The Equator, or line of 0 degrees latitude, divides the 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 the 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.
The 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 the 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.