Legends of the light- Northern lights

The mystery of the beautiful northern lights has been disturbing many of us since our childhood. So let’s start from the very beginning-

 What are northern lights?

Northen lights are the bright dancing lights giving a beautiful colour display on the poles, both northern and southern. They are known as 'Aurora borealis' in the north and Äurora australis'in the south. In the early 17th century Galileo called this phenomenon Aurora Borealis. Aurora was the roman goddess of dawn, and Boreas was the greek name for the north wind. He thought that an Aurora was caused by the sunlight reflected from the atmosphere.         

What causes the northern lights?

The temperature above the surface of the sun is very high. At this temperature, collisions between gas molecules are frequent and explosive. Free electrons and protons are thrown from the sun's atmosphere by the rotation of the sun and escape through holes in the magnetic field.

These charged particles are blown towards our earth by the solar wind. The charged particles are then deflected by our earth’s magnetic field. However, the magnetic field is weaker at the poles (why?). So, some charged particles enter the atmosphere and start colliding with the gas particles. As a result of these collisions, light is emitted.

How is the colour variation caused?

Variation in colour depends on the type of the gas particles that collide. Oxygen molecules located at 60 miles above produce a pale yellowish-green colour ( the most common). The red auroras (rare) are produced by the Oxygen located at 200 miles above the earth. Blue and purplish red auroras are produced by the molecules of the nitrogen gas. The lights of the Aurora generally extend from 80 kilometres (50 miles) to as high as 640 kilometres (400 miles) above the earth's surface.

When can I see it?

As explained above these dancing lights can be seen on the north and south poles. Auroral displays can also be seen over the southern tip of Greenland and Iceland, the northern coast of Norway and over the coastal waters north of Siberia. Southern auroras are not often seen as they are concentrated in a ring around Antarctica and the southern Indian Ocean. Areas in the north, in smaller communities, tend to be the best. The auroral activity is cyclic, repeats after every eleven years. The last period was on 2013. Winter is the best season to observe these beautiful lights because of the extended and clear nights.

Knowledge Booster-

Why is Earth's magnetic felid weaker at the poles?

The magnetic field is strongest at the centre and weakest at the poles. It is because of the magnetic force lines that are vertical at the poles. These lines are parallel to the earth at the equator. The compass needle points most strongly at central low latitudes and gets progressively weaker as one gets more northerly and southerly.