Finding Points On A Globe
Now that we understand the shape and size of our planet, let's consider the difficult challenge of measuring and describing points thereon. How, for example, do we tell someone who lives on the other side of the Earth where another object is located? Suppose that we are in an unfamiliar land and we need to find a distant but important object that is hidden somewhere else on the Earth. If we just start walking in a random direction, are we likely to find the hidden object?
In order to both study and navigate the Earth, it is important to have a system for describing locations accurately and mathematically. This system must be generally accepted by everyone, and it must be easy to use and understand.
The simplest method for describing locations either on a planet, or on any flat object, is to create a grid. A grid is a series of evenly spaced imaginary lines that intersect with one another at right angles. One set of lines are distributed across the globe horizontally, and one set of lines are distributed vertically.
But wait a moment. How do we know where the top and bottom of the Earth are? Think about it. If the Earth is round, what point is the top? Let's consider a white marble. Where is the top of the marble? No matter which way you turn it, every side of the marble looks the same. But what happens when you spin the marble? As the marble spins, or rotates, for a few moments, there is a clearly defined top that remains pointing upwards.
Because the Earth is rotating around an imaginary axis, we can define a top and bottom. We call these the poles. Having a top and bottom of the Earth allows us to then draw the imaginary lines that we need for our grid. The lines that extend from pole to pole are called longitude, while the lines that circle the globe horizontally are referred to as latitude.