Most of us deviate up to 5 degrees when we're trudging around in the woods anyway - we cannot hold a true +/- 5 degrees unless we're on level flat ground with no obstacles and plenty of recognizable landmarks/waypoints. Granted you can be off by a mile or two from your target destination if you are traveling great distances. However, today there are plenty of roads and significant way-points you can adjust as you travel using Resection or Intersection. Besides with me knowing my location drifts by 8' per year I can adjust by doing some simple pencil math.

Here is the NOAA Gov Web Site to input your Zip Code or Lat/Long to get an "up-to-date" Magnetic Declination before you enter a given area for travel - http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp

BTW guys, I think you're confusing True North and Magnetic North. Ron's video talks about how to calibrate your Ottaman Sun Compass with the Sun or True North and NOT Magnetic North which is shifting annually. Yes, you can use a sun compass to get a rough idea of True North but it not the same as Magnetic North.

Again, Magnetic North - declination is only needed when one is interfacing a compass and/or GPS with a map. If you're going to just land nav by compass only it isn't needed. That is why something as primative as a stick sun compass is effective as it doesn't require the use of declination.

Here is a calculator to use to determine how much declination has drifted/shifted in your particular area over a given time frame (you set the parameters) - http://www.ngdc.noaa.gov/geomagmodels/IGRFWMM.jsp
Click to expand...

If your reference was to me, I wasn't comparing the Ottomani Sun Compass with Magnetic North, merely pointing out another one of his goodies on the video.
Doc
 
I meant to determine true north, not magnetic. With magnetic only, there would not be the need to determine TN.

Actually 26 served, and thank you.
 
With my legendary sense of direction, adjusting for declination wouldn't help one bit... Fortunately, my wife is a natural born homing pidgeon, and has a better head for direction than I do.
 
killstrees said:
I think a single degree of error leads to 90 feet of horizontal error per mile. In NW Montana declination is ~15deg E (so not using it could put you nearly a quarter mile off track just within the first mile of travel.
Click to expand...

Here in western Massachusetts declination is 15° West. So if I go to Montana and assume the difference in declination isn't worth bothering with, my compass will seem to be 30° off.
 
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