Aurora Borealis

An aurora, also commonly known as the polar lights, is a natural light display in Earth's sky, predominantly seen in high-latitude regions. Auroras display dynamic patterns of brilliant lights that appear as curtains, rays, spirals, or dynamic flickers covering the entire sky. November through to February offer the darkest skies and longer evenings for maximum sky-gazing. The strongest lights tend to appear between 9pm and 2am, though the best sightings often occur between 11pm and midnight. The light show we see from the ground is caused by electrically charged particles from space entering the Earth's upper atmosphere at a very high speed. These particles originate from our star - the sun. Auroras are the result of disturbances in the magnetosphere caused by the solar wind. Major disturbances result from enhancements in the speed of the solar wind from coronal holes and coronal mass ejections. These disturbances alter the trajectories of charged particles in the magnetospheric plasma. These particles, mainly electrons and protons, precipitate into the upper atmosphere (thermosphere/exosphere). The resulting ionization and excitation of atmospheric constituents emit 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. aurora is called the "auroral oval", a band displaced by the solar wind towards the night side of Earth. Early evidence for a geomagnetic connection comes from the statistics of auroral observations. Elias Loomis and later Hermann Fritz and Sophus Tromholt in more detail, established that the aurora appeared mainly in the auroral zone.

In northern latitudes, the effect is known as the aurora borealis or the northern lights. The former term was coined by Galileo in 1619, from the Roman goddess of the dawn and the Greek name for the north wind.. The southern counterpart, the aurora australis or the southern lights, has features almost identical to the aurora borealis and changes simultaneously with changes in the northern auroral zone.[13] The aurora australis is visible from high southern latitudes in Antarctica, Chile, Argentina, South Africa, New Zealand and Australia. The aurora borealis is visible from being close to the center of the Arctic Circle such as Alaska, the Canadian Territories, Iceland, Greenland, Norway, Sweden, Finland and Russia. On rare occasions the aurora borealis can be seen further south, for example in Estonia, Latvia, Lithuania, Scotland, Ireland, Denmark, and the northern part of the contiguous United States.

A geomagnetic storm causes the auroral ovals (north and south) to expand, bringing the aurora to lower latitudes. The instantaneous distribution of auroras ("auroral oval")[6] is slightly different, being centered about 3–5° 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. The aurora can be seen best at this time, which is called magnetic midnight.

Auroras seen within the auroral oval may be directly overhead, but from farther away, they illuminate the poleward horizon as a greenish glow, or sometimes a faint red, as if the Sun were rising from an unusual direction. Auroras also occur poleward of the auroral zone as either diffuse patches or arcs, which can be subvisual.