NOAA magnetic declination web site

[Corey]

I ran across this web site when I was looking for a digital compass:

NOAA's Geophysical Data Center - Geomagnetic Data

The interesting thing is that the calculated declination for my location is 1 degree off of what the chart shows on the installation page on Sadoun's web site. This NOAA site says my declination is 16.55E, while the chart on the web site shows -17.6 (or so) for my location which is Portland, Oregon (45.5N, 122.9N)

The NOAA site says that my declination is drifting by 9' W per year. Given that Sadoun's chart was made in 2004, and if the drift has remained constant, that would be about 27' of drift, or about 0.5 degrees. So maybe the drift rate has changed a bit.

In any case, the above web site might be a more accurate reference.

[boroda1]

Personally, using this one:
hxxp://geomag.usgs.gov/models/models/

(It calculates very precise for evry year{EDIT} and date {/EDIT}, and also converts geolocation data from min' sec" format to decimals on the fly)

[Corey]

That's an interesting site.

By the way, I realized that I made a mistake... my declination from that site is 16deg 55minutes, not 16.55. So the difference between that and the 2004 chart is only about 0.7 degrees.

Not a huge deal, but it can't hurt to start with a more accurate number.

[rainman]

Originally Posted by Corey

That's an interesting site.

By the way, I realized that I made a mistake... my declination from that site is 16deg 55minutes, not 16.55. So the difference between that and the 2004 chart is only about 0.7 degrees.

Not a huge deal, but it can't hurt to start with a more accurate number.

most of the numbers just gets you in the ball park the final tweaking is whats important because seems like no two dishes set's up exactly the same.

[wejones]

Originally Posted by rainman

most of the numbers just gets you in the ball park the final tweaking is whats important because seems like no two dishes set's up exactly the same.

Right. Plus many places have significant local variations that are bigger than these errors. I went out in my woods once to a place where I can see a mountain that's 35 miles away, and took a bearing on the mountain, then moved about 5 or 10' and took another bearing, and there was about a 5 degree difference. This was about a quarter mile away from the nearest building or anything. I also have one compass that just wanders around by 15 degrees or more, just sitting there. So I wouldn't trust any compass reading more than to a couple degrees accuracy. If you want accuracy, you should use the sun or moon.

[rainman]

Originally Posted by wejones

Right. Plus many places have significant local variations that are bigger than these errors. I went out in my woods once to a place where I can see a mountain that's 35 miles away, and took a bearing on the mountain, then moved about 5 or 10' and took another bearing, and there was about a 5 degree difference. This was about a quarter mile away from the nearest building or anything. I also have one compass that just wanders around by 15 degrees or more, just sitting there. So I wouldn't trust any compass reading more than to a couple degrees accuracy. If you want accuracy, you should use the sun or moon.

agreed Bill the sun works real nice.

[Corey]

What is this "Sun" thing you speak of? I live in Portland, Oregon. (That's not a non-sequitur)

[rainman]

Originally Posted by Corey

What is this "Sun" thing you speak of? I live in Portland, Oregon. (That's not a non-sequitur)

check www.srrb.noaa.gov
has a nice solar caculator on their site.

[slotzero]

It does seem that using the sun would be much easier... one would think if you were handy with cardboard and a hobby knife you could probably get the elevation too, no?

[rainman]

Originally Posted by slotzero

It does seem that using the sun would be much easier... one would think if you were handy with cardboard and a hobby knife you could probably get the elevation too, no?

I do believe that has been done.

[Corey]

We don't see the sun here much this time of year.

I'd have to launch a rocket with a video camera and telemetry to 10,000 feet. The rocket would have to be equipped with attitude and rotational angle sensors so that I could monitor and calculate the position of the Sun using the video feed.

Easy!


(P.S. I do appreciate the link, though. There are times when we do get brief clear skies... at night)

[Corey]

The weather, as usual, has made me a filthy, stinking liar About an hour after I posted, the Sun has come out, and there're just a few wandering clouds now.

(P.S. To be perfectly honest, the weather didn't add the filthy and stinking part)

[rainman]

the weather will do that to you. as we say around here if you don't like the weather wait a minute and it will change.LOL