Coming across one of the blog entries on rainbows, I immediately thought of the time when I saw the Northern Lights while on holiday. Till date, it is one of the most spectacular and breathtaking phenomenon I have ever seen! The multitude of colors intermingling with each other across the night sky, it is a truly gorgeous sight. Our discussion on light motivated me to read more about how this phenomenon occurs.
The Northern Lights or the aurora borealis are nothing more than a sight caused by the interaction of charged electrons and magnetic poles of the earth. Solar winds stream away from the sun at speeds of about 1 million miles per hour. When they reach the earth, some 40 hours after leaving the sun, they follow the lines of magnetic force generated by the earth’s core and flow through the magnetosphere, a teardrop-shaped area of highly charged electrical and magnetic fields.
As the electrons enter the earth’s upper atmosphere, they will encounter atoms of oxygen and nitrogen at altitudes from 20 to 200 miles above the earth’s surface. The color of the aurora depends on which atom is struck, and the altitude of the meeting. We see green when the electrons encounter oxygen upto 150 miles in altitude, red when electrons interact with oxygen above 150 miles, blue when they interact with nitrogen upto 60 miles and purple when they encounter nitrogen beyond 60 miles.
But then how do we see the lights dance? All these magnetic and electrical forces constantly react with each other in changing combinations and this causes the auroras to dance! Also more pertinent to what we learnt in class, green, red, blue and purple aren’t the only colors we can see in an aurora borealis. These different colors all blend together due to the constantly shifting magnetic and electric forces and we see a plethora of different colors based on which colors combine and in what ratio!
I am intrigued to be introduced to new concepts related to light so that I can continue to explore such similar topics that I am curious to learn about.
I’m interested in learning why this phenomenon only occurs at certain times of the year. Would that depend on the levels of oxygen in the atmosphere?
Cool! Why does the altitude of the meeting change the color?
This reminds me of the longer video posted in the assignment page. Starting around 14 min 20s, the teacher excites different gases and they glow red, green, blue.