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Auroras, Why Are They Green?

June 25, 2010

What you see here is the amazing image of Aurora (aurora australis to be specific or southern lights) taken by astronauts onboard International Space Center.  Isnt’t it beautiful! Auroras are result of the interaction between ions and electrons from the solar wind with Earth’s magnetic field and upper atmosphere. During Coronal Mass Ejections from the sun, high energetic ions are bombarded towards the earth. These ions migrate towards poles due to Earth’s magnetic fields, that’s why this phenomenon is seen mostly at Northern and Southern poles of the earth. These high energetic ions interact with Oxygen and Nitrogen of the upper atmosphere and excite them to higher energy levels. When the atoms fallback to ground state it emits light typical to particular atom. Oxygen emits at a wavelength of 558 nm (green) and at 630 nm (red ). Emission at 558 nm is more prominent and that’s how Aurora gets it’s greenish color. A slight tinge of red color can also be seen at lower left corner of the image.  Auroras in other colors have also been seen such as blue and purple but green ones are most prominent. Also, seen in the image is earth’s horizon, the limb, and the upper atmosphere (shown in blue).

This particular Aurora image is a result of a recent  coronal mass ejection activity in the sun which occurred during May 24, 2010. Our Sun has been surprisingly low in activity this year and scientists are puzzled as to what is happening to Sun. But there was some activity this month when four such mass coronal ejections occurred during May 22-May 24, 2010.  Here is the image of one such activity recorded during this period by NASA’s SOHO mission.  In the image, you can see the loop which is the mass of charged particles coming out of the sun’s surface; a disc has been used to cover the sun so that to get better image of the corona. The size and location of the sun’s surface  is indicated by the white circle. Truly amazing images and amazing phenomena. I will try to write in detail more about sun’s activity and it’s impact on earth sometime next week.

Photo credit: NASA Earth Observatory

Filed under: Science

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2 Comments Leave a Comment

  • 1. Science Is Beautiful &raq&hellip  |  January 24, 2011 at 5:32 pm

    […] photographed by Tor Even Mathisen. It’s just spectacular. As described in my earlier posts (here and here), when high energetic ions ejected from sun interact with our atmosphere, they energize […]

  • 2. Science Is Beautiful &raq&hellip  |  March 27, 2011 at 2:30 pm

    […] create a breathtaking time-lapse video for us to enjoy and cherish. You can read my earlier posts (here and here) to understand the science behind the origin of green and violet colors as seen in Aurora […]

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