Intermediate Reading Exercise

The Northern Lights: What Are They?

For centuries, people in the northern parts of the world have watched the sky dance with spectacular curtains of green, pink, and purple light. This breathtaking natural event is known as the Aurora Borealis, or the Northern Lights. For a long time, its cause was a complete mystery, leading to many myths and legends. Today, however, science can give us a clear explanation for this beautiful phenomenon.

It all begins with the sun. The sun is constantly sending out a stream of electrically charged particles into space. This stream is known as the solar wind. After travelling millions of kilometres, some of these particles reach our planet. Fortunately, the Earth has a powerful magnetic field which protects us from most of this solar radiation. This magnetic field is weakest at the North and South Poles, and it acts like a funnel, pulling the solar particles down into our atmosphere in these polar regions.

The 'magic' happens when these high-energy solar particles collide with atoms and molecules of gas high up in our atmosphere, typically between 100 and 400 kilometres above the Earth's surface. This collision transfers energy to the gas atoms, making them 'excited'. But they cannot stay in this excited state for long. To return to their normal state, they must release this extra energy in the form of tiny flashes of light. When billions of these collisions happen at once, they produce the incredible light show we see from the ground.

The different colours of the aurora are determined by which type of gas is being hit, and at what altitude. The most common colour, a bright green, is produced when solar particles collide with oxygen atoms at about 100 to 300 kilometres high. Red lights, which are rarer, are also caused by oxygen, but at much higher altitudes above 300 kilometres. Pink and dark red colours can be created by nitrogen molecules.

The best places to see the Northern Lights are in the 'auroral zone', which includes countries like Iceland, Norway, Sweden, Finland, and parts of Canada and Alaska. They are most visible on clear, dark nights between September and March, when the nights are longest. While scientists can forecast the probability of seeing the aurora, they are a natural phenomenon and can never be completely predictable. This unpredictability is part of what makes seeing them such a special and unforgettable experience. It's a powerful reminder of the dynamic connection between our planet and the sun.