How to Find True North


Cartography conventions help people make sense of a map immediately, which makes it easier to find their way.
Cartography conventions help people make sense of a map immediately, which makes it easier to find their way.

Suppose you decide to make a trek to the North Pole. You can't catch a plane there. So instead, you pull out your compass, watch the needle swing northward and plot a path, right? Wrong. To get to the North Pole, or true north, just following your compass needle won't work.

If you want to get from a point at the bottom of a map to one at the top, you need to head true north. True north is a geographical direction represented on maps and globes by lines of longitude. Each line of longitude begins and ends at the Earth's poles and represents direct north and south travel.

Compasses, on the other hand, direct you to magnetic north, a point in the arctic regions of Canada that continually shifts location based on the activity of the Earth's magnetic fields. Fluid iron in the planet's core acts like a huge bar magnet, creating a relatively weak magnetic field. The force of that magnetic field has a horizontal component in the direction of magnetic north. A compass needle is magnetized and freely suspended to allow that horizontal force to pull it toward magnetic north as well.

But the Earth's magnet isn't perfectly aligned with the geographical poles. For that reason, there is a difference between true north on a map and the north indicated by your compass. That difference is called the magnetic declination and is measured by the angle between true north and magnetic north when plotted on a map.

Magnetic declinations vary from place to place, depending on the intensity of the Earth's magnetic fields. For instance, if you hold out a compass in New Zealand, magnetic north will be about 20 degrees east of true north, whereas the declination in Los Angeles is 12 degrees. Geographical lines do exist where true north and magnetic north are aligned, and these are called agonic lines. In North America, one currently runs through the panhandle of Florida up to the Great Lakes and into the Arctic Ocean.

Given these irregularities, how will you ever reach the North Pole or a true north destination? Read on to find out how you can do it -- any time of day and with man-made and natural navigation tools.

Finding True North with Navigation Tools

Adjust your compass to find true north.
Adjust your compass to find true north.
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One of the simplest ways to find true north is with a Global Positioning System (GPS). A GPS recognizes your location by compiling the location information provided by multiple satellites that orbit the Earth. If you have one, you can select a 'true north' setting on your GPS, enter your destination, and it takes care of the rest.

Some cell phones are also equipped with compass capabilities. The Verizon Navigator, for example, comes with GPS hardware installed. These types of phones are becoming increasingly popular, particularly in Japan, where some models allow users to point them toward a destination, and the phone returns literally step-by-step directions. There are also free compass programs that you can download from the Internet to your phone. The compass will come into action when you point the phone in the direction of the sun. For a more traditional approach to navigation, let's look at the compass.

To find true north, you need to know your local declination value, or the angle difference between true north and magnetic north, discussed earlier. That information will either be listed in your map's legend or you can find it online at government Web sites, such as the National Geophysical Data Center. Why go to all this trouble? Even a 1 degree difference in true north and magnetic north can land you up to 920 feet (280 meters) off-course [source: Curtis].

You can adjust your compass to find true north.
Darryl Leniuk/Getty Images

There are a few options for adjusting your compass to true north. First, be sure to know whether the declination number is positive or negative, which is determined by whether you are east or west of the agonic line. If you are east of the line, it will be negative, meaning you turn the ring clockwise; west of it is positive, meaning you turn the ring counterclockwise.

Some compasses allow you to manually adjust the needle to compensate for the declination. Otherwise, you can use the bezel ring on a compass to set the magnetic declination by turning the ring until the orienting arrow points to your declination value. Then, hold the compass in your hand. When the needle and orienting arrow line up, the direction of travel arrow on the base will point true north. You can also accomplish this by aligning the orienting arrow and the direction of travel arrow. Then, hold out your compass and turn your body until the needle points to your declination. The orienting arrow and direction of travel arrow indicate true north.

Next, we'll explore ways to find true north using our celestial compass, the sun.

