Finding True South the Easy Way: Page 2 of 2

Beginner

Inside this Article

Magnetic Declination (2005)
Magnetic Declination (2005)
Many things can negatively affect the accuracy of a compass
Q: Which of the elements in this scene can negatively affect the accuracy of a compass? A: Lots of them.
Recognizing the Big and Little Dippers can help you identify Polaris, the North
Recognizing the Big and Little Dippers can help you identify Polaris, the North Star.
Aligning an array to true south by siting the North Star.
Aligning an array to true south by siting the North Star.
Magnetic Declination (2005)
Many things can negatively affect the accuracy of a compass
Recognizing the Big and Little Dippers can help you identify Polaris, the North
Aligning an array to true south by siting the North Star.

The Easy Way

You might be surprised to learn that the most accurate method of determining true north completely bypasses magnetic deviation, magnetic declination, and all that calculating—and eliminates the compass altogether.

Just look up in the sky on a clear night. In the northern hemisphere, you will see Polaris, the North Star, stationary in the sky. The North Star is always either exactly or just a few tenths of a degree from true north. So all you need to do to face your system south is line up its north/south axis with the North Star. How do you find it? Look north (use your compass and allow for magnetic declination). The North Star is not the brightest star in the sky, but it is the brightest in that part of the sky. If you know what the Big Dipper looks like (take a look at Alaska’s state flag), follow the two pointer stars on the outside of the Big Dipper’s cup to find the North Star.

Case in Point

Before my partner Michele and I built our house, we had the solar-electric system installed so we could use solar energy for most of the home’s construction. After the modules were installed, I went out on a clear night to check the array’s orientation. Sure enough, the PV array had been installed about 15 degrees off true south. So I loosened the bolts and swung the array until the North Star lined up with the space between the left and right halves of the array. After retightening the bolts, the array was positioned to harvest 100 percent, not 98 percent, of the sun’s power.

I also used a similar method before our home’s foundation was laid. On a clear night, I went out to the site, pounded a tall fence post into the ground, and walked south-ish about 50 feet. Then I squatted down and moved a little until I lined up the North Star with the top of the fence post, and set a second post at this location. After double-checking the alignment, I had a positive reference for a true north–south line. I didn’t need to use any calculations, and I didn’t worry about magnetic deviation from iron ore, steel posts, or my cell phone. My contractor simply used the two reference posts to properly orient our passive solar house to true south.

Finding true north is easy, so why make it harder than it needs to be? And once you know true north, since true south is off by 180 degrees, you know it too—just turn around. Next time you need to do the important task of orienting a building or solar panels to true south, simply wait for a clear night and let the North Star be your guide.

Access

Grey Chisholm, PO Box 396, San Antonito, NM 87047 • 505-379-4173

NOAA • www.ngdc.noaa.gov/seg/geomag/jsp/Declination.jsp • Magnetic declination calculator

U.S. Geological Survey’s National Geomagnetism Program • http://geomag.usgs.gov

Comments (2)

Grey Chisholm_2's picture

Good Morning Mike Reed,

Yes, I like the daytime methods also. For true local apparent noon, all you have to do is calculate the time of local apparent noon. For a sailor like myself, with an almanac in hand, a piece of cake. For the highest arc, it takes at least a day to mark the sun's shadow. But once figured out, True South does not change. Both methods work well. Both methods are also written about in many sources. I like the Polaris method because you do not need to calculate anything, you do not need to mark shaddows over a time period. Polaris is just there. The disadvantage to Polaris is first, you have to be able to identify the star; and second, Polaris is not very bright so city lights or even a full moon can wash it out. But, on a clear dark night, it is the simplest method around.

Again, thank you for your words,

Fair winds,
Capt Grey Chisholm

solarmike's picture

Grey,

I've always liked the Polaris - night Sky approach.

For daytime applications it is easy to find "Solar Noon". At Solar Noon, a shadow cast by a vertical pole will point either directly north or directly south, depending on the observer's latitude and the time of year. At Solar Noon the Sun is at the "highest point" in the sky for that day and when measured in time, it is halfway between Sunrise and Sunset.

A nice calculator is found here: http://www.esrl.noaa.gov/gmd/grad/s...

Enjoy,

Mike Reed

Show or Hide All Comments

Advertisement

X
You may login with either your assigned username or your e-mail address.
The password field is case sensitive.
Loading