Purple Rain: Colors of the Northern Lights

Purple Aurora

Isle Royale Aurora, photo by Ross Ellet

Music is music, ultimately. If it makes you feel good, cool.
~Prince

Prince was a musician who had a huge effect on my life. I went to school near Minneapolis when he was transforming music through his own work and what he did with a host of artists. I’m very sad at his passing. Down at the bottom I have one of my favorite clips of Prince.

I’ve been lucky enough to see the northern lights dozens of times but have probably only seen purple auroras three or four times. Causes of Color explains the colors of the northern lights:

The sun radiates all visible colors, which is why sunlight appears white. The spectrum of visible light associated with the aurora is much more restricted. The aurora is caused by charged particles in the solar wind colliding with atmospheric atoms and ions. The collisions cause the electrons of the atmospheric atoms to become excited. As the electrons return to their original energy levels, these atoms emit visible light of distinct wavelengths, to create the colors of the display we see.

The color of the aurora depends on the wavelength of the light emitted. This is determined by the specific atmospheric gas and its electrical state, and the energy of the particle that hits the atmospheric gas. The atmosphere consists mainly of nitrogen and oxygen, which emit the characteristic colors of their respective line spectra. Atomic oxygen is responsible for the two main colors of green (wavelength of 557.7 nm) and red (630.0 nm). Nitrogen causes blue and deep red hues.

Most of the auroral features are greenish-yellow, but sometimes the tall rays will turn red at their tops and along their lower edges. On rare occasions, sunlight will hit the top part of the auroral rays to create a faint blue color. On very rare occasions (once every 10 years or so) the aurora can be a deep blood red color from top to bottom. Pink hues may also be seen in the lower area of the aurora. In addition to producing light, the energetic auroral collisions transmit heat. The heat is dissipated by infrared radiation, or transported away by strong winds in the upper atmosphere.

Read on for more and also check out more about the Northern Lights on Michigan in Pictures.

Ross took this on August 10th last summer. He says “The Northern Lights over Moskey Basin in Isle Royale National Park. This is the first time in my life I have seen a bright purple aurora develop.

View his photo background bigilicious and see more in his Aurora slideshow.

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