our atmosphere: perfectly imperfect

The Northern Lights are an interaction between our atmosphere and energetic particles from the sun. In a process which takes several days, particles that were shot out from the sun travel to earth and are attracted to the Northernmost and Southernmost poles due to the pull of  Earth's magnetic field on these charged particles. These charged particles are what create these amazing shows of light at out poles. According to Physics.org:

The Earth’s magnetic field traps parts of the solar wind as it passes the planet, and the electrons and ions that make up that wind travel towards the Earth’s magnetic poles. Molecules and atoms in the Earth’s upper atmosphere are left ionized or excited by collisions with the particles from the solar wind, and in either regaining an electron or returning to their ground state, they emit light – the glow of the aurora.

                                                                                                                 These entrancing lights also have an effect on our atmosphere. The law of Conservation of Energy states that energy cannot be created nor destroyed. What does this mean for us? All the energy that enters our atmosphere (a closed system) is still in our atmosphere in one form or another. For our average light show, this doesn't mean too much. Yes, the energy from the sun that was contained in these particles is now in our atmosphere in the form of light and heat, but, according to the UAF Aurora Forcast, "[S]ince the aurora takes place at about 90 – 100 kilometers (55.2 – 62.3 miles) altitude, only the atmosphere at or above that height is affected by aurora (auroraforecast.gi.alaska.edu/faq.php#environment)." However, geomagnetic storms aren't your average light show. These storms, due to the high influx of particles, effects of solar wind and other particular circumstances, have a strong effect on our atmosphere, even causing changes in the rotation of  satellites. Learn more about geomagnetic storms here.

Thus, through an influx of energy into our atmosphere and magnetic field, the northern lights appear. This sounds pretty magical, and it is. As these particles from the sun interact with the gases in our atmosphere, the gasses begin emitting their excess energy in the form of light. According to as student at Oregon State University, "When charged particles from the sun hit particles of these atmospheric gasses, they ionize or excite the gas particles and cause them to glow and their return to ground state is what emits the aurorae.  The green aurorae are produced from a reaction of solar particles with oxygen at altitudes of up to 150 miles . . .  " (physics.oregonstate.edu/~giebultt/COURSES/ph313/Extermpap2.pdf). Learn more about the colors of the Aurora and why green is the most common here.