Aurora Borealis and Aurora Australis (Northern Lights and Southern Lights)

 

Aurora Borealis and Aurora Australis (Courtesy: pexels.com, Raul Ling and Joshua Hurricks)

The spectacular display of other worldly dancing lights seen in the night sky near northern poles and southern poles named as Aurora Borealis and Aurora Australis also called as Northern lights and Southern lights respectively are a celestial feast for the eyes.

What is the explanation for this natural phenomenon ?

During solar flares, a huge number of charged particles such as electrons and protons are spewed out of the surface of the sun. Some of these particles get trapped by the earth's magnetic field and take a helical path along the field lines to get deflected towards the poles. The field lines are denser closer to the poles. These particles collide with the atoms and molecules of the atmosphere. Excited oxygen atoms emit green light and excited nitrogen atoms emit pink light.

Why the Helix or Helical path?

Moving charged particles when entering into magnetic field experiences a force called Lorentz force. When the velocity of the particle is normal to the magnetic field, it takes a circular path due to the force acting towards the center called centripetal force. When the velocity of the particle is parallel to the magnetic field, it continues its motion without any change as it does not experience any force. When the velocity is in any other angle with the magnetic field, there will be a V normal component and V parallel component, giving rise to a combined motion of linear motion and circular motion called as Helix or Helical path.