Closer to the poles, the sky stages a wondrous show of colour and light. For thousands of years, humans gazing at the stars beheld this grand cosmic dance. The ‘Aurora’ has fascinated the curious star-gazer and the romantic poet.
An aurora is caused when solar wind, with a steady stream of charged particles – protons and electrons – emanated by the sun, collides with the atmosphere. These particles come in contact with ionospheric molecules, releasing energy that light up a dark sky. Solar particles literally travel at the speed of light, translating to 500 seconds as the time needed for energy from solar flares to hit Earth, which is a little over eight minutes after it leaves the Sun.
While most of these particles are deflected, some are trapped in the Earth’s magnetosphere, accelerating towards the North and South poles into the atmosphere. This explains the phenomenon’s concentration around the magnetic poles. The forms of aurora within bands around both polar regions is dependent on the acceleration imparted to the precipitating particles.
Auroras have been noticed forming different shapes across a range of hues, predominantly green, red and purple, depending on the atoms colliding with solar wind. Besides the light show, like many other celestial mysteries, scientists have discovered auroras emitting sounds -- of a hissing, crackling and clapping type. Also, most planets, natural satellites, dwarf planets, and comets are known to host auroras.
Names with a rich past
Towards the North Pole, the phenomenon is called ‘Aurora Borealis’, or the Northern Lights, derived from the Roman goddess of dawn, ‘Aurora’, and Greek for the north wind, ‘Boreas’. Italian astronomer Galileo Galilei is credited with the christening of ‘Aurora Borealis’. Likewise, the Southern Lights, over the South Pole, was termed ‘Aurora Australis’ by Captain James Cook. ‘Australis’ is Latin for southern. In the 19th century, Norwegian scientist Kristian Birkeland was the first to explain the source of auroras, establishing the ‘Sun-Earth Connection’ theory.
However, archaeologists suggest that certain cave drawings from 2,600 BC in China could be the earliest depiction of auroras in the sky, while most succeeding civilisations have witnessed this phenomenon unfold above their heads.
Auroras need an ideally dark sky to behold them with each burst lasting up to 30 minutes. There is also an Aurora Season, in March and October around the equinox, when the phenomenon is at its peak. Places which offer the best views of the Northern Lights are Russia, Scandinavia, Canada, Scotland, Greenland, Iceland, the Baltic, and the US, while Southern Australia, Southern Argentina, New Zealand, and Antarctica, are perfect to spot the Southern Lights. Recently, an aurora burst was also captured over Ladakh in India, while the ISS crew are gifted with more mesmerising views.