Aurorae - Northern Lights

picture Aurora polaris (ger: Polarlicht; fr: aurore polaire)

Aurora is latin for 'dawn'. The Northern Lights and the aurora borealis are two names for the same thing. The term aurora borealis was introduced by Galileo Galilei in 1619 who wrongly thought that the aurora is caused by sunlight reflecting from the high atmosphere. However, from thereafter the name was used for Northern Lights. The proper name for the aurora of the southern hemisphere is the aurora australis. Together the aurora australis and the aurora borealis are known as the aurora polaris. Nowadays the simple name aurora is mostly used, as is the name Northern Lights.

picture In fact, the aurora is a luminous phenomenon occuring in the upper atmosphere at altitudes between about 100km and 1000km. Auroras are visible best from the auroral zone the region about 15-30 degrees from each magnetic pole with the greatest frequency of aurorae. The region within which auroral activity occurs is the auroral oval and is only visible from space. The center of the auroral oval lies at the geomagnetic poles - not to be confused with the geographic poles.

picture However, infrequently they might be seen as far down as the equator. Like giant curtains in the sky that slowly wave as if a gentle breeze were blowing, aurorae fill the entire sky with changing colours and motion and no two aurorae are ever alike. An auroral display may begin with a faint glow, an overall veil, or weak patches in the sky towards the pole. Eventually it will form an arc and may develop rays. Their intensity may vary, multiple bands are likely to form flickering and flaming in surges of brightness across the sky.

What Makes Northern Lights Happen? Click here.

Is Earth the only planet with aurorae?

Clearly no! Every rotating planet with a magnetosphere - or magnetic field should have aurorae. The proof has been given by the famous Hubble telescope in 1996 when it took breath-taking images of a Jupiter aurora. For it's lack of a magnetic field o ur Moon does not display aurorae - what a pity!.

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