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Mysterious Blob Galaxies Rev …
Title Mysterious Blob Galaxies Revealed
Description This image composite shows a giant galactic blob (red, left) and the three merging galaxies NASA's Spitzer Space Telescope discovered within it (yellow, right). Blobs are intensely glowing clouds of hot hydrogen gas that envelop faraway galaxies. They are about 10 times as large as the galaxies they surround. Visible-light images like the one shown here (left), reveal the vast extent of blobs, but don't provide much information about their host galaxies. Using its heat-seeking infrared eyes, Spitzer was able to see the dusty galaxies tucked inside one well-known blob located 11 billion light-years away. The findings reveal three monstrously bright galaxies, trillions of times brighter than the Sun, in the process of merging together (right). Spitzer also observed three other blobs located in the same cosmic neighborhood, all of which were found to be glaringly bright. One of these blobs is also known to be a galactic merger, only between two galaxies instead of three. It remains to be seen whether the final two blobs studied also contain mergers. The Spitzer data were acquired by its multiband imaging photometer. The visible-light image was taken by the Blanco Telescope at the Cerro Tololo Inter-American Observatory, Chile.
Mysterious Blob Galaxies Rev …
Title Mysterious Blob Galaxies Revealed
Description This image composite shows a giant galactic blob (red, left) and the three merging galaxies NASA's Spitzer Space Telescope discovered within it (yellow, right). Blobs are intensely glowing clouds of hot hydrogen gas that envelop faraway galaxies. They are about 10 times as large as the galaxies they surround. Visible-light images like the one shown here (left), reveal the vast extent of blobs, but don't provide much information about their host galaxies. Using its heat-seeking infrared eyes, Spitzer was able to see the dusty galaxies tucked inside one well-known blob located 11 billion light-years away. The findings reveal three monstrously bright galaxies, trillions of times brighter than the Sun, in the process of merging together (right). Spitzer also observed three other blobs located in the same cosmic neighborhood, all of which were found to be glaringly bright. One of these blobs is also known to be a galactic merger, only between two galaxies instead of three. It remains to be seen whether the final two blobs studied also contain mergers. The Spitzer data were acquired by its multiband imaging photometer. The visible-light image was taken by the Blanco Telescope at the Cerro Tololo Inter-American Observatory, Chile.
Mysterious Blob Galaxies Rev …
Title Mysterious Blob Galaxies Revealed
Description This image composite shows a giant galactic blob (red, left) and the three merging galaxies NASA's Spitzer Space Telescope discovered within it (yellow, right). Blobs are intensely glowing clouds of hot hydrogen gas that envelop faraway galaxies. They are about 10 times as large as the galaxies they surround. Visible-light images like the one shown here (left), reveal the vast extent of blobs, but don't provide much information about their host galaxies. Using its heat-seeking infrared eyes, Spitzer was able to see the dusty galaxies tucked inside one well-known blob located 11 billion light-years away. The findings reveal three monstrously bright galaxies, trillions of times brighter than the Sun, in the process of merging together (right). Spitzer also observed three other blobs located in the same cosmic neighborhood, all of which were found to be glaringly bright. One of these blobs is also known to be a galactic merger, only between two galaxies instead of three. It remains to be seen whether the final two blobs studied also contain mergers. The Spitzer data were acquired by its multiband imaging photometer. The visible-light image was taken by the Blanco Telescope at the Cerro Tololo Inter-American Observatory, Chile.
Brief History of the Univers …
Title Brief History of the Universe
Description This artist's timeline chronicles the history of the universe, from its explosive beginning to its mature, present-day state. Our universe began in a tremendous explosion known as the Big Bang about 13.7 billion years ago (left side of strip). Observations by NASA's Cosmic Background Explorer and Wilkinson Anisotropy Microwave Probe revealed microwave light from this very early epoch, about 400,000 years after the Big Bang, providing strong evidence that our universe did blast into existence. Results from the Cosmic Background Explorer were honored with the 2006 Nobel Prize for Physics. A period of darkness ensued, until about a few hundred million years later, when the first objects flooded the universe with light. This first light is believed to have been captured in data from NASA's Spitzer Space Telescope. The light detected by Spitzer would have originated as visible and ultraviolet light, then stretched, or redshifted, to lower-energy infrared wavelengths during its long voyage to reach us across expanding space. The light detected by the Cosmic Background Explorer and the Wilkinson Anisotropy Microwave Probe from our very young universe traveled farther to reach us, and stretched to even lower-energy microwave wavelengths. Astronomers do not know if the very first objects were either stars or quasars. The first stars, called Population III stars (our star is a Population I star), were much bigger and brighter than any in our nearby universe, with masses about 1,000 times that of our sun. These stars first grouped together into mini-galaxies. By about a few billion years after the Big Bang, the mini-galaxies had merged to form mature galaxies, including spiral galaxies like our own Milky Way. The first quasars ultimately became the centers of powerful galaxies that are more common in the distant universe. NASA's Hubble Space Telescope has captured stunning pictures of earlier galaxies, as far back as ten billion light-years away.
