AURORA LIGHT

The auroras in Earth’s Northern Hemisphere are called the aurora borealis. Their southern counterpart, which light up the Antarctic skies in the Southern Hemisphere, are known as the aurora australis.  

 HOW IT IS FORMED?

Sun’s corona (outermost atmosphere) consists of the fourth state of matter, i.e. Plasma (collection of charged particles). This Plasma is continually heated up to the point that the sun’s gravity cannot hold them. It then travels along the sun’s magnetic field lines that extend radially outward. As the sun rotates, it winds up its magnetic field lines above the polar regions, creating a constant stream called as solar wind.

In the centre of the earth, hot iron is present, which is rolling around due to tremendous gravitational pressure. This creates the magnetic field lines around the earth. This is also called as Magnetosphere. These lines are rarer at the poles.

The positive ions (particles of plasma) from the solar wind, coming from sun’s corona strikes over the magnetic field lines of the earth. As the particles pass through the earth’s atmosphere at the northern and southern poles due to weaker magnetic field, they reacts with the atoms and molecules of the oxygen, nitrogen and other elements. The electrons tend to release energy and excites the atoms. Thus oxygen, nitrogen and other elements release their energy in the tiny packets of photons. Therefore we can see the light of different colors.

WHAT CAUSES COLOURS?

Aurora borealis mainly comprises of pink, green, yellow, blue, violet and occasionally orange & white. Particles which collides with oxygen forms yellow and green light whereas red, violet and occasionally blue light is formed due to collision with nitrogen.

Type of collision makes difference for displaying various colors. For example, blue displays by the atomic nitrogen and purple by that of molecular nitrogen.

We can observe the effect of altitude on the colors. Up to 150 miles (241km) height, green light can be seen. Above 150 miles, red color is observed.  Up to 60 miles (96.5km), blue is displayed and above 60 miles, purple and violet colors are seen. These lights can be static band of light or even can be seen as dancing with changing colors when solar flares are strong.

 WHERE TO SEE?

Alaska and Northern Canada are best places to visit however Norway, Sweden and Finland also offers excellent vantage points.

WHEN TO SEE LIGHTS?

 Northern lights are always present, but winter time is best due to less pollution and clean air. September, October, March and April are some of the best months to view this effect. These are more active and brighter up to 2 days after highest sunspot activity. Also some agencies, such as NASA, monitors solar activity and issue Aurora alerts.

REFERENCES:

1. Wikipedia

2. NASA

3. Space Technology

-Mayuri Baraskar