7/28/2019 Aurora the Northern Lights 111209
This is why there is a difference in colors, according to the altitude.At a higher altitude, oxygen red dominates then oxygen green and nitrogen blue/red, then finallynitrogen blue/red when collisions stop oxygen from emitting anything.
So, in short:When electrically charged particles from the Sun collide with the Earth's upper atmosphere, theycause the atmospheric atoms and ions to radiate different colors and bands of light.
How are the colors of the Aurora formed?
The colors of the Aurora depend on the gases in the Earths Atmosphere and the solar particlesthat are colliding with the different gases at the various heights.
At a very high altitude, oxygen is the most common gas, and collisions there can create a rarered aurora.
At lower altitudes, collision with oxygen here makes a yellow-to-green light that is commonlyseen.
At about 60 miles up, the nitrogen molecules creates a red light that often seems to form thelower fringes of what can be called the auroral curtains.
There are lighter gases high in the atmosphere, like hydrogen and helium, which makes the blueand purple colors, but we cant always really see them in the night sky.