Data collected from two NASA spacecraft have revealed that Earth's northern and southern auroras are not simply mirror images of one another, as previously believed.

Nearly circular bands, called auroral ovals, surround both poles of our planet. They result from the interaction between Earth's magnetic field, or magnetosphere, and energized particles from the solar wind that emit light in the upper atmosphere. A research team led by Timothy J. Stubbs of NASA's Goddard Space Flight Center analyzed images from NASA's Polar spacecraft and the IMAGE spacecraft taken of both the northern (aurora borealis) and southern (aurora australis) lights. "This is the first analysis to use simultaneous observations of the whole aurora in both the Northern and Southern hemispheres to track their locations," Stubbs remarks.

During the study period, the researchers noted that the auroras tilted and changed based on how the planet's magnetic field is oriented toward the sun. "Because Earth's magnetic field is not a perfect dipole," Stubbs says, "we think this fact plays some role in causing the auroras to not be mirror images of each other."