The Southern Hemisphere is the part of Earth that lies south of the equator. The word hemisphere (from the Greek word σφαιρα (sphere) +ημι (half)) literally means 'half ball' or "half sphere". It is also that half of the celestial sphere south of the celestial equator.

The Southern Hemisphere contains all or parts of four continents (Antarctica, Australia, most parts of South America and southern half of Africa), four oceans (South Atlantic, Indian, South Pacific, and Southern) and most of Oceania. Several islands off the Asian continental mainland are also in the Southern Hemisphere. Due to the tilt of Earth's rotation relative to the Sun and the ecliptic plane, summer is December to March and winter is June to September. September 22 or 23 is the vernal equinox and March 20 or 21 is the autumnal equinox.