A light in the darkness. 💡 This time of year, most of the Southern Hemisphere is bathed in hours of winter darkness, but last week the aurora australis (or Southern Lights) faintly lit the night sky several times. The Visible Infrared Imaging Radiometer Suite (VIIRS) on the NASA-NOAA Suomi NPP satellite detects this nighttime light in a range of wavelengths from green to near-infrared and uses filtering techniques to observe signals like city lights, auroras, and reflected moonlight. When fast-moving electrons from space collide with oxygen and nitrogen molecules in the ionosphere, they become chemically excited. As the gases return to their normal state, they emit small bursts of energy in the form of light (photons). Oxygen molecules and atoms usually glow green, white, or red, while nitrogen tends to be blue or purple. This ghostly light—aurora—originates at altitudes of 100 to 400 kilometers (60 to 250 miles). As Solar Cycle 25 continues, more sunspots and solar storms are emer...