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The main noteworthy feature
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| Description |
The main noteworthy feature on the Sun this past week is the one, dark, coronal hole that we watched as it rotated to the Sun's center over three days (June 17-19, 2007). Anyone who inspects the movie carefully will note that there were no looping arcs, no flares or solar storms, no filaments, and no bright active regions. Yes, the Sun remained largely featureless except for the coronal hole, and even that hole is not particularly large as these things go. We should note too that the north and the south poles of the Sun also have polar coronal holes that are becoming more distinct as we approach solar minimum. Coronal holes are cooler, darker areas when observed in extreme ultraviolet light as the Sun is here. Since coronal holes are 'open' magnetically, strong solar wind gusts can escape from them and carry solar particles out to our magnetosphere and beyond. The Sun is near its minimum period of activity in its 11-year solar cycle and it shows it in this way. |
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Dark Sun Sizzling
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Dark Sun Sizzling |
| Explanation |
Is this our Sun? Yes. Even on a normal day, our Sun is sizzling [ http://antwrp.gsfc.nasa.gov/apod/ap970106.html ] ball [ http://antwrp.gsfc.nasa.gov/apod/ap970107.html ] of seething [ http://antwrp.gsfc.nasa.gov/apod/ap970108.html ] hot gas [ http://antwrp.gsfc.nasa.gov/apod/ap030729.html ]. Unpredictably, regions of strong and tangled magnetic fields [ http://www-spof.gsfc.nasa.gov/Education/whmfield.html ] arise, causing sunspots [ http://antwrp.gsfc.nasa.gov/apod/ap051106.html ] and bright active regions [ http://antwrp.gsfc.nasa.gov/apod/ap040726.html ]. The Sun's surface bubbles [ http://en.wikipedia.org/wiki/Granule_%28solar_physics%29 ] as hot hydrogen [ http://en.wikipedia.org/wiki/Hydrogen ] gas streams along looping magnetic fields. These active regions channel gas along magnetic loops [ http://antwrp.gsfc.nasa.gov/apod/ap050814.html ], usually falling back but sometimes escaping into the solar corona [ http://antwrp.gsfc.nasa.gov/apod/ap010408.html ] or out into space as the solar wind [ http://science.nasa.gov/ssl/pad/solar/sun_wind.htm ]. Pictured above is our Sun in three colors of ultraviolet [ http://imagers.gsfc.nasa.gov/ems/uv.html ] light. Since only active regions emit significant amounts of energetic ultraviolet light, most of the Sun appears dark. The colorful portions glow spectacularly, pinpointing the Sun's hottest and most violent regions [ http://antwrp.gsfc.nasa.gov/apod/ap060502.html ]. Although the Sun is constantly changing, the rate of visible [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/emspectrum.html ] light it emits has been relatively stable [ http://en.wikipedia.org/wiki/Solar_constant ] over the past five billion years, allowing life to emerge [ http://www.pbs.org/wgbh/nova/origins/life-nf.html ] on Earth. |
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Diamond Ring in the Sun
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Diamond Ring in the Sun |
| Explanation |
Today, earthbound skygazers can celebrate a solstice [ http://www-spof.gsfc.nasa.gov/stargaze/Sseason.htm ], a new Moon [ http://aa.usno.navy.mil/faq/docs/moon_phases.html ], the closest approach [ http://mars.jpl.nasa.gov/ ] of planet Mars since 1988 ... oh yes, and a total eclipse of the Sun, the first total solar eclipse [ http://sunearth.gsfc.nasa.gov/eclipse/TSE2001/TSE2001.html ] of the third millennium. Of course for some, today's most spectacular celestial views will be of the eclipsed Sun [ http://science.nasa.gov/headlines/y2001/ast19jun_1.htm ] from along the path of totality as the new Moon's shadow tracks across southern Africa and Madagascar [ http://www.madagascar-eclipse2001.com/eclipse_.htm ]. This picture from the August 1999 total solar eclipse captures the shimmering solar corona just as that eclipse's total phase ended, as seen from eastern Turkey. The first rays of bright sunlight shinning through edge-on [ http://sunearth.gsfc.nasa.gov/eclipse/TSE2001/TSE2001fig/ TSE2001fig08.GIF ] lunar mountains and valleys create the fleeting appearance of glistening diamonds set in a ring around the Moon's silhouette. Do you want to see today's solar eclipse? Eclipse expeditions are offering live webcasts [ http://www.bit-net.com/~pauer/eclipse01/ ]. |
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S is for Sun
| Title |
S is for Sun |
| Explanation |
Taken yesterday from the SOHO spacecraft, this false-color image shows [ http://sohowww.nascom.nasa.gov/explore/ Sun_Obs.html ] the active Sun near [ http://www.athropolis.com/sunrise/def-sol2.htm ] the March Equinox [ http://www2.worldbook.com/features/features.asp? feature=seasons&page=html/seasons.htm&direct=yes ], the beginning of Autumn in the south and Spring in the northern hemisphere. Recorded [ http://sohowww.nascom.nasa.gov/data/ latestimages.html# ] in a band of extreme ultraviolet light emitted by highly ionized iron [ http://antwrp.gsfc.nasa.gov/apod/ap010929.html ] atoms, the Sun's upper atmosphere or solar corona [ http://science.msfc.nasa.gov/ssl/pad/solar/ corona.htm ] shines with an array of active regions and plasma loops suspended in magnetic [ http://science.msfc.nasa.gov/ssl/pad/solar/ the_key.htm ] fields. The bright coronal structures and loops seen here have temperatures of about 1.5 million kelvins [ http://antoine.fsu.umd.edu/chem/senese/101/measurement/faq/ why-273.15-kelvin.shtml ]. By chance, the Sun's earth-facing [ http://antwrp.gsfc.nasa.gov/apod/ap010503.html ] side also seems to be marked with a twisting complex of dark filament channels [ http://sohowww.nascom.nasa.gov/explore/ filament.html ] shaped like a giant "S". Filaments represent relatively (!) cool material in the corona which show up as prominences when seen at the Sun's edge. For planet Earth, recent [ http://spaceweather.com/ ] solar activity has made auroral displays likely around this year's March Equinox [ http://antwrp.gsfc.nasa.gov/apod/ap010330.html ]. |
