Since we’re hanging out at the South Pole, let’s take a minute and do some sight-seeing. Maybe you’re wondering what sights there could possibly be on a continent almost entirely covered with ice. Don’t worry. What we’re interested in isn’t found on the ground. It’s high up above our heads, in the night sky: The Aurora Australis, also known as the Southern Polar Lights.
Beautiful!! These brilliant lights get their name from Aurora, the Roman goddess of dawn. “Australis” is a Latin word, and means “of the South”. The Aurora Australis are only visible at night in the farthest Southern regions of the Earth, in Antarctica, South America, and Australia. But these are not the only places we can go to see auroras.
There are Northern Polar Lights, too. They are brightest near the North Pole, but are sometimes visible from many locations in the Northern Hemisphere all over the world. Another name for the Northern Lights is Aurora Borealis. “Borealis” comes from the Greek name for wind. Both Southern and Northern Lights look like colourful curtains draped over the night sky, swaying in the wind.
Most people have heard of the Northern and Southern Lights before, and many people have even seen them for themselves. But have you ever thought about what these lights are, and why they are brightest at the North and South Poles?
There are a few different things at work. First, there is an invisible magnetic field (called the magnetosphere) that surrounds the Earth. We do not really understand the origins of this magnetic field, but it probably has something to do with the Earth’s rotation, and the materials that make up its core. An easy way to think about the magnetosphere is to imagine a giant bar magnet running through Earth, at a slight angle. One end is near our North Pole, and the other end is near the South Pole.
Earth’s magnetosphere is always changing and moving. This means that the North Magnetic Pole is not the same as the North Pole on the map (called Geographic North Pole). Same goes for the South Pole. As you can see in the illustration above, the imaginary magnetic lines are closest together near the Earth’s Geographic North and South Poles, which means that these areas are where the magnetic field is strongest. This is why auroras only show up near the poles. But we need more than an invisible magnetic field to make Aurora Australis and Borealis.
Next, we need some Solar Wind. Electrically charged tiny little particles that make up the Sun’s atmosphere are constantly boiling off and flowing into space at extremely high speeds. This creates Solar Wind. It is what blows a comet’s tail away from the comet as it flies through space.
Solar Wind is also what powers our beautiful Northern and Southern Lights. It pushes on the Earth’s magnetosphere and changes its shape. The Solar Wind squishes the magnetic field on the side of Earth facing the sun as it flows over us, and stretches it into a long tail called a magnetotail behind us.
Some of the charged particles from the Solar Wind are also being pulled towards the Earth by the magnetosphere itself. When conditions are just right, the magnetotail funnels them towards the magnetic poles. Once in the upper layer of our atmosphere, these particles crash into gas atoms (tiny little invisible particles that make up the air you breathe), which creates energy. So far, this entire process has been invisible. Now things become exciting. The energy is released as light! The colour of the light depend on what kind of gas atoms the particles crash into, which varies depending on how high up in the atmosphere this crash occurs.
Now you know! Isn’t science beautiful?