Why Auroras emit 8 streams of coloured light?

Why Auroras emit 8 streams of coloured light?

PROF WAQAR HUSSAIN

             

     Aurora has literal meaning “sunrise”; Aurora is also name of Roman goddess of dawn. Aurora in Urdu is called Kutub raushani(light of poles).It is a luminous meteoric phenomenon of electrical character seen about 80 km above  Polar Regions with a tremulous motion and giving forth streams of eight Aurora or curly coloured dashing storm of light. This illumination of sky flowing from North Pole is called Aurora Borealis(Boreas means north wind) or Northern Lights, and streaming from South Pole is called Aurora Australis or

Southern Lights. They are actually caused by radiation from the sun-spots. A stream of electrons thrown out from the solar cyclone reaches the atmosphere of the earth and there strike the gases in the upper atmosphere, it causes them to vibrate, excite, glow and flow.

            Northern lights are caused by collisions of fast moving electrons (coming from space) with oxygen, nitrogen and other gas molecules present 

in our atmosphere. These electrons originate from the sun. The outermost surface of sun corona has temperature of 2 million ^oC and emits solar wind containing free electrons and positive ions. Solar wind reaches earth with speed of 400km/s and magnetic field of 2-5 nanoteslas. This speed and magnetic field increases several times during magnetic 

storm. Earth magnetosphere is formed by the impact of solar wind on earth magnetic field which blocks solar wind. Still some potion travel toward the poles.

               Electrons of solar wind collide with electrons of oxygen and nitrogen molecule. As a result, electrons of oxygen and nitrogen are excited i.e. they shift to high energy state or oxygen and nitrogen lose their own electrons to form ions. 

When excited electrons return to normal ground state, energy is released in the form of radiation of different colour and form aurora. Oxygen generally gives greenish –yellow or red light while nitrogen gives off blue light.