When the charged particles from the sun strike atoms and molecules in Earth’s atmosphere, they excite those atoms, causing them to light up.
But first let us understand what it means for an atom to be excited?
Atoms consist of a central nucleus and a surrounding cloud of electrons encircling the nucleus in an orbit. When charged particles from the sun strike atoms in Earth’s atmosphere, electrons move to higher-energy orbits, further away from the nucleus. Then,when an electron moves back to a lower-energy orbit, it releases a particle of light or photon.
Now a question arises as to how the charged particles from the sun strike atoms and molecules in the Earth’s atmosphere?
The temperature above the surface of the sun is millions of degrees Celsius. 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. Blown towards the earth by the solar wind, the charged particles are largely deflected by the earth’s magnetic field. However, the earth’s magnetic field is weaker at either pole and therefore some particles enter the earth’s atmosphere and collide with gas particles.
The Aurora Borealis originates some 93,000,000 miles away on the surface of the Sun with a massive explosion of electromagnetic matter called a Coronal Mass Ejection (CME).
What is CME?
Every so often, the sun burps, with the power of 20 million nuclear bombs. These hiccups are known as coronal mass ejections or CMEs. They are powerful eruptions near the surface of the sun, driven by kinks in the solar magnetic field. The resulting shocks ripple through the solar system and can interrupt satellites and power grids on Earth.
During a CME, enormous bubbles of superheated gas – called plasma – are ejected from the sun. Over the course of several hours, a billion tons of material are lifted off the sun’s surface and accelerated to speeds of a million miles per hour (1.6 million kilometers per hour). This can happen several times a day when the sun is most active. During its quieter periods, CMEs occur only about once every five days.
CME’s usually emanate from the more active areas of the Sun’s surface and they throw a stream of electronically charged solar particles known as Solar Wind into the vastness of space. It is when these particles are directed towards the Earth that we can see the Northern or Southern Lights three or four nights later.
The Solar Wind approaches the Earth and causes a distortion in our magnetic field and, whilst most of the particles are deflected away from us, some escape into our atmosphere around the magnetic poles. At this point, the “escaped” particles collide with the atoms and molecules that form the gases in our atmosphere and cause them to become “excited”. When an “excited” atom or molecule begins to calm or return to its original state, it emits photon energy in the form of light.
It is the emissions of these photons on a huge scale that causes the Aurora to appear in our night sky.
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