Peter Mayer wrote:
> On 11/11/98 Greg Milsom wrote,
> >Today I learned that one of the reasons my new dial was not as exact as
> >I had hoped was because the magnetic variation I was using to align the
> >dial was several years old and that magnetic variation does in fact
> >change over time.
You can get precise magnetic declination from several sites in the Internet.In
the end of this message I put a message from Tom McHugh that
points toward geomag, a DOS-based program that calculates the
magnetic declination for several years, any coordenates.
I think among the the URLs I used are: http://geomag.usgs.gov/
On the other hand, I don't think I would use a magnetic compass
to orient a sundial. I think it is too error prone. I would use the
sun itself instead.
I don't know your coordenates and I can not get any hints from your
e-mail address (since it is not based on the ISO (country) schema).
If you are in the Northen Hemisphere, this is a good season to
find the North/South line using the sun since it is now approaching the
tropic in the Southern Hemisphere (Capricorn) and it moon shadow
in the Northen Hemisphere is quite long.
Here is what I would do: use Luke's sun calculator to find
the transit time at your longitude.http://www.gcstudio.com/suncalc.html
Put a short, vertical gnomon. Make sure it is really vertical.
With a precise watch mark the shadow at transit time. The
sun will be due South, the shadow points towards the North.
> Dear Greg,
> It does change, alas. A while ago I created an Excel spreadsheet,
> based on the equations in Meus' book which seemed to get correct answers.
> I only set it up to calculate single days, but that could be modified.
> Since it was created solely for my own amusement, it comes with little or
> no documentation, but if you want to play with it, let me know (and what
> encoding standard your e-mail browser uses) and I can try to send it to
> you.
>
Peter
I am interested in this Excel Spreadsheet. I am right now implementing
fer j. de vries' algorithms (http://iaehv.nl/users/ferdv/definit.htm). One of
the
problems I have is checking every step.
So, a spreadsheet like your may be useful for me to check the results of
my program.
> Peter Mayer
>
> ----------------------------------------------------------------------
> Peter Mayer | [EMAIL PROTECTED]
> Politics Department | 'phone:+61.8 8303 5606/5610
> University of Adelaide | FAX: (+61.8) 8303 3446
> Adelaide, SA 5005 | Time Zone: GMT +9.5 hrs (April-October)
> AUSTRALIA | GMT +10.5 hrs(November-March)
> ----------------------------------------------------------------------
Subject:
Fw: Fw: Magnetic North Pole
Date:
Mon, 28 Sep 98 21:11:26 -0400 (EST)
From:
"Tom Mchugh" <[EMAIL PROTECTED]>
To:
[EMAIL PROTECTED]
References:
1 , 2
Fernando,
I found these e-mails on the subject of magnetic north, dating
from November last year (see quoted material below). I hope
this helps you
Tom McHugh
R. R. 1, Box 896
Fort Fairfield, ME 04742
USA
46N45' 13"
67W48' 42"
****************************************************************************
******************
----------
> Date: Saturday, November 08, 1997 15:25:45
> From: Richard Langley
> To: k.schwarzinger
> Cc: Sundial List
> Subject: Re: Fw: Magnetic North Pole
>
> On Sat, 8 Nov 1997, k.schwarzinger wrote:
>
> > Richard,
> >
> > thank you very much for your answer about the magnetic North
> > Pole.
> >
> > It is very practically to found the magnetic declination for each
> > point of the earth and every year.
> >
> > I have entered the geographical coordinates of my home :
> > Latitude: 47 Degees 14 Min (North) and Longitude: -11 Degrees
> > 27 Min (East) and the year 1997.
> > I got the message :
> >
> > "The magnetic declination in 1997 at Latitude 47 Degees 14 Min
> > N and Longitude -11 Degrees 27 Min W (!) = 0 Degrees
> > 40 Min E.
> >
> > Why -11 W (West?) ! Why is 'East' not indicated ?
> >
> > Karl.
