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Latitude and Longitude
demonstrate an understanding of the terms: equator, tropics, latitude, longitude, pole, horizon, meridian and zenith
We can say where a place on Earth is by giving its latitude and its longitude. With these two numbers
we can pinpoint any location on the surface of the Earth.
Latitude
The latitude of a location is how many degrees above (N) or below (S) of the equator it is.
The equator (the circle around the Earth the same distance from each pole) is at latitude 0, the North
pole at latitude 900 and places between are at a latitude between 0 and 90 N.
How can you find out your latitude experimentally?
Imagine you were at the North pole. The pole star would be directly above your head (at the zenith).
If you then walked south it would be lower in the sky the further south you went. In fact by measuring
its altitude (the angle it makes with the horizon) this will give you your own latitude.
In Middlesbrough the pole star is 550 above the horizon. One way that sailors could figure out how far
north they are is by measuring the position of the pole star. This can be done using an instrument
called an astrolabe. You could make your own using a protractor, a pen tube, some string and a
weight.
Describe how you would go about using the instrument above to find your latitude.
Where would the pole star be if you were at a point on the equator?
How do people in the southern hemisphere find which way is south?
Longitude
The longitude of a location is how many degrees east or west of the prime meridian it is.
Imagine lots of vertical circles on the surface of the Earth. A circle like this which goes through both
poles is called a meridian.
The equator is a natural zero for latitude but the zero for longitude could be anywhere. Greenwich in
London was internationally agreed. The line that goes through Greenwich is called the prime
meridian. Other places on Earth have longitudes between 0 and 180 E or W of this. E.g. if you
started at Greenwich and walked East 13 degrees you would end on a meridian which goes through
Berlin in Germany.
Why was Greenwich chosen as the international meridian?
pic Ian Britton - Freefoto.com
You cannot get your longitude just by observing the stars. We shall see later that you can work out
your longitude if you know the difference between what time it is where you are and what time it is in
Greenwich.
For a sailor to know accurately what time it is in Greenwich he will need an accurate clock. Various
astronomical methods were suggested (including observing Jupiter's moons which orbit Jupiter in a
predictable way) but the problem was eventually solved by John Harrison who invented a very reliable
watch.
Does the sun rise sooner or later in France than in England? Why?
Why would it be difficult for sailors to observe the moons of Jupiter?
Find a picture of John Harrison and his watch H4.
There is an excellent film called Longitude which tells the story of his work. Get it. There are a few
good clips on YouTube.
What capital cities can be found at the following? (you need a map of the world or you could use
Google Earth)
Latitude
52 N
23 N
22 N
34 S
33 S
Longitude
5E
82 W
114 E
151 E
71 W
City