Aurora

When energetic charged particles enter the earth's atmosphere from the solar wind, they tend to be channeled toward the poles by the magnetic force which causes them to spiral around the magnetic field lines of the earth. They are energetic enough to ionize air molecules, so a considerable number of atoms and molecules are elevated to excited states. When they make the transition back to their ground states they emit light characteristic of the atoms and molecules. Red and green light emitted from oxygen atoms is a constituent of the light seen at the poles. Atmospheric nitrogen also plays a role. An example of the colors that might be visible can be found by observing the nitrogen spectrum. Near the north pole the light show is called the aurora borealis and near the south pole it is called aurora australis.

A polar satellite captured images of aurora over the South Pole of the Earth. UV photographs of Jupiter indicatethat auroral phenomena occur in itspolar regions. Images of Saturn aurora show a very active pulsating pattern.

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Jupiter Aurora

NASA image taken by Hubble Space Telescope's STIS on November 26, 1998

Like the aurora near the Earth's poles, the glowing display near Jupiter's poles comes from the interaction of charged particles with the planet's magnetic field, which is more intense near the poles. Jupiter's aurora show the distinct magnetic footprints of three of Jupiter's larger moons: Io, Europa and Ganymede. The luminous path at extreme left if from Io and the one near the center from Ganymede. The path below and to the right of Ganymede's trail is from Europa. The strong electrical and magnetic interactions of these moons with Jupiter has been a subject of intense study.

This image was taken in the ultraviolet region of the electromagnetic spectrum.

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Aurora at South Pole

NASA image taken by Polar satellite, November 2004

The Sun produced at least five major "halo" coronal mass ejections (CMEs) over the period of Nov. 4-8, 2004, an unusually fast pace for solar activity.The Polar spacecraft saw the aurora australis (southern lights) expanding and brightening on Nov. 8. A "halo" CME occurs when a CME produces an expanding circle of particles all around the Sun. When observers see this they know the CME is heading directly towards or away from Earth. In this case, all were headed in our direction, bringing the auroral light show with them. The source of storms was a group of sunspots called Active Region 696. The area also produced powerful solar explosions called flares.

Credit: NASA/UC Berkeley

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