A hemisphere is half of the Earth, and there are four of them. The Equator cuts the planet into the Northern and Southern Hemispheres. The Prime Meridian, a line running from the North Pole to the South Pole through Greenwich in London, together with the 180° line on the other side of the world, cuts it into the Eastern and Western Hemispheres. So every place on Earth is in two hemispheres at once. New York is in the Northern and Western. Sydney is in the Southern and Eastern. And one country, Kiribati in the Pacific Ocean, has islands in all four.
The word comes from Greek: hemi means “half” and a sphere is a ball. If you cut an orange through its middle, each piece is a hemisphere. Earth is just a very big orange that can be cut two different ways. Grab a globe, and let’s explore each line and half.
The Equator: a 40,075 km belt around Earth’s middle
The Equator is an imaginary line around the widest part of the Earth, exactly halfway between the North Pole and the South Pole. It is the line of 0° latitude. Latitude tells you how far north or south of the Equator you are, from 0° up to 90° at each pole. The Equator is about 40,075 km long. If you could drive a car along it at 100 km/h without stopping, the trip would take almost 17 days.
The name comes from Latin. Old scholars called it the “circle that makes day and night equal.” On the Equator, days and nights are close to 12 hours each all year long. Around 20 March and 23 September, on days called the equinoxes, the whole world gets nearly 12 hours of day and 12 hours of night.
Most of the Equator crosses water. About 31,361 km of it, or 78 per cent, runs over the sea, and only about 8,714 km crosses land. It passes over the land of 11 countries: São Tomé and Príncipe, Gabon, the Republic of the Congo, the Democratic Republic of the Congo, Uganda, Kenya and Somalia in Africa; Indonesia in Asia; and Ecuador, Colombia and Brazil in South America. Counting both land and sea, Indonesia has the longest stretch of the line. Here is a trick question to test your family: does Equatorial Guinea touch the Equator? No! It sits just north of the line, and only its small island of Annobón lies south of it.
Greenwich and the 1884 meeting in Washington that chose 0° longitude
The Equator was easy to find, because it is set by the way the Earth spins. The line from pole to pole that starts longitude was harder, because it could go anywhere. Longitude tells you how far east or west you are, from 0° up to 180°. For centuries, different countries used different starting lines. France measured from Paris, for example.
Sailors and railway companies found this very confusing. So in October 1884, the President of the United States, Chester A. Arthur, invited countries to a meeting called the International Meridian Conference in Washington, D.C. There were 41 delegates from 26 countries. They voted on which line should become the world’s zero. The result was 22 votes for Greenwich, 1 against (San Domingo, now the Dominican Republic), and 2 abstentions, from France and Brazil. France did not switch its official time to Greenwich until 1911, 27 years later!
The Greenwich line passes through the Royal Observatory in Greenwich, London. It was set up there in 1851 by the astronomer Sir George Airy. Visitors today line up to stand with one foot in the Eastern Hemisphere and one in the Western. At night, since 16 December 1999, a green laser beam has shone north from the observatory to mark the line in the sky. Here is a surprising fact: if you check your position with a phone’s GPS while standing on the metal strip, it shows you are not quite at 0°. Modern satellite systems put zero about 102 metres to the east.
After it leaves London, the Prime Meridian runs south through France, Spain, Algeria, Mali, Burkina Faso, Togo and Ghana before crossing the ocean to Antarctica. Where it meets the Equator, at 0° latitude and 0° longitude, there is only open sea, about 600 km south of the African coast in the Gulf of Guinea. Mapmakers jokingly call this spot “Null Island,” even though there is no island there at all.
The Northern Hemisphere, home to 87 out of every 100 people
The Northern Hemisphere is the half above the Equator. It holds all of North America and Europe, almost all of Asia, about two-thirds of Africa and a small part of South America. It also contains the Arctic Ocean and the North Pole.
The northern half has much more land. It holds about 67 per cent of all Earth’s land, and land covers about 39 per cent of its surface. It also holds most of the world’s people. In 2015, about 6.4 billion of the world’s 7.3 billion people lived in the north, roughly 87 out of every 100. All of the world’s most populous countries, India, China and the United States, are in the Northern Hemisphere.
The Southern Hemisphere: Australia, Antarctica and a lot of ocean
The Southern Hemisphere is the half below the Equator. It contains all of Antarctica, all of Australia and New Zealand, most of the Pacific islands, about 90 per cent of South America and about one-third of Africa. Countries entirely in the south include Australia, New Zealand, Argentina, Chile, South Africa and Madagascar.
