Around midnight in the late autumn sky (exactly around this time), if you are in the Northern Hemisphere, near the North Pole, you are likely to witness the most enigmatic light show on earth — the Aurora Borealis or the Northern Lights. The sky seems to glow with rays or curtains of light of green, yellow, blue, or faint red/pink and even violet tints, with their shapes constantly changing and evolving, presenting a spectacular display of light dance that leaves the viewers spellbound.

Long ago, this spectacle left the beholders filled with fear and they came up with many explanations. The Vikings believed that the lights were due to the glow of the spears and armours of Valkyries, who were believed to be immortal, war-like females in Norse mythology, when they galloped in the night sky on their horses.

The Inuits, indigenous peoples of the Arctic regions of Greenland, Canada, and the United States, thought that these lights were the souls of deer, seals, salmon and whales that they hunted. The Menominee Indians, in North America, believed that the Northern Lights came from the torches of giants that lived in the North, while Europeans in the Middle Ages tried to actually ‘read between these lines’ to decode what they thought were messages from God, usually of disasters that were to come. Some even thought that heavenly armies were fighting in the skies!

But what are these lights, surely now with science having explored and discovered the secrets of almost everything in and around Earth, we should know more about Aurora Borealis. First of all, we can see this amazing display of light both near the North and South Polar regions, with the Southern Lights being called Aurora Australis. These regions are typically 10 degree to 20 degrees from Earth’s magnetic poles.

These are formed when particles from Sun, as a result of solar wind, hit the earth’s atmosphere and when these highly charged particles collide with other atoms in the atmosphere, they lose energy and excite gases in the atmosphere to glow and emit a photon of light. The reason why these ‘light rays’ do not fall on Earth and are not seen in other regions is that the Earth’s magnetic poles are located near the Poles. The Earth’s magnetic poles are just like the poles of a giant magnetic bar and so the Solar particles get deviated away from the Earth due to its magnetic force and are thus seen parallel to the Earth, up in the sky as ribbons or waves of light moving in a certain direction.

The colours of these lines of light depend on the composition of the emission that the Solar winds, with green and maroon coloured aurora occurring when the molecules emit oxygen, blue lights occur when nitrogen is emitted and reddish lights indicate either oxygen or nitrogen.

The Auroras occur in different shapes — flowing, moving waves of light (known as Quity Arces), thin strips of light (diffuse patches) or sheets of glowing light (Raide Arces).

These lights are frequently seen in late autumn (September-October) and winter/early spring (March-April) and during the two to three hours around midnight because they are not bright enough to be spotted in the daytime. During the cold winter nights when snowfall starts, you can’t see these lights. These light displays can last for several days. The height of the Auroras is Between 600 (969km) and 60 miles (96km) in altitude.

The shape of the lights depends on the shape of the magnetic field lines and the location of the observer. If the observer is farther south, then the aurora it will appear near the horizon, if he is directly beneath it, it will be seen overhead. Lights that are located directly above often appear more as rays than curtains because of the position of the viewer.

The name Aurora Borealis is made up of the name of the Roman goddess of dawn, Aurora, and the Greek name for the north wind, Boreas, and it was Pierre Gassendi, a French mathematician and astronomer, who coined this name in 1621. Since ancient times, Aurora Borealis have been given more attention than Aurora Australis because there are more people around the North Pole than the Southern Hemisphere. Reykjavik in Iceland is a wonderful place to see the Northern Lights, as are many areas of Alaska, Canada, Greenland, Finland, Norway and Sweden.

Perhaps the most spectacular Northern Lights displays in recorded history is reported to have occurred on August 28 and September 2, 1859, when it was seen as far south as Boston when, New York Times reported, the aurora was “so brilliant that at about 1:00am ordinary print could be read by the light”!

The auroras were the results of a great geomagnetic storm and these occurrences were seen and reported in published scientific measurements, ship’s logs and newspapers throughout the United States, Europe, Japan and Australia. This was also when, for the first time, the phenomena of Auroral activity and electricity were linked, mainly due to the fact that a significant portion of the 125,000 miles (201,000km) of telegraph lines were significantly disrupted for many hours throughout the storm.

But it was only when Kristian Birkeland, a Norwegian scientist, did a series of experiments that the correct theory of the phenomenon was developed in 1908.

However, it was 100 years later, in 2008, that for the first time scientists were about to determine the triggering event for the onset of magnetospheric sub-storms when two of the five THEMIS probes, positioned approximately one third the distance to the moon, “measured events suggesting a magnetic reconnection event 96 seconds prior to Auroral intensification”. Dr Vassilis Angelopoulos of the University of California, Los Angeles, the principal investigator for the THEMIS mission, claimed, “Our data show clearly and for the first time that magnetic reconnection is the trigger”.

Other planets of the Solar System, Jupiter, Saturn, Uranus and Neptune along with some of their moons, also experience such display of lights. The Auroral effect on Venus is a little different than the one on Earth because there is no magnetic field there so the lights are distributed in patches across the entire planet.