An Aurora is a beautiful pattern of light that can sometimes be seen in the sky at night. The sky gets a glow with brilliant green, red, blue and yellow colours. An aurora near the North Pole is called Aurora Borealis, or the Northern lights. An aurora near the South Pole is called as Aurora Australis or the Southern lights. Sometimes both the phenomena are called “Aurora Polaris”. But what exactly are auroras?
Systematic scientific studies in this field began in 1716, when a spectacular aurora appeared in Europe and was visible in the entire continent. The English astronomer Edmund Halley proved a relation between auroras and the earth’s magnetic field. The most widely accepted theory about their origin is as follows.
We know that our sun is a hot ball of fire. It produces heat due to fusion reactions. As a result, charged particles like protons, electrons, etc. constantly flow out of the sun. The flow of these charged particles is called solar wind. These particles travel through space in all directions at a speed of 480 km per second. As they enter the Earth’s atmosphere, they are attracted by the Earth’s magnetic field. The magnetic north and south poles change the direction and speed of these particles. These particles then collide with air molecules in the cold, thin upper atmosphere. This causes ionization, resulting in the production of coloured lights. These coloured lights are called Auroras.
Auroras are most pronounced, when the Earth’s magnetic field is most disturbed or when there is an unusual increase in solar activity.
Aurora Borealis is most frequently seen around 70° north latitude, while Aurora Australis is seen around 70° south latitude. They are usually seen at heights of 80 km. Some may be as high as 1000 km. These phenomena have numerous forms. Some are like curtain arcs, while others are like rays and fan shaped coronas. They often produce crackling sound in the sky. They apparently move so fast that they are also called the ‘Merry dancers’.
Some of the best displays of these natural lights can be seen around the Hudson Bay region in Canada, Northern Scotland, Southern Norway and Sweden. They are also seen in South Australia and Sri Lanka. At one time, the natives of Sri Lanka regarded them as messages from Lord Buddha!