Beautiful lights sometimes seen in the night sky in northern and southern regions of the Earth are caused by the interaction of the solar wind - a stream of charged particles escaping the Sun - and our planet's magnetic field and atmosphere.
The Earth's magnetic field traps some of the particles and sends them on a collision course with molecules in the atmosphere. As a result of these repeated, tiny crashes, energy is released in the form of light.
Photo: Saturn's aurora taken by the Hubble Space Telescope (NASA, ESA, J. Clarke and G. Bacon)
The solar wind's assault on the Earth can be easily seen.
Brian Cox travels to Norway to see the Northern Lights.
Professor Brian Cox travels to Norway in search of the Aurora Borealis, or Northern Lights. Astrophysicist Professor Mike Lockwood accompanies him as they wait for the dazzling display brought by the solar wind.
A stream of particles from the Sun stretches beyond the outer planets.
Measurements made by the 1962 Mariner 2 spacecraft confirmed the presence of solar wind, a stream of particles from the Sun that stretches far beyond the outer planets. The Earth's magnetic field fights a constant battle against the solar wind's atmosphere eroding effects.
An aurora, sometimes referred to as a polar light, is a natural light display in the sky, predominantly seen in the high latitude (Arctic and Antarctic) regions.[a] Auroras are produced when the magnetosphere is sufficiently disturbed by the solar wind that the trajectories of charged particles in both solar wind and magnetospheric plasma, mainly in the form of electrons and protons, precipitate them into the upper atmosphere (thermosphere/exosphere), where their energy is lost. The resulting ionization and excitation of atmospheric constituents emits light of varying colour and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere. Proton auroras are usually observed at lower latitudes. Different aspects of an aurora are elaborated in various sections below.