Northern and Southern Hemispheres: What are the differences between them?

And the science behind those differences.
Maia Mulko

Ever since we learned that the Earth is a sphere, we’ve been able to divide it into four hemispheres. 

A hemisphere is half of a sphere. The Northern and Southern Hemispheres mark the two halves of the Earth horizontally, while the Western and Eastern Hemispheres do it vertically.

Earth hemispheres
Source: Zappys Technology Solutions/Flickr

There are not many geographical differences between the Western and Eastern Hemispheres, but there are geographical differences between the Northern Hemisphere and the Southern Hemisphere.

Here are they. 

 

What is the Northern Hemisphere?


The Northern and Southern Hemispheres are divided by the Equator, an imaginary line located at 0 degrees latitude. 

Monument to the Equator
The Monument to the Equator highlights the exact location of the Equator at 0º0'8" latitude in Mitad del Mundo, Ecuador. Source: Diego Delso/Wikipedia

 

Locations on Earth are determined by latitude and longitude. Latitude is a measure of the angular distance of a place north or south of the Earth's equator, while longitude is the angular distance of a place east or west of the Greenwich meridian (the location was agreed on at a conference in 1884). Lines of latitude are also called parallels because they are parallel to the equator and to one another.

There are 360 degrees of longitude and 180 degrees of latitude. However, to add precision, each degree can be broken into 60 minutes, and each minute can be divided into 60 seconds. This means that any location on Earth can be described in terms of degrees, minutes, and seconds of longitude and latitude.

Degrees of latitude are parallel, so the distance between each degree remains more or less constant. However, because the Earth is slightly elliptical, there are small variations — while each degree of latitude is about 69 miles (111 km) apart, at the equator and the poles, this distance is slightly more than 69 miles, and at the Tropic of Cancer and Tropic of Capricorn, the distance is slightly less. 

    The distance between degrees of longitude varies depending on location — they are farthest apart at the equator and converge at the poles. So, at the equator, a degree of longitude is 69.172 miles (111.321 km), at 40 degrees north or south, the distance between each degree of longitude is 53 miles (85 km), and at the poles, the distance is zero.

    latitude and longitude
    Source: Rajneesh Kumar Thakur/Wikimedia Commons

    The Northern Hemisphere is the half of Earth that lies north of the Equator. It contains around 67% of the Earth’s land mass, including all of Europe, North America, Central America, the Caribbean islands, the northern part of South America, Asia’s continental mainland, and the northern two-thirds of Africa (from Libreville in Gabon to Mogadishu in Somalia). Around 87% of the Earth’s population lives in these areas.

     

    What is the Southern Hemisphere?

    The Southern Hemisphere is the half of the Earth that is south of the Equator. It consists of around 81% water, compared to the Northern Hemisphere, which is comprised of around 60% water.

    southern hemisphere
    Source: SaltedSturgeon/Wikimedia Commons

     

    With respect to land, the Southern Hemisphere comprises Australia, the microcontinent of Zealandia (of which New Zealand and New Caledonia are the largest parts above water), most of the Pacific Islands, most of the South American continent (roughly from the Amazon River in Brazil to the north of Quito in Ecuador), the region of Maritime Southeast Asia (including the Philippines, Brunei, East Timor, Indonesia, Malaysia, and Singapore), Antarctica, and around one-third of the African continent. 

    This is only around 32.7% of Earth's land and is home to more than 800 million people. While that might look like a large number, it is actually just 10-12% of the world’s population. 

     

    Differences between the Northern and Southern Hemispheres

    The Northern and Southern Hemispheres are not only differentiated by the percentages of land and water they have (and the number of people living in them — which is related to the amount of land). 

    There are other differences that are based on this population disparity. As the Northern hemisphere is much more populated, it also has more vehicles and industry so is much more polluted. 

    Air pollution in Tehran
    Heavy air pollution in Tehran, Iran. Source: Hamid Vakili/Wikimedia Commons

     

    According to a 2014 study by Wageningen University and Research Center, the atmosphere in the Northern Hemisphere has roughly the same amount of atmospheric cleaning agent hydroxyl (OH) as the Southern Hemisphere — which is not enough to remove the excess air pollution in the north of the Equator. As there is more pollution in the Northern Hemisphere, removing this requires about 25% more OH than appears to be present. The result is a build-up of pollutants.

