2015 Nov

Physics of Aurora Borealis

November 16, 2015

Physics of Aurora Borealis

We must all have seen a large collection of beautiful photographs on the internet with hanging green and pink lights over a clear night sky. This phenomenon is called the “aurora borealis” when it occurs in the northernmost latitudes and “aurora australis” when in occurs in the southernmost latitudes. This phenomenon occurs at the poles and the concepts involved are strongly correlated to what we learn during the A Level physics tuition classes.

The journey of these beautiful visual formations begins at the upper layer of the sun. The upper layer of the sun consists of plasma moving upwards due to convection and the rotation of the sun cause the plasma to swirl along with the rotation of the sun. This motion of the charged plasma causes a strong magnetic field in and around the sun. For every 11 years there occurs what are called, the “sun maximum” and the “sun minimum” which are a result of the disorder and order in the motion of the plasma and hence the magnetic fields around the sun. During a solar maximum, giant loops of magnetic fields are formed sometimes of the size of the earth. These magnetic fields may break and discharge gigantic volumes of charged particles called Solar winds. The solar winds move at an average speed of about 400 km per second before they reach the earth’s magnetosphere. The solar wind consists and charged electrons and positive ions. The earth’s magnetosphere is the protective magnetic field around the earth magnetic field caused by it. The solar wind upon interaction with the earth’s magnetic field changes the shape of the earth’s magnetosphere away from the direction of the solar wind making it look like an airplane wing being put to a wind test. During this process, energy is rapidly transferred form the gigantic solar winds to the earth’s magnetosphere. This process is called magnetic reconnection. The earth’s magnetosphere protects us from these solar winds which as mentioned travel at over 400 km per second to sometimes at over 1000 km per second. It is still a matter of awe and suspense as to how the thin magnetosphere is able to hold powerful solar winds from entering the lower atmospheric surfaces. Quantum physics is doing a great job at unraveling the mysteries around the earth’s magnetic field. Now, after the magnetic reconnection, the accelerating charged particles in the earth’s magnetosphere upon interaction with the strong magnetic field move in a helical path and upon reaching the earth’s atmosphere cause the beautiful Northern and Southern lights.

The ‘aurora borealis’ or the northern lights and the ‘aurora australis’ or the southern lights can be observed only on a clear night sky. Since the totality of the magnificent atmospheric optical show cannot be captured completely by the naked eye, time lapsed cameras are used. These phenomenon are later studied so as to be able to explain both the type of interactions between the charged particles and the earth’s magnetic field and also the nature of the solar winds and earth’s magnetic field itself.

What was conceived to be the “Dance of the spirits” during the medieval Europe turned out to be a beautiful quantum mechanical phenomenon.

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