Iapetus Thermal Radiation Im …
Description Iapetus Thermal Radiation Image
Full Description This image of the infrared heat radiation from Saturn's moon Iapetus was obtained by the Cassini composite infrared spectrometer instrument 16 hours before Cassini's closest approach to this mysterious moon, on December 31, 2004. The thermal radiation is shown as both a grayscale image, equivalent to what we would see if our eyes were sensitive to infrared wavelengths near 15 microns, and as a color-coded temperature map. A previously-released mosaic obtained by Cassini's imaging camera shortly before the composite infrared spectrometer observation, with similar scale and orientation, is also shown for comparison. Temperatures reach nearly 130 Kelvin (-226 Fahrenheit) at noon on the equator on the dark material that covers most of this side of Iapetus, making high noon on Iapetus's dark side probably the warmest places in the Saturn system. This is much warmer than temperatures on another Saturnian moon, Phoebe, measured by composite infrared spectrometer in June 2004. Those Phoebe temperature measurements peaked near 112 Kelvin (-258 Fahrenheit), because though Phoebe is almost as dark as Iapetus's dark material and absorbs nearly as much sunlight, Phoebe rotates much more quickly (once every 9 hours, compared to 79 days for Iapetus). That means the surface has less time to heat up during the day. Temperatures on Iapetus's bright material are much colder, peaking near 100 Kelvin (-280 Fahrenheit), both because the bright material absorbs less sunlight and because it is further from the equator on this side of Iapetus. Temperatures in the large crater near the center of the disc are slightly different from those in surrounding areas, because sloping surfaces within the crater are warmer where they are tilted towards the Sun and cooler when tilted away from the Sun. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission visit, http://saturn.jpl.nasa.gov and the instrument team's home page, http://cirs.gsfc.nasa.gov/. *Credit*: NASA/JPL/GSFC
Date January 10, 2005
Iapetus Temperature Variatio …
Description Iapetus Temperature Variation Map
Full Description This plot shows how daytime temperatures at low latitudes on the dark material on Saturn's moon Iapetus vary with time of day, from about 130 Kelvin (-226 Fahrenheit) at noon to about 70 Kelvin (-334 Fahrenheit) at sunset. The observations are compared to a "forecast" model (green line) which predicts temperatures based on an assumed value of a parameter called the "thermal inertia. This measures how well the surface can retain heat as conditions change. Rock or solid ice has a high thermal inertia, roughly 2,000,000 as measured in the obscure units used for thermal inertia, meaning that it is good at storing heat and cools down or heats up relatively slowly. On Iapetus, in contrast, temperatures drop precipitously in the afternoon as the Sun sinks towards the horizon, and a very small value of the thermal inertia (30,000 units) is needed in the model to match the data. This means that Iapetus's surface is extremely bad at storing heat, and is thus extremely fluffy, probably due to the pulverizing effect of billions of years of meteorite impacts, though the mysterious process that has darkened this side of Iapetus may also have played a role. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission visit, http://saturn.jpl.nasa.gov and the instrument team's home page, http://cirs.gsfc.nasa.gov/. *Credit*: NASA/JPL/GSFC
Date January 10, 2005
Enceladus Temperature Map
Description Enceladus Temperature Map
Full Description This image shows the surprise that startled Cassini scientists on the composite infrared spectrometer team when they got their first look at the infrared (heat) radiation from the south pole of Saturn's moon Enceladus. There is a dramatic warm spot centered on the pole that is probably a sign of internal heat leaking out of the icy moon. The data were taken during the spacecraft's third flyby of this intriguing moon on July 14, 2005. Based on data from previous flybys, which did not show the south pole well, team members expected that the south pole would be very cold, as shown in the left panel. Enceladus is one of the coldest places in the Saturn system because its extremely bright surface reflects 80 percent of the sunlight that hits it, so only 20 percent is available to heat the surface. As on Earth, the poles should be even colder than the equator because the sun shines at such an oblique angle there. The right hand panel shows a global temperature image made from measurements of Enceladus' heat