The scientific understanding of the aurora began in the late 1800s with the advent of spectroscopy, the study of light's color spectrum. Through spectroscopy, the light of the aurora was found to originate in the Earth's upper atmosphere, rather than a reflection or refraction of sunlight, as had commonly been believed. The red color of the aurora was measured at 630 nanometers. In the 1900s, scientists found that particular atoms and molecules emit such precise colors in the rarefied air of the upper atmosphere. With the dawn of the space age, scientists discovered that the bombardment of solar particles energizes atmospheric atoms and molecules.
Most auroral light comes from oxygen atoms and nitrogen molecules.
At the extremely low-air densities between roughly 60 miles and 155 miles high, oxygen atoms emit predominantly green light, the most common color of the aurora. In the even more rarefied air above 155 miles, oxygen atoms emit predominantly red light. The red and green aurora are often seen together, with the red situated on top like a crown. The solar max is now peaking, and will until 2001. Based upon this prediction, several large solar flares over the next three or four years can be expected, which will trigger major space storms.