Untitled DocumentA quick guide to common space weather terms:
Aurora: Sheets and waves of vibrant light caused by charged solar particles igniting gases in Earth's atmosphere. They are typically visible at northern latitudes, and sometimes (during heavy solar activity) into the mid-latitudes of the United States and elsewhere. In-depth look at the aurora
Corona: The Sun's outer atmosphere. Because it is surprisingly hot, typically reaching 2 million degrees, the atmosphere emits energy in extreme ultraviolet light and X-rays. These are blocked by the Earth's atmosphere and can be seen only in space. More about the Sun and its energy
Coronal hole: A hole in the Sun's atmosphere, which show up as a dark area. Holes are associated with open magnetic field lines. Researchers say high-speed solar winds originate in these holes.
Coronal mass ejection (CME): A bubble of gas and charged particles, similar to a solar flare, ejected from the Sun over several hours.
Geomagnetic storm: When unusually strong surges of solar wind (charged particles from the Sun) hit the Earth. This effect causes variations in the magnetic field which surrounds the Earth. The result are visible aurora (Northern and Southern lights).
Heliosphere: Charged particles streaming away from the Sun envelop Earth and the other planets in a magnetic bubble. "The heliosphere is the bubble this solar wind blows out into the local interstellar medium. It defines the volume of space over which our Sun's influence predominates," says Richard Marsden, the ESA's Ulysses project scientist.
The closest boundary of the heliosphere is thought to extend about 100 AU out from the Sun, which is 100 times the distance of the Earth from the Sun. The heliosphere protects us from the worst space weather -- cosmic rays. These very energetic particles are generated far away in the universe, and if not for our protective bubble, they would bombard Earth continuously and damage living cells. "Without the heliosphere, life would certainly have evolved differently - and maybe not at all," Marsden says. The heliosphere is shaped and recharged by the solar wind.
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Hot plasma trapped in magnetic loops.
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Magnetic activity on the Sun: The Sun rotates around its axis in about four weeks, but various zones and layers turn at different rates -- from 25 to 35 days for a rotation. The resulting shear (the difference in speed between adjacent regions) twists and intensifies magnetic fields.
Giant loops of hot plasma, contained by the magnetic fields, lift off the Sun's surface. When the arching magnetic field lines clash, the result is a magnetic explosion in the Sun's atmosphere. The largest of these events produce an intense solar flare and/or a coronal mass ejection of gas into the solar system. Minor explosions and mass ejections occur daily. A non-stop solar wind consisting of electrons and charged atoms travels past the Earth and far beyond the outermost planets.
Solar flare: The Sun frequently spews plumes of energy that are more energetic than the constant solar wind. These solar flares contain gamma rays and X-rays, plus energized particles (protons and electrons). Energy can be equal to a billion megatons of TNT is released in a matter of minutes. Flare activity picks up as sunspots increase.
The magnetic explosion during a solar flare accelerates electrons and atomic nuclei to significant fractions of the speed of light. Unlike much slower atomic particles in the solar wind, which travel straight out from the Sun, the energetic particles from a flare follow curved lines of the Sun's interplanetary magnetic field. The particles slant in toward Earth from the west at about 45 degrees to the direction of the Sun.
Solar flare classification: Solar flares are classified based on their output of X-ray energy at the peak of their burst.
Solar wind: Charged particles, mostly protons and electrons, streaming out from the Sun. Earth's own protective magnetic field repels most of the solar wind. This stream of outflowing particles comes in two varieties, "fast" (about 750 km/s) and "slow" (350 to 400 km/s).
Solar wind speed varies with solar latitude and solar activity. During periods of low activity, the fast wind emanates from the poles and the slow wind from near the equator. The fast wind comes from relatively cool gaps in the corona, called coronal holes, and the slow wind from hotter coronal "streamers". The solar wind feeds the Sun's heliosphere.
Sunspots: Magnetic fields within the Sun slow down the radiation of heat in some areas, causing sunspots, which are cool areas and appear as dark patches. Although flares and mass ejections can occur at any time, the Sun is stormiest when sunspots are most numerous. Scientists are not sure why they occur, nor why the duration and intensity of sunspot cycles varies greatly.
Sunspot cycle: Sunspot activity peaks every 11 years. A peak occurs during the year 2000. During peaks, the Sun experiences more flares and eruptions, and sends more energy toward Earth. Therefore, the aurora are more spectacular, satellites can be threatened, and communications blackouts sometimes occur. More
SOURCES: ESA, NASA, SPACE.com reporting
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