Re: [SE] Daytime polar alignment procedure
To: SOLARECLIPSES@AULA.COM
From: FRED ESPENAK <u32fe@lepvax.gsfc.nasa.gov>
Subject: Re: [SE] Daytime polar alignment procedure
Date: Wed, 10 Mar 99 15:35:34 GMT+1

>
>Can a compass,
>along with the local magnetic north correction, be used to
>determine north/south accurately enough?
>

On eclipse trips, I always bring an accurate bearing compass (the kind sold
by marine supply stores). It lets you sight along the horizon and read the
azimuth of north to about 1/2 degree accuracy. Of course, you have to
offset that reading using the magnetic deviation of the geographic
location. You can find this out ahead of time from this web site:

http://www.ngdc.noaa.gov/geomag/declination.shtml

To use it, you just plug in your latitude and longitude and it gives you
the magnetic variation from true north.

When you sight on north with your compass, you must offset using this
value. While taking a reading, I make a mental note some feature along the
horizon which I then call 'North'.

One word of advice: stay at least 20 feet away from anything made of iron,
nickel, steel, etc. when making you compass reading. It could throw off
your reading.

The beauty of this technique is that it works day or night, rain or shine.

This gives you a pretty good rough polar alignment. If you need a better
alignment, I then use the drift method on the Sun (day) or a star (night).
A description of the drift method of polar alignment is at:

http://astrophotography.aa6g.org/Astronomy/articles.html (now missing)

Regards,

Fred Espenak

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Name:    Fred Espenak                   Planetary Systems Branch, Code 693
e-mail:  u32fe@lepvax.gsfc.nasa.gov     NASA/Goddard Space Flight Center
Voice:   301-286-5333                   Greenbelt, MD 20771
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Eclipse Home Page -  http://eclipse.gsfc.nasa.gov/eclipse.html
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This file last edited March 13, 2013 (to update a link).