A circle drawn around Earth’s center divides it into two equal halves called hemispheres,
or half spheres. Though this can be done in infinite ways. However,
there are generally considered to be four hemispheres: Southern,
Northern, Eastern, and Western. To get the Western and Eastern
hemispheres, the intersection happens at the prime meridian. To get the Northern and Southern hemispheres, the intersection happens at the Equator.
The Equator, or line of 0 degrees latitude, divides Earth into the Northern and Southern Hemispheres. The Northern Hemisphere
contains North America, the northern part of South America, Europe, the
northern two-thirds of Africa, and most of Asia. The Southern
Hemisphere contains most of South America, one-third of Africa,
Australia, Antarctica, and some Asian islands.
There are differences in the climates
of the Northern and Southern Hemispheres because of Earth's seasonal
tilt toward and away from the sun. In the Northern Hemisphere, the
warmer summer months are from June through September. In the Southern Hemisphere, summer begins in December and ends in March.
Earth can also be divided into hemispheres along meridians, or lines of longitude. The prime meridian, or 0 degrees longitude, and the International Date Line, 180 degrees longitude, divide Earth into Eastern and Western Hemispheres.
Many geographers consider the 20 degree west line of longitude and the
160 degree east line of longitude as the Eastern and Western
Hemispheres. This calculation is made so that Africa and Europe are not
split.
The idea of Eastern and Western Hemispheres has become politically and historically significant since European nations began colonizing North America and South America. In this context, the Eastern Hemisphere is sometimes called the "Old World," and the Western Hemisphere is called the "New World."
However, the Western Hemisphere is a purely geographic term and should
not be confused with other mentions of the "Western" world, which is
often used to describe parts of Europe, North America, and other world
regions that share some economic, social, and cultural values.