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Finding True North with the Sun

You can use your watch to find true north.
You can use your watch to find true north.
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If you're lost during the day somewhere without a map, compass or GPS handy, the best method to find your direction is to look up. The movement of the sun can illuminate your way true north. But to use this solar guide, you'll need to remember a few important things. In the Northern Hemisphere, the sun always rises in the east and sets in the west. At noon, it looms in the middle of the horizon and directly south. That means when you're facing the sun at noon, walking directly toward it will take you south. Walking with the sun at your back means you're heading north. The opposite is true in the Southern Hemisphere.

If it isn't noon, and you want to find your directions during daylight, an analogue watch with minute and hour hands can serve as a substitute compass. First, make sure the watch displays the correct time. Then, point the hour hand at the sun. Next, holding the watch in place, imagine an angle formed by the hour hand and a line from the 12 o'clock position to the center of the watch. Then draw an imaginary line bisecting that angle. That line indicates south in the Northern Hemisphere. During daylight saving time, create the angle from the one o'clock position instead of the 12 o'clock position.

In the Southern Hemisphere, point the 12 at the sun, instead of the hour hand. Then, form an imaginary angle between the hour hand and a line from the 12 to the center of the watch. The line bisecting that angle represents north.

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Don't have a watch? No problem. As long as you know the correct time, you can draw out your own clock on a paper and use it the same way.

You can use a stick and the shadows from the sun to find approximate true north.
2008 HowStuffWorks

For another way to get your bearings, find a stick and a large sunny spot on the ground. For this approach, remember that when the sun casts shadows, those shadows are in the opposite direction as its position in the sky. That means when the sun is in the eastern sky, its shadows will point toward the west.

That said, grab a stick, preferably about a yard (1 meter) high, and stab it in the ground in a sunny area so that you can see its shadow. Use a rock or other sharp object and mark the tip of that shadow on the ground. Since the sun's shadows move from west to east during the day, this first point stands for west.

Catnap for 15 minutes or so, then mark where the stick's shadow has moved. Now you should have two spots in the dirt: The first spot represents the west and the second spot represents the east. If you draw a line between those two spots, you have a general idea of your east-west line. From there, you can draw your north-south line at a 90-degree angle to the east-west line.

­In the Northern Hemisphere, moss on the southern side of trees is usually greener.
Chris Cheadle/Getty Images

Although these aren't precise directional guides, there are other clues in nature to help orient you toward true north:

  • Moss on trees -- Although common convention holds that moss grows on the north side of trees, that isn't always the case. However, in the Northern Hemisphere, moss on the south side of trees will be thicker and greener because that side often gets more sun.
  • Trees -- The bark may be duller and branches more extended to the sky on the north side of trees because it doesn't receive as much sun.
  • Melting snow -- Snow may melt faster on the warmer southern side of rock faces or mountains.
  • Ant hills -- Ants often build their nests on the south or southeastern side of trees where it is warmer.

OK. So we know how to find true north in the daylight. But what about when it's dark? Read on to the next page to learn how to find true north by the moon and stars.

Finding True North with the Moon and Stars

At night in the Northern Hemisphere, the constellations can point you to true north.
At night in the Northern Hemisphere, the constellations can point you to true north.
2008 HowStuffWorks

Even though the sun sets at night, the moon and stars can also shine a light to the true north.

According to the Special Air Service Survival Guide, a waxing or waning moon can offer some general directions. If the moon rises before sunset, the bright side is in the west. If it rises after midnight, the eastern side is illuminated. Once you know one direction, it's easy to put together the rest.

To understand why this is, remember that we see the sun as moving from east to west in our horizon. We also know that the moon orbits the Earth, and the portion of it that we see depends on how the sun's light shines on it. When the moon is between the sun and the Earth, the moon appears invisible. But as the moon moves in its 28-day counterclockwise orbit, the waxing moon first becomes visible in the western sky around sunset; it is illuminated by the sun, which is in its western position. Then, when the moon begins to wane and its orbit has reached the opposite side of the Earth, it becomes visible after midnight. At that point, it is illuminated by the eastern sunlight.

