In northern latitudes, the effect is known as the aurora borealis (or the northern lights), named after the Roman goddess of dawn, Aurora, and the Greek name for the north wind, Boreas, by Galileo in 1619. The aurora can be seen best at this time, which is called magnetic midnight. The instantaneous distribution of auroras ("auroral oval") is slightly different, being centered about 3–5 degrees nightward of the magnetic pole, so that auroral arcs reach furthest toward the equator when the magnetic pole in question is in between the observer and the Sun. It was hardly ever seen near the geographic pole, which is about 2000 km away from the magnetic pole. Tromholt (1882) in more detail, established that the aurora appeared mainly in the "auroral zone", a ring-shaped region with a radius of approximately 2500 km around the Earth's magnetic pole. Elias Loomis (1860), and later Hermann Fritz (1881) and S. Early evidence for a geomagnetic connection comes from the statistics of auroral observations. A geomagnetic storm causes the auroral ovals (north and south) to expand, and bring the aurora to lower latitudes. Day-to-day positions of the auroral ovals are posted on the internet. A region that currently displays an aurora is called the auroral oval, a band displaced towards the nightside of the Earth. Most auroras occur in a band known as the auroral zone, which is typically 3° to 6° wide in latitude and between 10° and 20° from the geomagnetic poles at all local times (or longitudes), most clearly seen at night against a dark sky. 6 Historical theories, superstition and mythology.5 Auroral events of historical significance.3 Interaction of the solar wind with Earth.Different aspects of an aurora are elaborated in various sections below. Proton auroras are usually observed at lower latitudes. Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere. 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. The resulting ionization and excitation of atmospheric constituents emits light of varying colour and complexity. 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. Images of the aurora australis and aurora borealis from around the world, including those with rarer red and blue lightsĪn 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.
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