A glow in the ionosphere of a planet or moon caused by the interaction between the object's magnetic field and charged particles from the Sun; “aurora” is Latin for “dawn.” Aurorae have been observed on Earth, Jupiter, Saturn, Mercury, and Uranus, and are expected to occur in some form on all worlds that have magnetospheres. They are distinguished from airglow by their confinement to magnetic polar and subpolar regions, and their sporadic occurrence. Different auroral colors stem from emission by different atmospheric gases. On Earth, the northern and hemisphere versions are known as aurora borealis and aurora australis, respectively. Aurorae change in brightness, shape, color, dynamics, and location in response to changes in the state of the magnetosphere. This variability shows up most dramatically during an auroral substorm.
