Which way is north?
By Luis J. Olivieri*
Imagine this: You are in a boat in the middle of the ocean without any visible landmarks. Everything from horizon to horizon is just water, all of which looks pretty much the same! You know that if you go west, you will get home in a couple of hours, but if you go east, you will be lost in the sea forever! We know that the Sun comes up in the east and sets in the west, but today, it's a cloudy day. How are you going to find your way home?" For centuries, sailors had exactly this problem. They had to rely on the Sun and the stars to navigate, but what happened on a cloudy day?
Over 2,000 years ago, the Chinese came up with a clever invention to solve this problem. They realized that if they put an iron needle on a floating material, such as a small piece of cork, and they floated this on water, the needle always ended up pointing in the same direction. Now, the big question is why does the needle always point in the same direction? Earth has a magnetic field that goes from the North Pole to the South Pole. The needle will align itself using this magnetic field. It doesn’t matter where you are on Earth. The needle will always point north.
There is something we have to take into consideration. The place where the Magnetic North is located is not really the North Pole, so the needle is not really pointing north. It points to the Magnetic North. The difference between the Magnetic North and the North Pole (known as True North) is called the magnetic declination and varies from place to place on Earth. In New Jersey, the difference is about 12°. Some compasses have the option to let you adjust for the magnetic declination. If someone tells you to head 90°, the first question you have to ask is if this is to the Magnetic North or the True North.
This simple piece of equipment with a needle always pointing to the Magnetic North is called a compass. The needle is usually in the shape of an arrow, with the top half in a red color. The needle is placed within a dial, also known as its housing, which sometimes is filled with various types of liquid (alcohol, kerosene, or another type of low viscosity oil) to make the needle more stable to movements. The dial is usually divided or numbered, clockwise around a circle from 0° (degrees) to 360°. North is always represented as 0° (also as 360°), East as 90°, South as 180°, and West as 270°. The direction you are heading in is called the "azimuth" or bearing, so if you have to head 180°, you have to go South.
You can have fun with a compass as many people do. There is a sport called orienteering where people use a compass, maps and instructions for finding points of places in a landscape. A standard orienteering course consists of a starting point and a series of control sites that are marked on a map. The person has to use a map, sometimes clues and a compass to visit each point and eventually get to the finish point.
*Luis Olivieri is the Senior Manager for the Geographic Information System Program.