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A Planet Transits the Sun
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A Planet Transits the Sun |
| Explanation |
Today an astronomical event will occur that no living person has ever seen: Venus will cross [ http://sunearth.gsfc.nasa.gov/sunearthday/2004/vt_edu2004_venus_back_his.htm ] directly in front of the Sun. A Venus crossing [ http://sunearth.gsfc.nasa.gov/sunearthday/2004/index_vthome.htm ], called a transit, last occurred in 1882 and was front-page [ http://image.gsfc.nasa.gov/poetry/venus/News/NYT12071882.pdf ] news [ http://image.gsfc.nasa.gov/poetry/venus/News/News.html ] around the world. Today's transit will be visible [ http://skyandtelescope.com/observing/objects/planets/article_1021_1.asp ] in its entirety throughout Europe and most of Asia and Africa. The northeastern half of North America [ http://science.nasa.gov/headlines/y2004/02jun_viewersguide.htm ] will see the Sun rise with the dark dot of Venus [ http://www.saao.ac.za/~wpk/tov1882/tovwell.html ] already superposed. Never look directly at the Sun [ http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/safety.html ], even when Venus is in front [ http://image.gsfc.nasa.gov/poetry/venus/TransitFAQs.html ]. Mercury's closer proximity to the Sun cause it to transit every few years. In fact, the above image mosaic of Mercury crossing the Sun [ http://www.space.com/scienceastronomy/venus_transit_2004.html ] is from two [ http://antwrp.gsfc.nasa.gov/apod/ap991119.html ] transits [ http://antwrp.gsfc.nasa.gov/apod/ap991210.html ] ago [ http://antwrp.gsfc.nasa.gov/apod/ap030513.html ], in November 1999. Will anyone living see the next Venus transit [ http://www.astronomy.com/content/dynamic/articles/000/000/001/745fvezh.asp ]? Surely yes since it occurs in 2012. |
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A Seemingly Square Sun
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A Seemingly Square Sun |
| Explanation |
Isn't the Sun [ http://www.seds.org/nineplanets/nineplanets/sol.html ] round? Yes, but in the above picture, the Earth's atmosphere [ http://www.aspire.cs.uah.edu/~jonesj/r.html ] makes it appear almost square. Here a layer of air near the Earth was so warm it acted like a giant lens [ http://www.atm.damtp.cam.ac.uk/people/mgb/refraction.html ], creating increasingly distorted paths for sunlight to reach the camera. Similarly, on a long flat highway, it may appear that the road in the distance is covered with water. In this case, light from the blue sky [ http://math.ucr.edu/home/baez/physics/blue_sky.html ] is being unusually refracted [ http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/opt/mch/refr/less.rxml ] by warm air just above the dry road. No matter how the Earth's atmosphere [ http://csep10.phys.utk.edu/astr161/lect/earth/atmosphere.html ] makes the Sun appear, the Sun [ http://www.hawastsoc.org/solar/eng/sun.htm ] will always be spherical. This setting Sun was photographed [ http://www.psiaz.com/polakis/dayatmos/dayatmos.html ] over Lake Michigan [ http://www.epa.gov/grtlakes/lakemich/lampf.html ] in Muskegon [ http://www.ci.muskegon.mi.us/ ], MI. |
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Syrtis Major
PIA03786
Sol (our sun)
Thermal Emission Imaging Sys
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| Title |
Syrtis Major |
| Original Caption Released with Image |
(Released 1 May 2002) The Science This image is from the region of Syrtis Major, which is dominated by a low-relief shield volcano. This area is believed to be an area of vigorous aeolian activity with strong winds in the east-west direction. The effects of these winds are observed as relatively bright streaks across the image, extending from topographic features such as craters. The brighter surface material probably indicates a smaller relative particle size in these areas, as finer particles have a higher albedo. The bright streaks seen off of craters are believed to have formed during dust storms. A raised crater rim can cause a reduction in the wind velocity directly behind it, which results in finer particles being preferentially deposited in this location. In the top half of the image, there is a large bright streak that crosses the entire image. There is no obvious topographic obstacle, therefore it is unclear whether it was formed in the same manner as described above. This image is located northwest of Nili Patera, a large caldera in Syrtis Major. Different flows from the caldera eruptions can be recognized as raised ridges, representing the edge of a flow lobe. The Story In the 17th century, Holland was in its Golden Age, a time of cultural greatness and immense political and economic influence in the world. In that time, lived a inquisitive person named Christian Huygens. As a boy, he loved to draw and to figure out problems in mathematics. As a