Hemispheres, parallels and meridians
The Earth is shaped like a ball, called a sphere. To find places on it, geographers draw imaginary lines on maps and globes. You cannot see them on the real Earth, but they are very useful!
The Equator and the two hemispheres
The Equator is an imaginary line around the middle of the Earth. It cuts the planet into two halves called hemispheres (hemi means half).
The half between the Equator and the North Pole. Spain and all of Europe are here.
The half between the Equator and the South Pole. Australia, Argentina and Antarctica are here.
Parallels and meridians
Circles that go around the Earth from east to west, parallel to the Equator. The Equator is the biggest one. Two famous parallels are the Tropic of Cancer and the Tropic of Capricorn.
Half circles that go from the North Pole to the South Pole. The most important one is the Greenwich Meridian (the Prime Meridian). It divides the Earth into the Eastern and Western Hemispheres.
The Greenwich Meridian crosses Spain! It goes through Aragón and the Comunidad Valenciana, near Castellón. So part of Spain is in the Eastern Hemisphere and part is in the Western Hemisphere, but all of Spain is in the Northern Hemisphere.