    In fact, human-produced air pollutants in the Northern Hemisphere are only found in the troposphere (the lowest layer of the atmosphere, ranging from the Earth's surface to around 10–15 km) but also in the stratosphere (the second layer of the atmosphere). This was revealed by scientists from NOAA’s Chemical Sciences Laboratory and CIRES during an airborne research mission by NOAA and NASA in 2021. 

     

    Seasonal differences

    Due to the Earth’s axial tilt (currently at 23.4°), there is a difference in the seasons in the Northern Hemisphere and the Southern Hemisphere. When the Earth's axis points towards the Sun, it is summer for that hemisphere; when the Earth's axis points away, it is winter. While winter in the Northern Hemisphere starts on December 21st, winter in the Southern Hemisphere starts on June 21st. 

    That is the date on which summer starts in the Northern Hemisphere. But in the Southern Hemisphere, summer occurs from December 21st to March 21st. 

    To put it simply: 

     

    Season

    Northern Hemisphere

    Southern Hemisphere

    Autumn

    September 21st - December 21st

    March 21st - June 21st

    Winter

    December 21st - March 21st

    June 21st - September 21st

    Spring

    March 21st - June 21st

    September 21st - December 21st

    Summer

    June 21st - September 21st

    December 21st - March 21st

     

    While the Southern Hemisphere should be warmer because it has more water, and water retains heat much better than land, in reality, the Northern Hemisphere is warmer. Research suggests this is largely due to the North Atlantic heat pump. This is a northward-moving mass of warm water and part of the global thermohaline circulation, which is the movement of ocean currents caused by differences in temperature and salinity in different regions of water. The heat pump is driven by cold, salty water in the North Atlantic sinking and pulling warmer, less-salty surface water from the tropics to replace it. Heat is released into the Northern Hemisphere's atmosphere from the warm water. However, because there is no return flow of warm water to the Southern Hemisphere, the warmer air is trapped in the north.

     

    The Coriolis effect

    The Coriolis effect describes the deflection taken by objects not firmly connected to the ground as they travel long distances around Earth due to Earth's rotation. The Coriolis effect was first explained by French mechanical engineer Gaspard-Gustave de Coriolis in an 1835 paper about fluid dynamics in water wheels and is responsible for many large-scale weather patterns.

    The Coriolis effect is due to the fact that the Earth rotates faster at the Equator than it does at the poles. This is because the Earth is wider at the Equator, so in order to make one rotation every 24 hours, the equatorial regions move nearly 1,600 kilometers (1,000 miles) per hour while the area near the poles rotates at just 0.00008 kilometers (0.00005 miles) per hour.

    Fluids, such as air currents, which travel across large areas, appear to bend to the right (east) in the Northern Hemisphere and to the left (west) in the Southern Hemisphere.

    The Coriolis effect helps create regular wind patterns around the globe, such as the movement of cyclones and trade winds.

    For example, in the Northern Hemisphere, this air deflection to the east means that cyclones and hurricanes appear to rotate counter-clockwise. In the Southern Hemisphere, currents are deflected to the west, so storm systems seem to rotate clockwise.

    Trade winds are created because warm air rising near the Equator flows toward the poles. In the Northern Hemisphere, these warm air currents are deflected to the east as they move. As the current descends, it consistently moves from the northeast to the southwest, back toward the Equator.

     

     

    Star luminosity 

     

    People in the Northern Hemisphere don’t see the same night sky as people in the Southern Hemisphere.

    Due to the Earth’s tilted axis, the Southern Hemisphere is best for observing dense regions of stars because at a latitude of –30 degrees (30 degrees south), the galactic center of the Milky Way is directly overhead. The Northern Hemisphere faces toward the edge of the Milky Way, so the galactic center doesn’t rise as high above the horizon in the winter, and it gets washed out by the Sun in the summer.

    This means that the stars and constellations look brighter when observed from the Southern Hemisphere. This is good if you are trying to observe the center of the Milky Way and its dust clouds, but the brightness of the stars can actually obscure the view if you are trying to see something else. 

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