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Active Regions, CMEs, and X-
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| Title |
Active Regions, CMEs, and X-Class Flares |
| Explanation |
Space Weather forcasters [ http://sec.noaa.gov/today.html ] are predicting major storm conditions over the next few days as the active Sun [ http://www.dxlc.com/solar/ ] has produced [ http://pao.gsfc.nasa.gov/gsfc/spacesci/solarexp/soho.htm ] at least three strong flares and a large coronal mass ejection (CME) since Tuesday, June 6th [ http://sohowww.nascom.nasa.gov/hotshots/ ]. This recent [ http://umbra.nascom.nasa.gov/images/latest.html ] false color X-ray image [ http://www.lmsal.com/SXT/Oimages.html ] of the Sun shows the active region generating the explosive events, here the Sun's [ http://antwrp.gsfc.nasa.gov/apod/ap981221.html ] most intense source of X-rays [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ history_xray.html ], as the dominant bright area just above center. X-ray hot plasma suspended in looping magnetic fields arcs above this region, cataloged as AR9026. AR9026 appears as a large group of sunspots [ http://es.rice.edu/ES/humsoc/Galileo/Things/ sunspots.html ] in visible light images. The three intense flares were all X-class events, the most severe class of solar flares based on X-ray flux measurements [ http://sec.noaa.gov/rt_plots/xray_5m.cgi ] by the earth-orbiting GOES [ http://www.earth.nasa.gov/history/goes/goes.html ] satellites. Energetic particles from the CME [ http://antwrp.gsfc.nasa.gov/apod/ap000309.html ], associated with the second X-class flare, were directed toward [ http://www.spaceweather.com/images/new/cme.html ] planet Earth and could produce geomagnetic storms [ http://sec.noaa.gov/NOAAscales/index.html ] as early as today. Possible effects range from increased auroral displays [ http://sec.noaa.gov/pmap/index.html ] to disruptions of satellite and communications systems and electrical power grids. But wait ... there's more! In the coming days AR9026, carried slowly across the Sun (from left to right) by solar rotation [ http://antwrp.gsfc.nasa.gov/apod/ap991021.html ], is likely to produce even more solar flares [ http://hesperia.gsfc.nasa.gov/sftheory/ ]. |
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Sunspot Stack
| Title |
Sunspot Stack |
| Explanation |
Welcome to multiwavelength astronomy [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ multiwavelength.html ]! From top to bottom, these stacked panels show the largest sunspot group in a decade in visible, extreme ultraviolet, and x-ray light. All were taken on March 29, around the time [ http://sohowww.nascom.nasa.gov/hotshots/2001_03_29/ ] the famous solar active region, cataloged as AR 9393 [ http://antwrp.gsfc.nasa.gov/apod/ap010411.html ], was at its peak size -- over 10 times the size of planet Earth. The panels illustrate how the "appearance" of the active region changes, when imaged in electromagnetic radiation [ http://www.colorado.edu/physics/2000/ waves_particles/ ] (light) of progressively shorter wavelengths. In the visible light panel, dark islands [ http://antwrp.gsfc.nasa.gov/apod/ap010315.html ] of sunspots stand out against the bright solar surface, but the situation seems to be reversed in the extreme ultraviolet panel with a bright active region seen against a darker background. Finally, the x-ray panel reveals majestic loops of glowing plasma arcing far above the sunspot group. Why do pictures [ http://www.lmsal.com/YPOP/SOLARWEEK/ ] of the same part of the Sun [ http://observe.ivv.nasa.gov/nasa/exhibits/sun/sun_1.html ] look so different? Made at different wavelengths, each panel actually records a different layer [ http://www.lmsal.com/YPOP/Spotlight/SunInfo/ Structure.html ] in the solar atmosphere. Top to bottom, the altitude of each layer (along with temperature) increases, starting with the Sun's visible surface or photosphere [ http://solar-center.stanford.edu/hidden-pic/ photosphere.html ] (about 5 thousand kelvins), then the chromosphere [ http://science.nasa.gov/ssl/pad/solar/ chromos.htm ] / transition region [ http://science.nasa.gov/ssl/pad/solar/t_region.htm ] (ten to a hundred thousand kelvins [ http://lamar.colostate.edu/~hillger/temps.htm ]), and finally the solar corona [ http://www.lmsal.com/YPOP/Spotlight/Tour/ corona2.html ] (millions of kelvins). |
