Tag Archives: compass

Prepper Life Skill: Finding North Direction

10 Sep

Finding North is a skill many urban preppers will never need. But, it’s good to learn.

If you have a compass and you know your area’s magnetic declination, you can find true north easily. Your compass will point to magnetic north (which changes slightly with time. In the 1970s, it was about 6 degrees easterly declination down the center of Minnesota. Now, it’s less, because of westward movement of the isogonic lines.)

If you have a map, it will give a little picture showing declination. Even if you don’t have a map, it’s good to know the approximate declination in any wilderness area you frequent. NOAA has a nice declination map you can zoom in on.

Declination is the angle between True North (The North Pole, approximately the North Star) and magnetic north. Declination (measured in degrees) is a measurement of how much true north differs from magnetic north. Easterly declination means magnetic north is east of true north. On a map with north at the top, magnetic north will be to the right of true north (for easterly declination).

The way I remembered it (not saying this is proper!) is that the line from the Great Lakes down to Florida was the line of zero declination. Think of the magnet as being there, along that line. If you’re to the west of that line, declination is easterly. If you’re to the east of that line, declination is westerly.

If straight ahead is north and you’re west of the zero declination line, magnetic north must be east of you. The magnet is off to your right on the map. The compass points right to the magnet. Declination is easterly.

Here’s a really wonderful explanation of how to use a compass by crawlingroad on Youtube (3 parts):


http://www.youtube.com/watch?v=RZACnu2Ik-I


http://www.youtube.com/watch?v=d7pPYm0Q-GQ


http://www.youtube.com/watch?v=oN2NxjKQ1FQ

He discusses magnetic deviation and errors that can occur due to local magnetic fields in Part 2. That’s really important. Inside a house, I can get a compass to point in just about any direction by walking around close to walls. As Bradford Angier wrote in the 1970s, the only house you can trust a compass inside is an Igloo!

For those learning land navigation, it’s good to choose a compass with an adjustment for declination. One important reason is that your compass has an orienting needle in addition to the magnetic needle. If your compass doesn’t have an adjustment for declination, you’re left with two bad choices. Because the orienting arrow always points North, you must either orient your compass by trying to get the magnetic needle to point to six degrees or whatever. It’s much easier to get the magnetic needle lined up inside the orienting arrow. But, to make use of the orienting arrow, your compass card sits askew, with it saying true north isn’t where it is. The third option you have is doing math in your head.

With the adjustment for declination, you can free the compass card and the cardinal directions N, S, E, W from that silly orienting arrow. What this means is that you line up the magnetic arrow with the orienting arrow (set for declination) and the compass card will show you north immediately. The compass card will be aligned correctly.

Nothing is ever easy. I was going to recommend good old Silva of Sweden compasses, but apparently some other company owns the name in the US and sells Chinese and other compasses under that name. (The last compass I purchased was decades ago). The compass the guy shows in the video looks great. It’s the Suunto M-3G. Don’t know where it’s made, but I want one!

One thing I noticed immediately about the compass was its rounded back where it is held in the hand. I have an older Silva one that has a square, clear base. When holding it in the hand for a while that crummy corner cuts into your palm.

Another way to find true north is to use the North Star, Polaris. This is most easily found using the cup of the Big Dipper as a pointer. Polaris is within 2 degrees or true North. Some travelers use the North Star to confirm their compass’s declination.

Here are some links to help you learn just enough astronomy to find the Big Dipper and the North Star:
http://www.dustbunny.com/afk/constellations/bigdipper/

http://skywatchingworld.com/finding-big-dipper-constellation/
(Nice shot of sky)

http://www.physics.ucla.edu/~huffman/finddip.html
(Info about finding the north star and big dipper)

The final method I’ll mention is using a sun compass. You need a string, a straight rod, a sinker (to use as a plumb bob), and some rocks or sticks. Because the sun rises in the east (more or less) and sets in the west (more or less), we can use the movement of the sun to estimate North.

Place the rod in the ground and use the sinker and string to assure the rod is pointing straight up and isn’t canted. Tie the string around the rod at the bottom and follow the string to the end of the rod’s shadow. Tie a twig to the string at that point. Mark where the shadow is (with a rock or another twig) and then trace out a circle the string’s distance away from the rod.

At a later time, the shadow will again touch the circle. Mark that point. (Do this before noon. The shadow will be shortest at noon.) Draw a line between the two points on the circle. A line perpendicular to that will be North-South.

In the Northern latitudes, the shadows will point to the North. Oppose in Southern Hemisphere below 23.5 degrees latitude. This 23.5 degrees allows for the earth’s tilt. In the Northern areas, another way to think about this is to draw two lines from the rod to the two points where the shadow meets the circle. It will look like a mouth, like in the Game Pac-Man. The mouth points to the North.

You can determine North  another way by remembering that the sun is moving westward. Treating yourself as a compass, pointing north, your back to the south, your right arm is to the east and your left is to the west. By knowing which way is generally west, the movement of the sun tells you which way is north along the north-south line.

One thing that confuses some: You’ll see the shadow moving. So, that must mean the shadow is moving to the west? Correct? Or not? Try this: Use two flashlights. Use one as the stick in the ground. Use the other as the sun. Move the flashlight in one way to as if it were the sun, observe which way the shadow moves.

Here’s a really nice video about using the sun compass (from colhane). Warning: He is in the Southern Hemisphere, which changes the orientation of the shadows. There the shadows point not to the north, but to the south, so the Pac-Man mouth doesn’t work.


http://www.youtube.com/watch?v=zWueOSLpbbw

Natural Compass: Shadow Stick Method:


http://www.youtube.com/watch?v=MwuY0YBTeo0
(from ryanjcus)

This site has a summary of the sun compass method.

Backpackers today still know how to use compasses, but the GPS is becoming the land navigational tool of choice. If you travel into woods, I’d recommend learning how to use a compass, but I’d also carry a GPS. And, learn to find the North Star.

I searched for some Internet commentary to discuss the errors in the sun compass and the watch compass and found this.

Here’s a link to Field Manual MAP READING AND LAND
NAVIGATION (pdf). This has some good stuff, but I prefer the civilian books that aim to teach campers. Every serious prepper should get one good book about land navigation and study it.

Charlie P., author, The Prepper Next Door: A Practical Guide For Disaster And Emergency Planning.

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