Half a sphere is defined as a hemisphere. The term hemisphere is derived from the Greek word "hemi," which means "half" and the Latin word "shaera," meaning "globe."
Hemispheres are everywhere. The Earth is the common example of a hemisphere. As a cylindrical body, the Earth is sectioned into four separate hemispheres – North and South and East and West. The human brain is often broken down into the cerebral hemispheres.
The Earth’s hemispheres naturally divide into seasonal opposites. The Northern Hemisphere, due to the tilt toward the sun, experiences summer from June through September and the Southern Hemisphere is in summer from December through March.