Why are the northern lights different colors?
The color of the aurora depends on which chemicals are present and the altitude of the meeting of atoms and particles.
- The most frequent colour seen is green, caused by oxygen typically around 100 km high
- Red is more rare and harder to see, also caused by oxygen and higher altitudes (between 200-400 km).
- The purple and blue colors are caused by ionised nitrogen and occur at much lower altitudes.
- If all the colors mix together they appear as white (or if the lights are very dim).
Displays can vary in intensity – from a glowing curtain of greenish yellow lights, dancing in the distance to a spectacular, multi-colored fusion stretching across the sky. Most people lucky enough to see the aurora witness a display of green lights but if you are really lucky then that display might be yellow and red, or even multi-colored.
The differences depend on two main factors: what type of gas is reacting with the solar particles and at what altitude this activity is taking place. Most of it occurs 100-200 km above the Earth – a level where ‘excited’ nitrogen atoms glow green and blue. And above 200 km, oxygen atoms glow red when reacting with charged particles from the sun.
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