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Perihelion Sun
| Title |
Perihelion Sun |
| Explanation |
The Earth's orbit is not a perfect, sun-centered circle. At "aphelion", the most distant point in Earth's orbit [ http://www.lmsal.com/YPOP/Classroom/Lessons/Eccentricity/ ], the Sun is 150 million kilometers away and at "perihelion", the closest point, Earth approaches the Sun to within about 147 million kilometers. While aphelion occurs in July, perihelion for planet Earth comes in [ http://aa.usno.navy.mil/AA/data/docs/EarthSeasons.html ] January. In fact, inhabitants of the Northern Hemisphere, particularly those wearily weathering winter storms, may be surprised to learn that Earth reached its closest point [ http://www.earthsky.com/1996/es960103.html ] to the Sun on January 3rd this year. This false-color picture [ http://www.lmsal.com/SXT/html2/Last_SXT_Image.html ] recorded near perihelion is from the earth-orbiting Yohkoh Solar Observatory. It shows an increasingly active Sun [ http://www.solar.isas.ac.jp/sxt_co/990108.html ] in the light of X-rays [ http://antwrp.gsfc.nasa.gov/apod/ap981221.html ]. A negative color scheme is used, darker colors representing more intense X-ray light. |
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Sigmoids Predict Solar Erupt
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| Title |
Sigmoids Predict Solar Eruptions |
| Explanation |
On the Sun [ http://www.seds.org/nineplanets/nineplanets/sol.html ], S marks the spot. Solar explosions have been discovered [ http://science.nasa.gov/newhome/headlines/ast09mar99_1.htm ] to explode preferentially from regions marked with this letter. The surface of the quiet Sun [ http://antwrp.gsfc.nasa.gov/apod/ap970108.html ] is a maze of hot gas and flowing magnetic fields [ http://vestige.lmsal.com/TRACE/Public/magnetic.htm ]. When two regions of high magnetic field strength approach each other, they typically pass uneventfully. If the two regions pass close enough and in just the right way, however, an X-ray [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ] bright S-shaped region called a sigmoid [ ftp://ftp.hq.nasa.gov/pub/pao/pressrel/1999/99-035.txt ] forms and quickly explodes in a Coronal Mass Ejection [ http://www-istp.gsfc.nasa.gov/istp/outreach/cmeposter/hurricane.html ] (CME). Astronomers conjecture that in the center of the sigmoid, a circuit closes that somehow drives the explosion. The above picture [ http://solar.physics.montana.edu/canfield/sigmoids.shtml ] shows the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap980830.html ] in X-ray light. A pre-CME [ http://antwrp.gsfc.nasa.gov/apod/ap961108.html ] sigmoid is shown on the left inset image, while a post-CME [ http://www-solar.dcs.st-and.ac.uk/~alan/sun_course/Introduction/Coronal_mass_ejection.html ] arc is shown in the right inset. |
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X-Ray Triple Jet
| Title |
X-Ray Triple Jet |
| Explanation |
Recorded on July 7, 1998 [ http://www.solar.isas.ac.jp/sxt_co/980711.html ], this animation using X-ray [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ] images [ http://imagine.gsfc.nasa.gov/docs/science/how_l1/images.html ] of the Sun shows an amazing event - three nearly simultaneous jets connected with solar active regions. The two frames were taken several hours apart by the Soft X-ray Telescope on board the orbiting Yohkoh observatory [ http://www.solar.isas.ac.jp/english/index.html ]. They have a "negative" color scheme, the darker colors representing more intense X-rays from the corona [ http://antwrp.gsfc.nasa.gov/apod/ap990716.html ] and active regions [ http://antwrp.gsfc.nasa.gov/apod/ap980616.html ] on the solar surface. The pictures clearly show two curving jets of X-ray hot plasma appearing above the solar equator and one below. A sharp vertical stripe near the jet above center is a digital blemish while the overall shift of the image is due to solar rotation. As the Sun [ http://www.lmsal.com/SXT/html2/list.html ] is now approaching the active part of its 11 year cycle [ http://www.sunspotcycle.com/ ], numerous single jets have been seen. But the appearance of these three widely separated jets at once is considered an unlikely coincidence and has fueled current speculations about their origins. |
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