The true north pole on Earth is the north point of the axis around which the Earth rotates. This axis is tilted about 23° in relation to Earth's orbit around the sun; that's what causes the seasons.
The axis currently points almost directly at a star called Polaris. Because it does, when you find it in the sky (in the northern hemisphere) you will be looking in a direction that is almost directly north. Using the north star as a guide, you can always tell which way is north.
Polaris has not always been the 'North Star', and won't be, in the future. The Earth spins on its axis just like a gyroscope, and 'precesses' as it spins ... the rotational axis slowly changes direction, in a circle, over thousands of years. Currently it points within one degree of Polaris. During the past 5000 years the axis has pointed at the star Thuban (Alpha Draconis); in the year 7500 the North Star will be Alpha Cephei; in the year 15,000 it will be the star Vega. About 9000 years after that, Polaris will again become the North Star.
You can also use the north star to determine your latitude on Earth. It's really simple ... the altitude of Polaris above the horizon, where you are in the northern hemisphere, is also your latitude above the equator. We'll show you why, below.
Have a look at the picture. Imagine you are standing at point Q.
The angle shown in the picture represents your latitude, in degrees, above the equator.
(For simplicity, Earth is shown here without its 23° tilt).
Now look at the diagram. You're still at point Q.
The horizon line is marked and everything you can see in the night sky is above this.
Now notice the two arrows pointing towards the north star. One is pointing towards Polaris from your position at Q. The other is the axis of the Earth, which also points at Polaris. (These lines are virtually parallel, even though they're pointing at a star, simply because the star Polaris is so far away).
Your latitude is shown by the angle 1.
The altitude of Polaris above your horizon is shown by angle 2.
A little geometry is used to prove that angle 1 and angle 2 are the same number of degrees.
Because the two arrows pointing at Polaris are parallel, there is a pair of corresponding equal angles (an 'F' pattern). These are angles 4 and 3. Angle 4 equals angle 3.
Angle DOX is 90° (because it's the angle between north and the equator).
Angle BQG is 90° (because it's the angle between your horizon and zenith).
Since Angle 4 equals angle 3, then the left-over portions of each 90° angle must also be equal: ie: angle 1 equals angle 2.
In other words, your latitude angle equals the altitude angle of Polaris above your horizon.
This means that wherever you are in the northern hemisphere, when you look up at the sky and find the north star Polaris, you'll know two things: which way is north, and your latitude.
Now let's look at what happens when you use a compass!
Earth has a second north pole. The Earth is a giant magnet; its magnetic field originates inside the Earth, in the outer core, and is produced by the movement of molten iron more than 3,000 km below the surface.
The Earth's magnetic field is shaped approximately like that of the bar magnet (shown at the right) and, like a magnet, it has two magnetic poles, one in the Canadian arctic and one off the coast of Antarctica.
Earth's magnetic north pole is where the magnetic field lines are oriented vertically, and plunge into the surface of the Earth. This location is near the true north (axis) pole, but not not right at it. It's about 960 km away.
Since compasses are attracted to the north magnetic pole, the needle on the compass isn't really pointing north at all ... just sort of north. It actually points slightly northwest.
Ordinarily this isn't a problem if you are using the compass to go a short distance; you'll never notice the error.
But all navigators, especially airplane pilots, have always known all about this problem, ... and it is a problem for them, as they regularly fly long distances, and the error that results from a compass not pointing at true north could put them hundreds of miles off course.
To solve this problem they use maps that show the declination angle ... the angle between magnetic and true north, for the spot they are at ... and correct their heading to account for the error. They also use a special compass that will make the correction for them.
It should be clear from the diagrams above that the farther north you go, the greater the declination angle, and the greater the error. This makes flying a plane in the arctic a little more difficult, as you always must adjust your heading for true north to make up for the compass error ... and the correction changes as you change locations! Special maps are available that show the declination angle for your current position.
However, pilots today don't have to rely on just a compass to find their direction. Global Positioning Satellites (G.P.S.) will report your exact location, and aren't affected by where the north magnetic pole is in relation to where you are.
Incidentally, when you're right at the north magnetic pole, where does your compass needle point? Well, it tries to point straight down ... but since it can't, it just spins in circles. There is in fact a special type of compass called a 'dip compass', where the needle is free to dip downwards. You can use it to measure how close you're getting to the north magnetic pole.
But there's more to the north magnetic pole. It's location isn't fixed in one spot ... it's moving! And quite quickly. The North Magnetic Pole is slowly drifting across the Canadian Arctic. In the last 50 years or so it has started to move faster; you can see on the map at the right how much it has moved since 1972, and where it was as recently as 2005.
Currently it is moving roughly northwest, at approximately 40 km per year. Scientists are constantly checking on its position, but because its location is now in the Arctic Ocean, they can only visit the location briefly each spring. The magnetic pole is drifting away from North America so fast that it could end up in Siberia within 50 years.
Because the magnetic pole is moving, maps showing the 'declination angle correction' quickly become outdated; new maps are prepared every so often to allow for the new position of the magnetic pole.
The reason the magnetic pole is moving is not well understood. It may have something to do with the movement of the molten outer core inside the planet due to convection currents within it, and the fact that its density is not uniform throughout. Wait ... there's more! The location of the pole is moving, but as it moves, it also wanders around! On any given day, it can be up to 80 km away from where you think it is. This wandering is due to disturbances in the Earth's magnetic field, perhaps caused by particles from the sun hitting the magnetic field lines. (These same particles cause the Northern Lights).
If the north magnetic pole does end up in Siberia in this century, Canada and Alaska could lose their northern lights!
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