If the moon isn't visible, you can also use the stars for direction. The stars have been helping explorers navigate for centuries. In the Northern Hemisphere, the North Star, or Polaris, guides you true north. You can find Polaris by first locating the Big Dipper and Little Dipper constellations. Draw an imaginary line from the two "pointer stars" at the base of the bowl of the Big Dipper to the last and brightest star in the handle of the Little Dipper. Polaris is also the middle star in the 'M'-shaped neighboring constellation, Cassiopeia.

In the Southern Hemisphere, the Southern Cross constellation points you to south.
2008 HowStuffWorks

The Southern Hemisphere doesn't have a comparable star to Polaris, but the Southern Cross constellation can provide a good approximation of where south lies. Locate the constellation and the two pointer stars at the tip of it, and then extend that line about five times its original length. At that point, drop down an imaginary perpendicular line to the earth, and that marks south.

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Sources

  • Air Land Sea Application Center. "Survival, Evasion and Recovery." U.S. Army. June 1999. (March 10, 2008). http://www.equipped.org/multiservice_ser_manual_1999.pdf
  • Boswell, John. "U.S. Armed Forces Survival Manual." Macmillan. 2004. (March 10, 2008) http://books.google.com/books?id=oouaSH91rqQC&pg=PA17&lpg=PA17&dq=survival+guide+true+north&source=web&ots=tCsMCDJUHx&sig=EQ8gQ1Wl4gk6hv1mtoHc6ZECC5g&hl=en#PPA26,M1
  • Cooper, Donald C., Nasar. "The Fundamentals of Search and Rescue." Jones & Bartlett Publishers. 2005. (March 10, 2008)http://books.google.com/books?id=JWNcKsY6DfMC&pg=PA76&dq=find+north+without+a+compass&lr=&sig=t-dwE9gHGog7ggUAt8bzJLx8MuQn
  • Curtis, Rick. "OA Guide to Map and Compass -- Part 2." The Backpacker's Field Manual. Random House. 1998. (March 10, 2008) http://www.princeton.edu/~oa/manual/mapcompass2.shtml
  • Geological Survey of Canada. "Geomagnetism: Magnetic declination." Updates Jan. 18, 2008. (March 10, 2008) http://gsc.nrcan.gc.ca/geomag/field/magdec_e.php
  • Hattingh, Garth. "Outdoor Survival." Stackpole Books. 2003. (March 10, 2008)http://books.google.com/books?id=uOVcjPotq_gC&pg=PT41&dq=find+north+without+a+compass&sig=kV5sP3TybX6DHBSJ7yTdEaMeRM4
  • Markoff, John and Fackler, Mark. "With a Cellphone as My Guide." The New York Times. June 8, 2006. (March 10, 2008) http://www.nytimes.com/2006/06/28/technology/28locate.html?pagewanted=1
  • Tawrell, Paul. "Camping & Wilderness Survival: The Ultimate Outdoors Book." Outdoor Life. 2006. (March 11, 2008) http://books.google.com/books?id=deRKF5kv5wwC
  • Tymony, Cy. "Sneaky Uses for Everyday Things." Andrews McMeel Publishing. 2003. (March 10, 2008) http://books.google.com/books?id=QZNmrOpkB6sC&pg=PA142&dq=find+north+without+a+compass&lr=&sig=SPXE04c6OevRCNMOrHlJ82iBTEk
  • United States Search and Rescue Task Force. "Compass Basics." (March 11, 2008) http://www.ussartf.org/compass_basics.htm
  • Wiseman, John. "SAS Survival Handbook." HarperCollins. 2004. (March 10, 2008) http://books.google.com/books?id=65-o2qppedcC&printsec=frontcover&sig=K5A3F2XCCYmekz98ercv1ksbZKo&source=gbs_similarbooks_r&cad=1_1#PPA347,M1