April is the time when the auroras create magic in the skies over the north and south poles, says Shatavisha Chakraborty
FOR MILLENNIA, light has been a source of speculation, superstition and awe for mankind. And if the light we are talking about are bright red, green, yellow, pink and purple streaks of colours always moving in beautiful patters, then surely there is nothing more enthralling and magical than this. Such luminous curtains seen in the far North and South skies are known as the auroras.
In 1616, Galileo Galilei studied this extraordinary phenomenon. But of course the dancing lights have dazzled people for a long time before him. The 30,000-year-old cave paintings in France are a testimony to this fact.
The most spectacular example of the way that the sun and earth are invisibly connected is the phenomenon of the Aurora Borealis (Northern Lights) and the Aurora Australis (Southern Lights). But what causes such bright streaks of light to dance in the middle of nowhere?
The cause of formation of the auroras is actually quite simple. But the fact that these auroras ‘dance’ can be attributed to the magnetic reconnection which is responsible for the sudden increase in brightness and movement of the auroras. Magnetic reconnection is a process were magnetic lines are broken and reformed giving off kinetic energy and heat. The earth’s magnetic field lines capture and store the energy and magnetic reconnection occurs when these stressed lines suddenly take up new shapes. This complete phenomenon has been investigated by NASA.
When a major solar storm buffets earth’s magnetic field, it causes some parts of this field to rearrange itself. This releases energy that causes powerful currents of particles to flow from distant parts of the magnetic field, into the atmosphere. An interesting point to be noted is that these particles did not originate from the Sun, but were already trapped in the magnetic field. Once they reach a charged layer of the atmosphere called the ionosphere, they pick up still more energy and the currents of fast-moving charged particles continue to flow along the magnetic field into the polar regions and collide with nitrogen and oxygen atoms in the atmosphere. These collisions produce deep red glows as high up as 1,000 km above the ground and beautiful curtains of green and blue light at altitudes as low as 90 km. They never reach the ground, though they can sometimes seem to do! Auroras are generally quite bright with the strongest auroras comparable even to moonlight.
Are the auroras seen only on earth? The answer is no. Any planet with a sufficiently dense atmosphere will have auroras. But planets like Venus have no magnetic field so they experience irregular-shaped auroras. On earth, auroras are observed only near the poles. So planets whose magnetic axes are very different from their rotational axes have severely distorted forms of auroras. NASA has photographed auroras on Jupiter, Saturn and on the moons of some planets. Auroras are not seen on our moon obviously because it does not have the appropriate atmosphere.
Scientists have marked rings known as ‘auroral ovals’ that run roughly around the Arctic and Antarctic circles where the aurora is most likely to be seen. At the busiest point in the 11-year circle of solar activity, auroras are observed over a much wider span of latitudes. So if you are interested in experiencing the beauty of the auroras yourself you would better head to the Arctic Circle that provides a far more hospitable weather conditions than its Southern counterpart.
As colour after colour, day after day a new colour is made into the swirl in the sky, the magnificent and heavenly auroras make me feel that if Iris, the goddess of the rainbow, takes up a new incarnation it would be as the goddess of Auroras. The glowing arcs of the auroras that are ever so dynamic that they remind us of our life that is not static even for a moment. It doesn’t really matter what you call them – heavenly lights, gates to heaven, rainbow in the sky, all of them are the same. Auroras will always be there colours and all.