Hemispheres

Hemispheres are halves of a sphere. The term is used in geography, astronomy, anatomy, and other fields to describe two complementary halves of a rounded object or system.

On Earth, the most common use is to refer to the two halves divided by the equator: the Northern Hemisphere and the Southern Hemisphere. Another common division is by the prime meridian, producing the Eastern Hemisphere and the Western Hemisphere. In some contexts, four hemispheres are described by the two dividing lines, creating a conceptual grid for global reference. Boundaries are idealized circles or planes rather than exact physical separations, and practical definitions can vary by field or purpose.

Geographically, the Northern Hemisphere contains most of the landmass and human population, while the Southern Hemisphere contains a larger share of the planet’s ocean. These divisions influence climate, seasons, and daylight patterns, as well as navigation and regional perspectives. The equator is a precise geographic reference, whereas the meridians used to define the Eastern and Western Hemispheres have fixed longitudinal coordinates.

In anatomy, the brain is divided into two cerebral hemispheres, left and right. The hemispheres are connected by the corpus callosum and cooperate to perform most cognitive and motor functions. Each hemisphere tends to be more involved in certain processes, but most activities rely on integrated activity across both.

The term derives from Greek hemi- meaning half and sphaira meaning sphere. Hemispheres also appear in other sciences to describe half-spheres in celestial, planetary, or geological contexts.