Dance of light

Through the vast sky she flies, spreading her light ; green ,blue, red, yellow and pinkish hue and the night sky becomes a play of light . She is “Aurora” the Roman Goddess of dawn blessing and bringing the night sky to life.

Well its not some divine glow lighting up the sky around the polar regions although it was believed so, It is Aurora Borealis( Boreas greek for ‘north wind’) in northern hemisphere and Aurora Australis (latin for 'of the south’) in the southern hemisphere. They are brought about by the solar wind particles(more on solar winds in the next post on Coronal Mass Ejection) colliding with the particles in the earth’s upper atmosphere exciting them .The excited particles relax by transferring their energy to others and/ or emitting a photon. Check out these beautiful pictures taken from places like Alaska and North Canada

And Aurora Australis captured by NASA's IMAGE satellite:

Although its occurs everywhere, being a phenomenon of upper atmosphere, it is more clearly visible as one goes farther away from equator and during equinoxes ( guess the reason!)

So what exactly happens when there is collision of solar wind particles with the atmosphere? It either ionizes or excites the oxygen and nitrogen atoms in the atmosphere(the two most common elements in the atomsphere). So if a nitrogen atom is ionized, on getting back an electron it emits blue light.

If it had just got excited, it emits red light and comes to its normal ground state.

The colour of light when an excited oxygen atom comes back depends on its initial excitation and the time it takes to come back to ground state. Green light is given if it comes down within three quarters of a second; red if it takes more time. If it gets to collide some neighboring atom and transfer its energy then none at all.

Do u think the colour is going to be altitude dependent? ( No, not your altitude , I mean the atom’s)

Auroras aren’t restricted to Earth. Solar wind and the planet’s magnetic field brings about a similar recreation of what we observe on earth. This ones from Jupiter:

I leave you gaping with these youtube video. May be try living the moments that we , near the equator don’t get to see.

References:

http://en.wikipedia.org/wiki/Aurora_%28astronomy%29