Where are North and South poles?

 By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

14 November 2010

Writing from Kampala, Uganda, Henry Nyakoojo notes that “when one holds a compass anywhere on the surface of the earth it is supposed to point North. Can you take us through what happens as one moves from the equator in East Africa Northwards and ultimately stands at the North Pole? And the reverse journey to the South Pole? What is the situation when one is at the point known as True North with our compass?”

Before answering Henry’s question, let me point out something about what we call “North”. It is well known that like poles of a magnet repel one another while unlike poles attract.

Thus if you have a bar of magnet and you didn’t know which pole is which, you’d use a compass and the side that attracts the North Pole would be the South of the bar.

In the same way, it can be argued that the direction where the North Pole of a compass points is the South of the Earth. Therefore the continent of Europe, for example, is to the South of Kenya (and Uganda)!

Back to the original question: the magnetic compass points North (and South) because it aligns itself with the Earth’s magnetic field. Now if you picture the planet as a globe, the (imaginary) lines of this field will run from the South Pole to the North Pole.

At the North Pole, the field lines run into the ground, then continue through the Earth’s crust and emerge at the South Pole.

Thus if you stand at the Earth’s (magnetic) North Pole, the compass needle will align itself with the field there. That is; it will point downwards. When you think about it, this is exactly what you should expect. After all, the compass shows the direction of the North Pole, and that’s where you are standing, thus it points towards your feet!

Conversely, when standing at the South Pole, the compass will point upwards. Now that would be quite confusing because the North Pole is not located in the sky.

Henry also brings out the fact that there are two sets of poles: the magnetic North-South and the true North-South. The magnetic poles are the locations where the compass points directly vertically.

The true poles are the points where the axis of rotation of the planet passes through. If you look up from here, you will see the stars going round in concentric circles in the sky. The common centre of these circles marks the location of the poles.

The magnetic poles are not stationary at a fixed point. They move gradually at the rate of about 10km to 40km every year. At present, the North Magnetic Pole is located about 5 degrees from the true north. This is over 500km away – farther than the distance from Nairobi to Mombasa!