> > [EMAIL PROTECTED]
>
> Karl:
>
> It is very common in North America (except in geodetic circles!) to treat
west
> longitudes as positive. The software was written primarily for the use of
> Canadians hence the sign bias. The geodetic convention is to treat east
> longitudes as positive. Of course, then North Americans would have -66
E! :-)
>
>
> By the way, there is another geomagnetic field program that can be
accessed on
> the Internet. It's hosted by the U.S. Geological Survey and is available
via
> telnet: neis.cr.usgs.gov. Log in ID is QED. This software is not
> "North-American-centric."
>
> Here's the information on how to run the on-line program:
>
> GEOMAG provides values of the elements and parameters of the Earth's
magnetic
> field. The values are estimates based on mathematical models. Values of
the
> following elements and their rates of change are available:
>
> D - Declination (also called compass variation; east declination is
> considered positive, west declination negative)
> I - Inclination (also called dip; downward inclination is considered
> positive, upward inclination negative)
> H - Horizontal intensity
> X - North component
> Y - East component
> Z - Vertical intensity (considered positive downward, negative upward)
> F - Total intensity
>
> Positions of the Magnetic Poles and parameters of the centered and
eccentric
> geomagnetic dipoles are also available.
>
> You will be prompted to select a field model and to enter the date and
> geographic coordinates (latitude, longitude, and elevation) of locations
of
> interest. If you are unsure of how to respond to any prompt, enter a
question
> mark (?) to get help. If you would like the program to back up to the
> previous prompt, enter a caret (^) (that is, the SHIFTed-6 key, not the
> UP-ARROW key). If a default response (shown in brackets) is available
and is
> suitable, you may select it simply by pressing RETURN. To quit the
program,
> press CTRL-Z (hold down the Control key and press Z).
>
> (Reminder: Enter <?> for help, <^> to back up, <CTRL-Z> to quit.)
>
> Options:
> 1 = Field Values (D, I, H, X, Y, Z, F)
> 2 = Magnetic Pole Positions
> 3 = Dipole Axis and Magnitude
> 4 = Magnetic Center
>
> -- Richard Langley
> Professor of Geodesy and Precision Navigation
>
>
>
============================================================================
==
> =
> Richard B. Langley Internet: [EMAIL PROTECTED] or
[EMAIL PROTECTED]
>
> Geodetic Research Laboratory BITnet: [EMAIL PROTECTED] or
> [EMAIL PROTECTED]
>
> Dept. of Geodesy and Geomatics Engineering Phone: (506) 453-5142
>
> University of New Brunswick FAX: (506) 453-4943
>
> Fredericton, N.B., Canada E3B 5A3 Telex: 014-46202
>
> Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/
>
============================================================================
==
> =
>
>
****************************************************************************
********************************************************
****************************************************************************
********************************************************
>On Fri, 7 Nov 1997, k.schwarzinger wrote:
>> Dear all,
>>
>> is there in the INTERNET a website, which gives informations
>> about the curent value from the declination of the magentic
>> North Pole ?
>>
>> Are there still informations about the situation of the magnetic
>> North Pole ( INTERNET or literature ) ?
>>
>> Thanks for any help.
>>
>> Regards
>> Karl.
>http://www.geolab.nrcan.gc.ca/geomag/e_cgrf.html
>===========================================================================
====
> Richard B. Langley Internet: [EMAIL PROTECTED] or
[EMAIL PROTECTED]
> Geodetic Research Laboratory BITnet: [EMAIL PROTECTED] or
> [EMAIL PROTECTED]
> Dept. of Geodesy and Geomatics Engineering Phone: (506) 453-5142
> University of New Brunswick FAX: (506) 453-4943
--
Fernando Cabral Padrao iX Sistemas Abertos
mailto:[EMAIL PROTECTED] http://www.pix.com.br
mailto:[EMAIL PROTECTED]
Fone: +55 61 321-2433 Fax: +55 61 225-3082
15º 45' 04.9" S 47º 49' 58.6" W
19º 37' 57.0" S 45º 17' 13.6" W
