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What is the prime meridian? |
The prime meridian is a name given to an imaginary line on the Earth. This line runs north-south through Greenwich, a borough of London, in England. It runs all the way from the North Pole to the South Pole.
What’s the point of having an imaginary line? The equator, which runs east-west, is another line like this. The north-south lines are called lines of longitude, and the east-west lines are lines of latitude. Each of these lines is numbered, and by knowing your longitude and latitude numbers, you can tell other people your exact position on a map. We can also use GPS (global positioning system or satellite tracking) to help us get to an exact location by entering in the longitude and latitude of a place.
The prime meridian’s longitude number is zero degrees (0°). Degrees doesn’t mean temperature here. It is a way to measure around a circle (the Earth.) The prime meridian is where the counting of longitude degrees begins. As you move east or west of the prime meridian your longitude gets higher and higher, until you are on the complete opposite side of the Earth, where your longitude will be 180°. That’s the highest longitude number possible.
There is no scientific reason why Greenwich was picked for the prime meridian. It was chosen by an international agreement in 1884 because it was the site of a well-known astronomical observatory.
Find Your Coordinates
If you have a GPS device, this will be pretty easy, but if you don’t, you can use a map. On most maps, there are numbers written along the edges telling you the degrees of latitude and longitude.
Find your home on the map and then trace a line straight up to the top of the map. If your finger lands between two numbers, you may have to guess what your longitude is. Now go back to your home and trace a line straight to the side of the map. The number there will be your latitude.
Your home is the only place on Earth with those exact coordinates (or numbers). What are the coordinates of some major cities in the world? How do those numbers compare to yours? Are they higher or lower? Does that mean a city is farther North? Farther West?
If you’re using a GPS device, you’ll get very exact numbers. They’ll probably look something like this:
38°37′31″N 90°11′0″W
You read that like this: “38 degrees, 37 minutes, 31 seconds north. 90 degrees, 11 minutes west. Minutes and seconds aren’t just for time. If you broke up a degree into 60 equal parts, one of those parts would be a minute. Just like on a clock, there are 60 equal seconds in a minute.
See if you can find those coordinates on a map. What’s there?
Just like your phone number or address, you should never give out your coordinates to strangers or people you do not trust.
