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skywatcher
2003-Jun-09, 05:34 PM
Apparently some people have notcied there compasses 5 degrees off to the north east, but the problem is I saw this on Godlike so not sure about it, has anyone had the same thing .

http://66.242.35.139/bbs/message.php?message=53371&mpage=1&topic=3 :o :o

Eta C
2003-Jun-09, 05:39 PM
Off from magnetic north or true north? I don't expect the gang at that site to know the difference given the scientific knowledge they've displayed. Magnetic compasses point to the north magnetic pole which is located in northern Canada. Depending on where you are on the Earth, the correction can be huge. Near the geographic north pole, the compass would point south as you're north of the NMP. A better question is does the compass shift from day to day? If so at what rate? I doubt they have answers to these questions because they haven't thought of them. I'll tell you right now the answers are no and 0 (at least on a day to day basis. Over the life of the earth on a scale of thousands of years the NMP has shifted).

Donnie B.
2003-Jun-09, 06:00 PM
Actually, magnetic north moves a good bit faster than "on the scale of thousands of years". Navigation charts include correction factors for the pole offset, and these are revised every few years. Sensitive instruments can detect movement on the scale of weeks or months, I believe.

Added: from http://www.ptarmigans.org/magnetic.html


The NMP was first physically located in 1831 at a point over 1000km south of its current location. It is now drifting north/northwest across the Canadian Arctic at the relatively fast rate of 40 km per year, or approximately 350 feet per day. At present course and speed (neither of which is accurately predictable in the long term) it will reach Siberia in about 50 years.

Of less consequence to most compass users but still of interest (hmmm, I may be making assumptions here) is that, in addition to its long term secular change, the NMP also moves in a daily elliptical path around its average, or “official,” location. This movement results from magnetic field fluctuations caused by charged particles emitted by the Sun. On a day of high solar disturbance, the NMP might travel up to 80 km from its average location. This means that, near the NMP, declination not only might change by several degrees each day, but may switch between east and west declination. Now that would make for some tough routefinding! In fact, as an Arctic traveler approaches the NMP the reliability of a compass declines until it eventually becomes useless.

Eta C
2003-Jun-09, 06:07 PM
Actually, magnetic north moves a good bit faster than "on the scale of thousands of years". Navigation charts include correction factors for the pole offset, and these are revised every few years. Sensitive instruments can detect movement on the scale of weeks or months, I believe.

True, but what's the rate? I'll wager it's in the milliradian per year range. The point is that it won't come close to accounting for the 5 degrees per day the panic mongers claim to see. What's typical of their thinking is to take a known fact (the magnetic poles do drift) and a poor observation (gee, from where I sit in northern Canada my boy scout compass doesn't point to the pole star) and put together an unwarranted conclusion (the crust is shifting at an alarming rate!).

Byrd
2003-Jun-09, 06:36 PM
I'm going to argue for imagination/cat/dog/bumping on the Mysteriously Moving Compass -- and here's why:

I do geocaching (that's hunting down benchmarks and "treasure troves" left by other geocachers worldwide) and to do this you need a handheld GPS (Magellan Platinum... LOVELY thing and has saved my fanny soooo many times with its street map uploads). You use satellite GPS positioning, but you also set your maps by true north and magnetic north (the GPS may know where on the Earth you are, but it can't line up a street map set properly without knowing where North is.

I haven't noticed any significant drift.

Furthermore, on the geocaching forums (http://ubbx.groundspeak.com/6/ubb.x), there's no great fret and storm about what's going on and why the magnetic poles are so far off. These folks do geocaching every weekend (and some every day) and would notice if the thing's gone wonkers.

There's no growls and yowls from survey teams.

In short, "Local User Interface" problem is the best answer. And, BTW, if she put electrical equipment on the other side of the wall (moved the refrigerator, microwave, etc) she might certainly get anomalous readings.

kilopi
2003-Jun-09, 06:39 PM
I'll wager it's in the milliradian per year range.
Yes, but can be a bit more. Depends on where you're at, too. A milliradian per year is one degree in about seventeen years.

Hamlet
2003-Jun-09, 08:39 PM
I'm going to argue for imagination/cat/dog/bumping on the Mysteriously Moving Compass -- and here's why:

I do geocaching (that's hunting down benchmarks and "treasure troves" left by other geocachers worldwide) and to do this you need a handheld GPS (Magellan Platinum... LOVELY thing and has saved my fanny soooo many times with its street map uploads). You use satellite GPS positioning, but you also set your maps by true north and magnetic north (the GPS may know where on the Earth you are, but it can't line up a street map set properly without knowing where North is.

I haven't noticed any significant drift.

Furthermore, on the geocaching forums (http://ubbx.groundspeak.com/6/ubb.x), there's no great fret and storm about what's going on and why the magnetic poles are so far off. These folks do geocaching every weekend (and some every day) and would notice if the thing's gone wonkers.

There's no growls and yowls from survey teams.

In short, "Local User Interface" problem is the best answer. And, BTW, if she put electrical equipment on the other side of the wall (moved the refrigerator, microwave, etc) she might certainly get anomalous readings.

Same here. My GPS unit still shows North where it's always been. I work for a company that produces georeferenced aerial images and none of the images we've shot this spring have shown any deviation from what is expected. Too many people use a compass for something this drastic to go unnoticed.