How to determine true south?

   / How to determine true south? #1  

stumpfield

Gold Member
Joined
Dec 7, 2005
Messages
455
Location
Sierra Foothills
Tractor
2005 MT265B
Anyone know a practical method to determine true south without hiring a surveyor? I tried using a compass to find magnetic south then compensate for my latitude but having a hard time getting consistent readings. Each time I tried, I got a slightly different reading. May be I need a better compass or more steady hands???? ...trying to mount my solar panels in the most optimun position. Thanks for your help.
 
   / How to determine true south? #2  
Stumpfield,
You will need a plumb bob and the NOAA website to determine what time Solar Noon is.

Hang the plumb bob and at precisely Solar Noon trace the Plumb Bob line shadow on a horizontal surface and that will be True North/South.

NOAA has a Sunrise/Sunset calculator that will tell you the time of Solar Noon. Go to the main page and type calculator in the search bar. should bring it up for you.

Good luck :)
 
   / How to determine true south? #3  
First, go to: http://www.ngdc.noaa.gov/seg/geomag/jsp/Declination.jsp to get your magnetic declination. That's the angle between mag north & true north for your place on the globe. For Mariposa, CA the declination is 14 Deg., 13 min. E, which means your compass points 14 deg. east of true north.

Then subtract (or maybe it's add? I always have to think about this) the declination from what your compass says is north, i.e., if the declination is 14 degrees for your location, subtract 14 from 360 and that will be true north for your location; subtract 14 from 180 & you get 166, which should be true south. Confirm by sighting down a property line with a fence line running N-S, which should be very close. If you hsould have added, it will be off by almost 30 degrees.
 
   / How to determine true south? #4  
I have two compasses with declination adjustment. One was about $15 in a sporting goods store, the other is a Silva brand and was about $50 at REI.

Both are adjustable for declination, although the Sliva is both easier to adjust and more accurately adjustable.

Either one will get me within 1 degree of North or South. This is far better than you need for the solar panel. You will lose about 0.015% efficiency if you are one degree off on pointing it. If you are off by 5 degrees you will lose 0.4%.

The Silva compass also has an inclinometer, which I find useful for estimating the height of a tree. If I find the point where the top of the tree is 45 degrees from horizontal, the distance to the base of the tree, plus the height of my eye, is the height of the tree.
 
   / How to determine true south? #5  
Hey stumpfield try this pdf. It has been helpful for me. It's a couple pages of how to site your solar panels.
 

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   / How to determine true south? #6  
Oh! THAT true south. I thought you were talkin' Rebel flags, Grits, and Y'all come back now, he'ya.;)
 
   / How to determine true south? #7  
Take a stick, poke one end in the ground and point the other directly at the sun. If you do this right there'll be no shadow. Go away for awhile. When you come back the shadow points due east. South is a 90 degree right turn from there.
 
   / How to determine true south? #8  
Go to the North Pole and every direction will be south. Very simple.
 
   / How to determine true south? #9  
Site that may help for declination; http://http://www.thecompassstore.com/decvar.html

Site that may help determine true time also refered to as sidereal time. http://http://www.jgiesen.de/SiderealTimeClock/index.html

Between those two you should be in fine shape.

As the noth was mentioned you can locate the North Star at night and get a good north south orientation set up. It may be a little inaccurate because of pressession of the earths axsis but this amount will be to small to effect the instruments you will be using.

Have fun:D
 
   / How to determine true south? #10  
Egon said:
Site that may help for declination; http://http://www.thecompassstore.com/decvar.html

Site that may help determine true time also refered to as sidereal time. http://http://www.jgiesen.de/SiderealTimeClock/index.html

Between those two you should be in fine shape.

As the noth was mentioned you can locate the North Star at night and get a good north south orientation set up. It may be a little inaccurate because of pressession of the earths axsis but this amount will be to small to effect the instruments you will be using.

Have fun:D

Yep, two stakes on a clear night will get you a very accurate N/S line. About the simplest of all the suggestions.

Harry K
 

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