A hemisphere is exactly half of a sphere, like cutting a perfectly round ball down the middle. The word comes from Greek roots meaning “half” and “sphere.”

When geographers talk about hemispheres, they're usually dividing Earth into halves. The Northern Hemisphere includes everything north of the equator: Canada, Europe, most of Asia, and the northern parts of Africa and South America. The Southern Hemisphere contains everything south of the equator: Australia, Antarctica, most of South America, and southern Africa.

Earth can also be divided into Eastern and Western Hemispheres, though geographers disagree somewhat on exactly where to draw that line. The hemisphere you live in affects your daily life more than you might realize. When it's summer in the Northern Hemisphere, it's winter in the Southern Hemisphere. If you live in the Northern Hemisphere and look at the night sky, you'll never see the Southern Cross constellation, which is only visible from the Southern Hemisphere.

Scientists also use the word to describe half of your brain. Your left hemisphere mainly controls the right side of your body and is important for language, while your right hemisphere mainly controls the left side and helps with spatial reasoning and creativity.