man, he used these talents to make the first detailed drawings of the Martian surface - - only 50 years or so after Galileo first turned his telescope on Mars. Mars suddenly became something other than a small red dot in the sky. One of the drawings Huygens made was of a dark marking on the red planet's surface named Syrtis Major. Almost 350 years later, here we are with an orbiter that can show us this place in detail. Exploration lives! It's great we can study this area up close. In earlier periods of history, scientists were fascinated with Syrtis Major because this dark region varied so much through the seasons and years. Some people thought it might be a changing sea, and others thought it might be vegetation. Early spacecraft like Mariner and Viking revealed for the first time that the changes were caused by the wind blowing dust and sand across the surface. What we can see in this image is exactly that: evidence of a lot of wind action. Bright dust patches streak across this image, formed through wind interference from craters and other landforms. These wispy, bright streaks are spread on the surface by a vigorous, east-west wind that kicked up huge dust storms, scattering the fine particles of sand and dust in an almost etherial pattern. The bright streaks in the top part of the image might have formed in a slightly different way, because there is no landform standing in the wind's way. Beneath the bright surface dust are raised ridges that mark the edges of earlier lava flows, from Nili Patera, a Martian "caldera." A caldera is a collapsed, bowl-shaped depression at the top of a volcano cone. Can you imagine how Christian Huygens would feel if he lived today and could see all of this knowledge unfold? Or how it would feel to be the first person to stand in this dark volcanic and cratered region, knowing how many discovers had paved the way to that moment? Yes, exploration lives! |
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Syrtis Major
PIA03786
Sol (our sun)
Thermal Emission Imaging Sys
…
| Title |
Syrtis Major |
| Original Caption Released with Image |
(Released 1 May 2002) The Science This image is from the region of Syrtis Major, which is dominated by a low-relief shield volcano. This area is believed to be an area of vigorous aeolian activity with strong winds in the east-west direction. The effects of these winds are observed as relatively bright streaks across the image, extending from topographic features such as craters. The brighter surface material probably indicates a smaller relative particle size in these areas, as finer particles have a higher albedo. The bright streaks seen off of craters are believed to have formed during dust storms. A raised crater rim can cause a reduction in the wind velocity directly behind it, which results in finer particles being preferentially deposited in this location. In the top half of the image, there is a large bright streak that crosses the entire image. There is no obvious topographic obstacle, therefore it is unclear whether it was formed in the same manner as described above. This image is located northwest of Nili Patera, a large caldera in Syrtis Major. Different flows from the caldera eruptions can be recognized as raised ridges, representing the edge of a flow lobe. The Story In the 17th century, Holland was in its Golden Age, a time of cultural greatness and immense political and economic influence in the world. In that time, lived a inquisitive person named Christian Huygens. As a boy, he loved to draw and to figure out problems in mathematics. As a man, he used these talents to make the first detailed drawings of the Martian surface - - only 50 years or so after Galileo first turned his telescope on Mars. Mars suddenly became something other than a small red dot in the sky. One of the drawings Huygens made was of a dark marking on the red planet's surface named Syrtis Major. Almost 350 years later, here we are with an orbiter that can show us this place in detail. Exploration lives! It's great we can study this area up close. In earlier periods of history, scientists were fascinated with Syrtis Major because this dark region varied so much through the seasons and years. Some people thought it might be a changing sea, and others thought it might be vegetation. Early spacecraft like Mariner and Viking revealed for the first time that the changes were caused by the wind blowing dust and sand across the surface. What we can see in this image is exactly that: evidence of a lot of wind action. Bright dust patches streak across this image, formed through wind interference from craters and other landforms. These wispy, bright streaks are spread on the surface by a vigorous, east-west wind that kicked up huge dust storms, scattering the fine particles of sand and dust in an almost etherial pattern. The bright streaks in the top part of the image might have formed in a slightly different way, because there is no landform standing in the wind's way. Beneath the bright surface dust are raised ridges that mark the edges of earlier lava flows, from Nili Patera, a Martian "caldera." A caldera is a collapsed, bowl-shaped depression at the top of a volcano cone. Can you imagine how Christian Huygens would feel if he lived today and could see all of this knowledge unfold? Or how it would feel to be the first person to stand in this dark volcanic and cratered region, knowing how many discovers had paved the way to that moment? Yes, exploration lives! |
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