The Earth’s Magnetic Field
A compass needle points north because of the Earth’s magnetic field. The Earth acts like a giant magnet with invisible magnetic field lines surrounding it. These field lines emerge out of the ground at the south magnetic pole and curve up and over the Earth, entering the ground again at the north magnetic pole.
The Earth’s core is made up of molten iron and nickel, which moves in a fluid motion. This motion generates an electric current which produces the magnetic field through a process called the geodynamo effect. So in essence, the Earth’s core acts like a giant bar magnet, creating the magnetic field that encompasses the planet.
How Compass Needles Align to the Magnetic Field
A compass contains a tiny magnetized needle that has a north pole and a south pole. The north pole of the compass needle aligns with the Earth’s magnetic field lines, pointing toward the south magnetic pole near the geographic north pole. That’s why the north end of the compass needle points north – it’s attracted to the Earth’s south magnetic pole.
Compass needles align to the magnetic field lines in the area they are located. The closer you get to the north magnetic pole, the more vertical the magnetic field lines become. At the magnetic poles themselves, the magnetic field lines are perpendicular to the Earth’s surface.
Variation from True North
The direction a compass needle points is called magnetic north. This is different from true north, or the direction of the geographic North Pole.
The difference between true north and magnetic north is called declination. Declination varies depending on your location on the Earth.
This is because the magnetic poles are not stationary – they slowly drift over time. Currently, the north magnetic pole is located in northern Canada, hundreds of miles away from the geographic North Pole.
Disturbances to the Magnetic Field
The Earth’s magnetic field can be disturbed by solar activity like solar flares and sunspots. This can cause the phenomenon known as a magnetic storm. During a magnetic storm, compass needles can be deflected significantly from magnetic north.
The orientation of the magnetic field lines is also different at different latitudes. Nearer to the north and south magnetic poles the field lines are almost vertical, while near the equator they become more horizontal. This also impacts the accuracy of compass needles in some locations.
The Importance of Understanding Variation
It’s important for navigators to understand that a compass needle points to magnetic north, not true north. Variation needs to be accounted for when using a compass for navigation. Topographic and nautical maps will note the declination for the area to allow proper orientation between magnetic and true north.
So in summary, a compass needle aligns with the Earth’s invisible magnetic field lines, pointing toward the ever-shifting magnetic poles – which is why it points north.