For thousands of years, the mankind has been mesmerized by the beautiful, pale greenish blue haze adorning the night sky. This captivating phenomenon seen near poles of the earth are called as Aurora Borealis or Northern Lights. These glowing lights are called Aurora Borealis in the north pole and Aurora Australis in the south pole.The term Aurora Borealis, which means ‘dawn of the north’ in Latin, was first coined by famous scientist Galileo Galilei.
Myths about Aurora Borealis
Vikings believed that the northern lights formed a bridge for Greek Gods to descend to earth.
A Norse legend claims that Aurora Borealis is the effect of light reflected from Valkyrie shield.
People in olden days believed that child birth under the northern lights was less painful. In ancient China, it was believed that bright lights illuminating their night sky were a result of battle between good and bad fire-breathing dragons.
Northern Lights Formation
It is safe to say that all myths regarding Aurora Borealis are false. There is a simple scientific explanation that will help us understand why northern lights are formed.
To explain how northern lights are formed, it is important to understand the following:
Plasma and Solar wind.
Earth’s magnetic field.
Reaction between Solar wind and Earth’s magnetic field.
Plasma and Solar Wind
Normally, there are only three states of matter (solid, liquid and gas) found in day-to-day life.
But inside the sun, in extreme tempratures of 14 million degree celcius, an ionized gas containing free electrons and positive ions are formed. It is called plasma. This ionized gas is ejected from the Sun’s surface at a very high speed forming the Solar wind. The Solar wind blows the charged plasma further and further away from sun.
Earth’s Magnetic Field
At the center of the earth lies molten iron in large quantities. Since the gravitational force is greater at the center of the earth, it disturbs the molten iron and thus forms a magnetic field that shoots out from the earth’s center. The earth’s magnetic field forms a layer over our atmosphere called Magnetosphere. This layer shields earth from charged ions travelling in the outer space.
It is to be noted that earth’s magnetic field is stronger towards the center and weaker near the two poles.
Solar Wind vs Earth’s Magnetic Field
What would happen if solar wind carrying plasma reacts with earth’s magnetic field? Let’s find out. When solar wind reaches earth’s atmosphere, the magnetic field of earth deflects the free electrons and positive ions of plasma. These charged particles then move towards the north pole and south pole of earth where magnetic field is weak. So, the particles of plasma enter earth’s atmosphere through the two poles.
Different Colors of Northern Lights
When the charged particles react with oxygen and nitrogen in earth’s atmosphere, it produces beautiful bright lights across the sky that we know as northern lights. If electrons bombard oxygen upto a level of 150 miles from earth’s surface, then it produces a pale green-yellowish color. If charged particles react with oxygen that is higher than 150 miles, then it produces red color. And, if the ions collide with nitrogen, then it produces a soothing blue color.
