Magnetism (6)

A compass needle points north–south because the Earth has a magnetic field. It is as if there were a giant magnet inside the Earth.

A compass points along the lines of the Earth’s magnetic field.

why the imaginary magnet inside the Earth is shown with a south pole at the top

The opposite poles of two magnets attract. Therefore, when the red end of a magnet or compass is pointing north, it is because it is being attracted in that direction by the south end of another magnet (often coloured blue) – this is the imaginary magnet inside the Earth.