 |
How does a compass know which way north is? |
Today a lot of people have GPS (Global Positioning System) devices that receive signals from satellites that orbit the earth and tell people where they are. Compasses are nowhere near that complicated. They have actually been around for thousands of years, and the technology behind them has not changed very much at all in that time.
No matter which way you spin, a compass needle will always point north. It knows where to point because the needle is a magnet. Magnets are pulled toward other magnets, and there is a huge magnet that is pulling the compass needle. The huge magnet is the Earth!
Earth has a North and South Pole that are magnetic. We don’t really feel their pull because we’re pretty big, compared to a compass needle. Also, we’re not magnets. Each of Earth’s poles pulls on one end of the compass needle, causing it to point in a direction that shows us where north is.
Geographic North and Magnetic North
When we think of the North Pole, we usually think of the northern point on the planet where the Earth’s axis meets the surface of the Earth, but that is not where a compass needle points. There is a separate north pole for Earth’s magnetic field. This Magnetic North is actually located above Canada. Compass needles point toward it.
Normally we are far enough away from both North Poles that it does not matter if our compass needles point at one or the other. It might get tricky though if you are in Northern Canada and trying to get to the Geographic North Pole though, because your compass needle will be pointing the wrong way!
Finding North Without a Compass
There are actually many ways to find where north is if you don’t have a compass handy. This one works at night (and probably best on a clear night.)
Can you find the Big Dipper in the sky? You’ll see its long handle and then the cup part that does the scooping. Four stars make up the cup. The two stars farthest away from the handle are actually very useful. They can point you to the North Star. Start with the one at the bottom of the Big Dipper and then follow an imaginary line through the second star, and keep the line going. Pretty soon, you’ll run into a very bright star: the North Star.
What’s so special about this star? It is pretty much directly over the North Pole, so if you can find it, you know which way north is! The next time you see the Big Dipper in the sky, see if you can use it to find the North Star.
