What causes the Northern Lights?

What is a eruption of gas in the sun that causes the northern lights?

• Answer:

  A "CME" or "Coronal Mass Ejection". If aimed even roughly in the direction of the Earth, the interaction between the charged particles in the CME and the Earth's magnetic field can cause spectacular auroras. That would be a SOLAR FLARE. Solar Flares are eruptions of superheated, ionized gas which may hit the Earth. The magnetic field surrounding the Earth acts as a sort of shield against these flares, and when the flares hit this field, incredible light shows are created that you can see at the Northern and Southern lights. I think the aurorae happen due to radiation interacting with the ionosphere.