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 indicate that auroral phenomena occur in its polar regions. Images of Saturn aurora show a very active pulsating pattern. 一颗极地卫星拍摄到了地球南极为中心的极光图像。木星的紫外照片表明，极光现象出现在其极地区域。土星的极光图像显示出了非常活跃的脉动模式。

This sketch of charged particles spiraling around magnetic field lines is conceptual only. It does offer an impression of how the magnetic field of the Earth helps to protect us from the ionizing radiation of particles from the solar wind. 这张描绘带电粒子沿磁场线螺旋运动的示意图只是概念性的。它确实能给我们一个印象，即地球的磁场如何帮助我们抵御来自日冕物质抛射的离子辐射。

Jupiter Aurora

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.

Aurora at Earth's South Pole

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

From space, the aurora is a crown of light that circles each of Earth's poles. The IMAGE satellite captured this view of the aurora australis (southern lights) on September 11, 2005, four days after a record-setting solar flare sent plasma-an ionized gas of protons and electrons-flying towards the Earth. The ring of light that the solar storm generated over Antarctica glows green in the ultraviolet part of the spectrum, shown in this image. The IMAGE observations of the aurora are overlaid onto NASA's satellite-based Blue Marble image. From the Earth's surface, the ring would appear as a curtain of light shimmering across the night sky.

Though scientists knew that the aurora were caused by charged particles from the Sun and their interaction with the Earth's magnetic field, they had no way to measure the interaction until NASA launched the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite in 2000. The satellite's mission was to collect data that would allow scientists to study the structure and dynamics of the Earth's magnetic field for the first time. Designed to operate for two years, IMAGE sent its last data to Earth in December 2005 after a highly successful five-year mission.

Since 2000, IMAGE has provided insight into how the Earth's powerful magnetic field protects the planet from solar winds. Without the shield the magnetic field provides, the upper atmosphere would evaporate into space under the influence of solar winds. IMAGE has shown scientists what sort of changes the magnetic field undertakes as it diverts solar winds from the Earth. Image and description courtesy NASA