Aurora displayed in northern latitudes is called aurora borealis. An Auroras is a natural light mostly seen in the high latitude regions and within the aurora oval may be directly overhead. It is caused by charged particles such as electrons and protons, entering the atmosphere from above causing ionization and excitation of atmospheric constituents, and consequent optical emissions. When sun rises from an unusual direction, greenish or faint glow would come from father away and illuminate the pole ward horizon. And it was occasionally seen when large geomagnetic storms temporarily enlarges the aurora oval. (Stamper and Lockwood, 1999)

The most common color of auroras are red, green, blue, yellow and pink are mixed by red and green or blue. When the solar activities get stronger, low concentration of atoms and lower sensitivity of eyes at this wavelength make faint red color visible. Green aurora happens when there is a high concentration of atomic oxygen and higher eye sensitivity. The wavelength of blue aurora is radiates in both red and blue parts of the spectrum when ionized molecular nitrogen dominated in producing visible light emission.

So far, the physical processes which lead to various type of auroras is not fully realized, but one reason might be the interaction of the solar wind with earth’s magnetosphere. And it can be also cause by particles trapped in the radiation belts to precipitate into the atmosphere. (wikipedia).

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