Last Thursday,January 9th 2014, a strong sun storm sent charged solar particles flying through space. Eventually these particles collided with Earth's magnetic field and atmosphere. The collision of these particles, and atoms in Earth's atmosphere are what put on the fantastic show commonly known as the Northern Lights.
Last Thursday the light show was visible as far south as Calgary, Canada and the lower 48 states due an increased exposure of plasma from the sun, known as a coronal mass ejection. They are commonly associated with solar flares. Basically what happens is that storms on the sun send these charged particles flying through space. When they start to get closer to Earth, they follow Earth's magnetic field and float closer to the poles. This explains why the Northern Lights are more commonly seen closer to the poles. Now you may be wondering, what causes the spectacular light show?
This is a concept that may take you back to an undergraduate Chemistry class. When charged solar particles collide with atoms in Earth's atmosphere they become "excited", so excited that they light up in different colors according to what gas they are reacting with. During collision, electrons around the nucleus will move to higher energy orbits farther away from the nucleus. Eventually the electron will move back down to a lower energy orbit and release a photon-a particle of light! Oxygen molecules tend to let off green light, while hydrogen and nitrogen light up red and blue.