The Northern Lights, or Aurora Borealis, are one of Earth’s most breathtaking natural light displays, painting the polar night sky with shimmering curtains of color. This spectacle is the visual result of charged particles, primarily electrons and protons from the sun, being funneled by Earth’s magnetic field toward the poles. There, they collide with atmospheric gases. We can explore three fascinating facts that reveal the physics and cosmic context of this geomagnetic light show.
The Aurora Can Make Sound
Reports from high-latitude residents of crackling or hissing noises accompanying bright auroras have been validated by modern research. Scientists confirmed that an audible sound can be produced during intense auroral displays, although the mechanism is not the light itself. The visible aurora occurs at altitudes of 100 kilometers or more, which is too far for sound to travel to the ground instantaneously.
The noise, described as a faint clap, crackle, or static-like hiss, originates much closer to the observer, approximately 70 meters above the ground. This phenomenon is linked to a temperature inversion layer, where warm air traps colder air near the surface, allowing static electrical charge to accumulate. The electromagnetic disturbance created by the distant aurora triggers a rapid discharge of this static charge, generating the nearly instantaneous, audible sound.
What Causes the Different Colors
The aurora’s vivid palette is a direct consequence of the atmospheric gases being struck by solar particles and the altitude at which these collisions occur. The most common color, a vibrant green, is produced when incoming electrons excite oxygen atoms, typically between 100 and 300 kilometers above the surface. At much higher altitudes, above 200 kilometers, the oxygen atoms release energy at a longer wavelength, resulting in a rare, deep red color that often appears along the top edge of the display.
Nitrogen molecules are responsible for the blue, purple, and pink hues that sometimes appear in the lower sections of the aurora, usually around 100 kilometers or less. Collisions with nitrogen emit light in the blue spectrum, and when mixed with the common green of oxygen, the resulting light can create a pink or magenta fringe at the bottom edge of the curtains. The specific color acts as a physical indicator of both the gas involved and the height of the energy release.
Auroras Happen on Other Planets
The aurora is a universal process that occurs on any planet possessing both an atmosphere and a sufficiently strong magnetic field. Extraterrestrial auroras are often observed on the gas giants, Jupiter and Saturn, which boast magnetic fields far more powerful than our own planet. Jupiter’s magnetic field, for instance, is approximately 20,000 times stronger than Earth’s, driving auroras that are immensely larger and more energetic, and are primarily visible in ultraviolet light.
Like Earth, these planetary light shows occur in ring-shaped regions around the magnetic poles, known as the auroral oval. On Jupiter, the energy for the aurora comes not only from the solar wind but also from charged particles originating from its volcanically active moon, Io. Even planets like Mars, which lack a global magnetic field, can exhibit auroras where localized pockets of crustal magnetism interact with the solar wind.