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Awesome Spate of Auroras this Week

January 13, 2011

Space Weather reports this week: An active region on the far side of the sun erupted this morning, hurling a bright CME into space. The Solar and Heliospheric Observatory (SOHO) saw the cloud emerging over the sun’s eastern limb. This week, auroras around the Arctic Circle have been so bright, even clouds and glaring moonlight could not spoil the show. Aurora gallery of photos, click here.

What causes the Aurora?

The energy source for the aurora is 149 million kilometers (km) (93 million miles) from Earth at the sun. The sun continuously emits charged particles (mostly protons and electrons), which are the byproducts of thermonuclear reactions occurring inside the sun. These charged particles make up the solar wind, which travels away from the sun through space at speeds ranging from 300 to 1,000 km/sec.—about a million miles per hour. Traveling at this high speed, the solar particles can reach the Earth in two to three days.

At Earth, the steady solar wind is deflected by Earth’s magnetic field, or magnetosphere. The solar wind flows around the magnetosphere much like a river flows around a stone. It also pushes on the magnetosphere and distorts it so that instead of a symmetric set of magnetic field lines—like one might have around a bar magnet—the magnetosphere is stretched and elongated into a comet shape with a long tail trailing away from Earth on the side away from the sun.

When there is a disturbance on the sun, such as a solar flare or coronal mass ejection, it can produce a disturbance in the solar wind. This in turn will cause a disturbance in the balance between the solar wind and Earth’s magnetic field. As a result, electrons and protons are accelerated within the magnetosphere. These charged particles are constrained to the magnetic field lines much like beads on a wire. The accelerated particles will travel down the magnetic field lines of Earth and collide with the atoms and molecules of the upper atmosphere where the magnetic field lines reach down to surface of the Earth near the north and south magnetic poles.

When the particles from the magnetosphere collide with the atoms and molecules of the atmosphere, the particle’s energy can be transferred to the atoms and molecules (typically O, N, and N2) of the atmosphere forming excited states of O, N and N2. When these finally release their energy and return to their normal ground state, they give up energy in the form of light. This is the light that we see from the ground as an aurora.

Source: Earth Portal

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