Antarctica and Australia are the two continents generally considered entirely within the Southern Hemisphere. The Southern Hemisphere is the half of Earth south of the Equator, extending from zero degrees latitude to the South Pole at 90 degrees south. Antarctica lies entirely south of the Equator and is centred around the South Pole. Australia is also entirely south of the Equator, with its northernmost mainland regions lying at roughly 10 to 11 degrees south latitude. The broader region of Oceania contains numerous islands both north and south of the Equator, but the Australian continent itself remains wholly in the Southern Hemisphere.
Antarctica is the most obvious example because the entire continent surrounds the South Pole and lies south of the Antarctic Circle except for small geographical complications involving islands and definitions of continental boundaries. The South Pole itself is located within Antarctica at 90 degrees south. Antarctica has no portion extending into the Northern Hemisphere. Its geographical position produces distinctive seasonal patterns, including polar day and polar night. At the geographic South Pole, the Sun remains above the horizon for approximately half the year and below the horizon for approximately half the year, although atmospheric refraction modifies the precise duration of visible sunlight.
Australia is also entirely south of the Equator. Its northernmost mainland areas lie in the tropical zone but remain several degrees south of zero latitude. The country therefore contains tropical, subtropical, temperate, desert and alpine environments without crossing into the Northern Hemisphere. The Australian mainland and Tasmania are both south of the Equator. Some Australian external territories can complicate political rather than continental classifications, because Australia administers territories located in different parts of the world. Such territories should not be confused with the geographical continent of Australia when answering the hemispheric question.
South America is not entirely in the Southern Hemisphere because the Equator crosses its northern part. The same applies to Africa and Asia, which are crossed by the Equator. Europe and North America are not entirely Southern Hemisphere continents because their principal landmasses lie north of the Equator. Antarctica and Australia are therefore distinctive among the standard continents because no part of their continental landmass crosses the Equator. This distinction is based on geographical latitude rather than climate. Both Australia and Antarctica occupy broad ranges of Southern Hemisphere climates despite their very different environmental conditions.
Hemisphere classification is based on latitude, not on compass direction or temperature. A location can be in the Southern Hemisphere while being very close to the Equator and therefore tropical. Northern Australia provides a clear example, because it is entirely south of the Equator but contains tropical climates with high temperatures and seasonal rainfall. Conversely, Antarctica is entirely Southern Hemisphere but is dominated by polar conditions. Therefore, being in the Southern Hemisphere does not mean being cold or having any particular climate. It simply means that the location lies south of the Equator.
The question becomes more complicated if continents are defined differently. Some geographical systems use Oceania rather than Australia as the continental name, and Oceania includes numerous islands north and south of the Equator. If Oceania is treated as a continent, it cannot be described as entirely Southern Hemisphere because countries and territories such as Kiribati, the Federated States of Micronesia and other Pacific islands extend into the Northern Hemisphere. Under the conventional seven continent model, however, Australia is the continent and is entirely south of the Equator.
Antarctica and Australia also differ greatly in their relationships with human settlement. Australia is a permanently inhabited continent with major cities, extensive agriculture, industry and diverse ecosystems. Antarctica has no permanent indigenous population and is primarily occupied temporarily by scientific and support personnel. Their common hemispheric position therefore tells us very little about their social or environmental similarity. The hemispheric classification is purely geographical. Australia contains tropical forests and coral reefs as well as deserts and temperate environments, while Antarctica is dominated by ice and polar ecosystems.
The standard answer is therefore Antarctica and Australia. Both lie completely south of the Equator, whereas the other conventional continents either cross the Equator or lie wholly north of it. The answer depends on using the conventional continental landmass classification rather than a broader regional definition such as Oceania. The key test is simple: a continent is entirely Southern Hemisphere if no part of its continental landmass reaches zero degrees latitude or extends north of the Equator. Antarctica and Australia satisfy that geographical condition.
