The Southern Lights glow blue and purple when high-energy solar particles collide with nitrogen in Earth's atmosphere.

Auroras, known as the Aurora Australis in the Southern Hemisphere, occur when charged particles from the solar wind collide with gases in Earth's thermosphere. Most auroras appear green because the human eye is most sensitive to the 557.7 nanometer wavelength emitted by excited oxygen atoms. Blue and purple colors are much rarer because they require the ionization of molecular nitrogen (N2 and N2+).Nitrogen molecules require significantly more kinetic energy to excite than oxygen. This usually happens during periods of high solar activity, such as Coronal Mass Ejections (CMEs), which send bursts of high-velocity particles toward Earth. According to NASA, these nitrogen emissions occur at lower altitudes, typically between 80 and 100 kilometers (50 to 60 miles) above the surface.The specific blue light is emitted at a wavelength of 427.8 nanometers. Because the human eye has low sensitivity to the blue-violet end of the spectrum, these colors often appear as a faint grey or white to the naked eye. However, modern digital sensors can accumulate light over several seconds to reveal the true, vibrant saturation of the nitrogen-induced purple fringe.Research from the University of Alaska Fairbanks Geophysical Institute confirms that the intensity of these colors serves as a visual indicator of the solar wind's power. During the historic Carrington Event of 1859, observers reported seeing diverse colors across the sky due to the extreme energy levels. Today, scientists use these color variations to map the composition and density of the upper atmosphere.