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true north question

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#1 donnie3

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Posted 30 March 2009 - 09:36 PM

whats an easy way to find true north using a compass. does it have to correspond with your location. thanks, don

#2 DonR

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Posted 30 March 2009 - 10:12 PM

Hi Don,

Yes, it depends on your location. Here's a website that will look up your latitude and longitude based on your zipcode and then look up the magnetic declination. If, for example, your declination is 5 degrees west, your compass needle points 5 degrees west of true north.

#3 Lane

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Posted 30 March 2009 - 10:13 PM

You do need to know your location then it is just a simple process of adding or subtracting degrees from the magnetic north position on your compass. The degrees to add or subtract can be found on a topographical map of your area like the kind you buy at REI for hiking. It isn't a very orderly pattern either, the magnetic lines curve all over the place. I am sure you can find the info someplace on the web also.

#4 Lane

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Posted 30 March 2009 - 10:16 PM

Oops - I see Don already found you a web site.

#5 donnie3

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Posted 30 March 2009 - 10:31 PM

thanks very much, appreciate. don

#6 dpastern

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Posted 30 March 2009 - 10:45 PM

One more (accurate) way imho of doing this is location solar noon. Check this site out:

http://www.srrb.noaa...se/sunrise.html

Enter in your latitude/longitude and the date. It will tell you when solar noon is. Have a nice stick in the ground, ready for it. Mark it at the appropriate time. Done.

Dave

#7 Unknownastron

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Posted 30 March 2009 - 11:22 PM

Registering at the CalSky website and inputing accurate location from a map will also give your magnetic offset. Note that it changes slightly year to year but much less than a degree.

#8 Chris Rowland

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Posted 31 March 2009 - 06:41 AM

I looked up the culmination of the Sun in CdC and used the shadow of a plumb line at that time.

I'm beginning to think that every astronomers garden needs an accurate N/S line set up permanently :-)

Chris

#9 Miguel Lopes

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Posted 31 March 2009 - 07:39 AM

If you are near a large mountain with iron core or something similar, the compass is useless.

First you need to clarify if you want to find the magnetic north or the earth rotation north. They are very different in some parts of the globe.






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