The south is mostly water. Sea covers about 81 per cent of its surface. That includes the whole Southern Ocean around Antarctica and most of the Indian Ocean. In 2015 that left only about 0.9 billion people in the south, roughly 13 out of every 100. Because water warms up and cools down slowly, all that ocean makes southern seasons a little milder than northern ones at the same distance from the Equator.
Eastern and Western: China, Canada and the 180° line
The Prime Meridian only makes half of the east–west cut. On the opposite side of the world is the 180° meridian, which runs mostly through the Pacific Ocean. The Western Hemisphere is everything west of Greenwich and east of the 180° line. The Eastern Hemisphere is everything else.
The Western Hemisphere holds North America and South America, plus the western tips of Europe and Africa, such as Portugal, Ireland and Senegal. Iceland and Cuba are in it too. The largest country completely in the Western Hemisphere is Canada, at 9,984,670 km². The middle of the Western Hemisphere is in the Pacific Ocean among the Galápagos Islands, which belong to Ecuador.
The Eastern Hemisphere holds most of Europe and Africa, nearly all of Asia, and Australia. The largest country completely in it is China, at 9,596,961 km². Russia is even bigger, but it does not count, because a small corner of its far east, in Chukotka, pokes across the 180° line into the Western Hemisphere. The United States works the other way round: some of Alaska’s Aleutian Islands, and Guam, lie in the Eastern Hemisphere.
Countries cut by the lines: Ecuador, Algeria and Kiribati
Some countries are split in two by one of the lines. Ecuador in South America is named after the Equator. Its name is simply the Spanish word for it, and the country’s full name means “Republic of the Equator.” About 26 km north of the centre of Quito, the capital, stands a monument called Ciudad Mitad del Mundo, which means “Middle of the World City.”
The monument is 30 metres tall and has a globe on top that is 4.5 metres wide and weighs 5 tonnes. It celebrates a French–Spanish science team that included Louis Godin, Pierre Bouguer, Charles Marie de La Condamine and Jorge Juan. In 1736 they came to the area to test whether the Earth is slightly flattened at the poles. (It is!)
Brazil, Colombia and the other equator countries listed earlier are also split between north and south. On the east–west line, Algeria is the biggest country cut by the Prime Meridian. It is the largest country in Africa, at 2,381,741 km², and most of it lies east of the line.
But the champion is Kiribati, a country of coral islands in the middle of the Pacific Ocean. Its islands are spread out so widely, from Banaba in the west to Kiritimati in the east, that both the Equator and the 180° line cross the country. That makes Kiribati the only country with land in all four hemispheres. In 1995, Kiribati even moved the International Date Line, the line where the calendar day changes, far to the east, so that the whole country would share the same date. As a result, its eastern Line Islands are in the world’s earliest time zone, UTC+14, among the very first places on Earth to welcome each new day.
Christmas in summer: why Sydney and London swap seasons
The most exciting difference between the hemispheres is the seasons. The Earth is tilted on its axis by about 23.4°. As it travels around the Sun, the tilt stays pointing the same way. For half the year, the Northern Hemisphere leans towards the Sun. It gets more direct sunlight and longer days, so it has summer, while the Southern Hemisphere leans away and has winter. Six months later, they swap.
That means the seasons are flipped. In Sydney, Australia, January is the middle of summer, with average afternoon temperatures of 27.7 °C. At the same time in London it is winter, with afternoons averaging just 8.4 °C. In July it is the other way round: London averages 23.9 °C in the afternoon, while Sydney cools to 17.7 °C. So in Australia, Christmas falls in the middle of summer, and many families celebrate outdoors or at the beach. In New Zealand, South Africa and Argentina, too, December means sunshine and long days, while June brings the shortest days of the year.
What about places right on the Equator, like Kenya, Indonesia or Ecuador? There, the Sun is high in the sky all year, so there is hardly any summer or winter at all. Instead, many equator countries have rainy seasons and dry seasons.
Now find your own home on a map. Is it above or below the Equator? East or west of Greenwich? Write down your two hemispheres. Then learn how to pinpoint any place on Earth with our guide to latitude and longitude for kids, take a closer look at the middle line in the Equator for kids, or see what a hot Christmas and a chilly July feel like in our guide to the seasons in Australia.