Question: What forms the Aurora?

Christian Wirtz answered on 18 Nov 2013:

Hi Grace,

this is a really good question! I’ve only once had the pleasure of seeing the Aurora Borealis but that time was beautiful!

To have any chance of getting an aurora we need a solar flare that travels in the direction of earth. A solar flare is an ejection of huge amounts of energy and particles from the sun. It takes about two days for these particles to reach us. Our fastest satellites would take about 35 days to reach the sun, so you can imagine how fast this material is traveling!
Some of these particles are negatively charged electrons or positively charged ions. When they hit the earth’s magnetic field, these charged particles are deflected and flow along the earths magnetic field lines and are all pushed into the atmosphere above the poles (depending on their charge they will go either to the north- or the south pole). That is because the magnetic field lines enter the earth there and the field is weak near the poles.
There the particles interact with the atoms and molecules in our atmosphere, mostly the nitrogen, but also the oxygen. They pass their energy onto these molecules which produces fluorescence, the same effect you get when using a UV-light (you may know this as a black light). Depending on the amount of energy of the particles arriving at earth and how deep they penetrate into our atmosphere, you get different colours and shapes. Most common is the green aurora but you can also have red or violet ones or combinations of the three.
I’ve only once seen a green one that looked like a curtain when I was in the north of Sweden but it was stunning!

If you want to observe the aurora this year is actually not too bad. The sun goes through (approximately) 11 year cycles of much and no activity, which determines the amount of solar flares. When I was in Sweden in 2009 it was at a minimum so next year or the year after it should be at a maximum which lots of beautiful auroras!