Declination Verification

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coazon de oro
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Declination Verification

Post by coazon de oro » Wed Mar 09, 2011 12:12 am

Hell O TradClimber,

I didn't know where to place this question. Thinking it may be the cause of someone getting lost, I placed it here.

I have known the declination in my area to be 5 degrees for some time. I live in south Texas.

I was trying to verify this with my compass last night, but found no difference between true north, and magnetic north. I live in a ranch where the north star is very visible.

Had I been using a map that day, I would have allowed for the 5 degrees, and easily been lost.

The margin for error is greater in other areas, if one relies on old declination charts, I would assume.

Have you checked the declination in your area lately?

Homar P. Olivarez

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hikin_jim
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Re: Declination Verification

Post by hikin_jim » Wed Mar 09, 2011 10:39 am

Homar,

That's very strange that your magnetic compass would show the same bearing as true north in south Texas.

I just checked the USGS Declination Calculator. I used zip code 78520 (Brownsville) to get the latitude and longitude. The declination for Brownsville, TX, is 4° 30' E. In other words, your compass should point five degrees to the right (east) of true north. If your compass is pointing to true north instead of five degrees to the right, that's generally a problem.

There are several reasons why this might happen:
1. Metal near you. Were you wearing a steel watch band? In a car? Had a pen in your hand? Wearing rings? In a building? Any ferrous (iron based) metal can affect a compass. Ideally, you want to be outdoors, away from any large metal structures or objects, with nothing but the compass in your hands when you take a bearing.
2. Local iron ore deposits. If there are a lot of minerals in your area, mineral deposits (iron ore specifically) can affect your compass. You could try taking bearings other places in your general area and seeing if the apparent error persists.
3. Your compass is adjustable. Probably not, since relatively few compasses are adjustable, but if you have a nicer-than-average compass it might be adjustable, in which case it's working perfectly.
4. Lastly, maybe you've got a bad compass. Have you compared the bearing from your compass to another compass?

Of course, hopefully you've verified that you were looking at the correct star and all that sort of thing, yes?

HJ
Last edited by hikin_jim on Thu Mar 10, 2011 1:41 pm, edited 1 time in total.

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Re: Declination Verification

Post by GeorgeW » Wed Mar 09, 2011 12:15 pm

Declination in my area is listed at being 11 degrees but I really don't use that information when I'm in the field.

I always have a topographical map with me that I use to identify peaks/ravines and from which I can discern my location. Sometimes I'll shoot an azimuth from where I'm standing to something I want to find on a cliff or steep hillside. Then I can approach from the top of the hill/mountain and use a back azimuth to my previous spot to let me know if I'm left, right, or right on target.

The only time I'd need to use declination is during night navigation when it's tough to make out the terrain. However, it's tough enough to find things here during the day. I wouldn't want to try to find things at night.

Someday I should get a GPS but I'm comfortable with my maps and compass and it never needs batteries.

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Re: Declination Verification

Post by hikin_jim » Wed Mar 09, 2011 12:47 pm

GeorgeW wrote:Declination in my area is listed at being 11 degrees but I really don't use that information when I'm in the field.
Just for fun, I looked up the declination for Mesa, AZ. The declination for Mesa is 10° 55' E -- eleven degrees easterly in other words. You're right on, George.

Unless you're shooting bearings on the ground and then plotting them to a map (or vice versa), it's usually not too critical to know the exact declination.

Usually when I orient my map (turn my such that the terrain on the map is facing the same direction as the terrain I'm actually in), I just plop my compass down such that the magnetic needle lies to the right of true north. It's good enough for general terrain orientation. If I'm doing something tricky like trying to find an old, abandoned trail or something, then I'll do something far more precise.
GeorgeW wrote:Someday I should get a GPS but I'm comfortable with my maps and compass and it never needs batteries.
You too? Never have bothered to get my own GPS. That's why you bring people with you on a hike. :lol: Although honestly, I very rarely ever want to look at a GPS.

HJ

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coazon de oro
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Re: Declination Verification

Post by coazon de oro » Thu Mar 10, 2011 12:28 pm

HJ,

Here I was, thinking I was the only one without a GPS.

My zip code is 78014, which has a declination that rounds out at five degrees.

I have never worn a watch, rings, or any other bling other than a custom folding knife. I have plenty of metal in my body, but it's not magnetic.

I had checked my compass with two other ones some time ago.

I took your advice, and took bearings from another area. Declination verified at five degrees. Thanks for the tip.

Now I wonder whats effecting my compass at that other spot? May pull out the metal detector.

Homar P. Olivarez

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Re: Declination Verification

Post by hikin_jim » Thu Mar 10, 2011 1:44 pm

coazon de oro wrote:I took your advice, and took bearings from another area. Declination verified at five degrees. Thanks for the tip.
Cool. :) Mystery solved.
coazon de oro wrote:Now I wonder whats effecting my compass at that other spot? May pull out the metal detector.
That might be interesting. You could also look at the USGS mineral maps for your area. Let us know what you find out.

HJ

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Re: Declination Verification

Post by hikin_jim » Thu Mar 10, 2011 1:47 pm

Here's an interesting chart showing North America and what the various declinations are. Declinations are westerly instead of easterly on the east coast. Gotta remember such things if you're hiking while traveling.

Image

HJ

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Re: Declination Verification

Post by TradClimber » Wed Mar 16, 2011 12:17 pm

The Trad in TradClimber is Tradional.

However, I'm not so traditional - as to not embrace a new technology that enhances my enjoyment and safety in the outdoors. GPS receivers has done both.

With a GPS it's simple to have the current magnetic declination from true north for most any place on earth where you have a clear view of the sky.

A GPS is a fine supplement to your map and compass.

TradClimber

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Re: Declination Verification

Post by hikin_jim » Wed Mar 16, 2011 1:12 pm

Yeah, I know I'm a luddite. It's just that I have too much outdoors CRAP* as it is, and I'm fairly good with maps.

HJ

*CRAP = Camping Related Accessories and Peripherals.

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Re: Declination Verification

Post by cubfan64 » Wed Mar 16, 2011 1:41 pm

For what it's worth, I like having a GPS, but I struggle to make sure I don't rely on it constantly while out hiking. If I do that, I find that I am more casual in watching my surroundings as well as looking at maps and using a compass, and I DON'T LIKE to find myself relying on any piece of technology.

For me at least, I liken it to what happened to mathematics when calculators came out. Eventually students stopped learning the "basics" of how and why math problems can be solved by hand and started relying on calculators (and now I suppose spreadsheets) to do all the work.

That's why so many kids today can't make change at the cash register if it doesn't tell them exactly how much to give out.

Off topic, but a similar rant against technology... I work in a chemical laboratory and we just hired a recent college graduate and found out later that he had spent a grand total of a semester or two (at most) ACTUALLY IN A LABORATORY setting! Almost all of his "lab" classes were done on a computer with software packages to simulate hands on lab work. He had only the vaguest idea of what different pieces of glassware were called, how they connect together and all the other basic information we expected a lab technician should have.

What a sad state of affairs!

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