radiation at wavelengths between 9 and 16.5 microns. Cassini made the observation from a distance of 84,000 kilometers (52,000 miles) on the approach to Enceladus, and the image shows details as small as 25 kilometers (16 miles). Equatorial temperatures are much as expected, topping out at about 80 degrees Kelvin (-315 degrees Fahrenheit), but the south pole is occupied by a well-defined warm region reaching 85 Kelvin (-305 degrees Fahrenheit). That is 15 degrees Kelvin (27 degrees Fahrenheit) warmer than expected. The composite infrared spectrometer data further suggest that small areas of the pole are at even higher temperatures, well over 110 degrees Kelvin (-261 degrees Fahrenheit). Evaporation of this relatively warm ice probably generates the cloud of water vapor detected above Enceladus' south pole by several other Cassini instruments. The south polar temperatures are very difficult to explain if sunlight is the only energy source heating the surface, though exotic sunlight-trapping mechanisms have not yet been completely ruled out. It therefore seems likely that portions of the polar region are warmed by heat escaping from the interior of the moon. This would make Enceladus only the third solid body in the solar system, after Earth and Jupiter's volcanic moon Io, where hot spots powered by internal heat have been detected. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The composite infrared spectrometer team homepage is, http://cirs.gsfc.nasa.gov/ . Credit: NASA/JPL/GSFC
Date July 29, 2005
Phoebe Temperature Maps
Description Phoebe Temperature Maps
Full Description A montage of maps of Saturn's moon Phoebe shows surface temperatures at various times of day as determined by the composite infrared spectrometer onboard Cassini during the June 11, 2004, Phoebe flyby. The asterisk on each map shows the location of the subsolar point, where the Sun is directly overhead. This point moves across the surface as Phoebe rotates. It is morning in regions to the left of the subsolar point, and afternoon in regions to the right. Like a newspaper weather map, different colors indicate different temperatures, though Phoebe's temperatures are distinctly cooler than even the coldest January day on Earth. Equatorial temperatures peak in the early afternoon near 112 Kelvin (-257 Fahrenheit), plunging to 78 Kelvin (-319 Fahrenheit) before dawn, and are even colder at higher latitudes. The large day/night temperature contrasts imply that Phoebe's surface is covered in loose dust or ice particles that store little heat and thus cool off rapidly at night. Regions of Phoebe's surface that were not observed are shown in black. Most of the maps show the effect on surface temperatures of the large crater-like depression seen in Cassini's visible-wavelength images of Phoebe, which is located just left of center in these maps. Crater walls that are shadowed and cold in the early morning in the first map are sunlit and warm in the late afternoon in the final map. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini composite infrared spectrometer home page at http://cirs.gsfc.nasa.gov/ . Image Credit: NASA/JPL/Goddard Space Flight Center
Slower Spinning Rings #1
Description Slower Spinning Rings #1
Full Description The Cassini composite infrared spectrometer obtained temperature maps of Saturn's main rings (A, B and C) that showed ring temperatures decreasing with increasing solar phase angle (the change of the sun-spacecraft-ring angle) on both the lit and unlit sides of the rings. Temperature changes throughout Saturn's main rings, as measured by the instrument, indicate that Saturn ring particles spin slowly compared to their orbital periods of 6 to 14 hours. They may spin several times per orbit to less than one time per orbit. Scans are shown for the lit and unlit rings, at relatively low (less than 60-degree) and high (more than 130-degree) phase angles. Each scan was painted on the rings at the correct ring orientation, creating a false color image. Warmer temperatures about minus 262 degrees Fahrenheit (110 Kelvin) are shown in red and cooler temperatures about minus 343 degrees (65 K) are shown in blue. Other colors indicate temperatures between minus 343 degrees and minus 262 degrees (65 K and 110 K). The scans of the lit rings are shown in the two panels on the left and scans of the unlit rings are shown in the two panels on the right. The thermal characteristics of each main ring vary noticeably with phase angle. Radial scans of the A, B and C rings show a decrease in temperature with increasing phase angle for both the lit and unlit sides of the rings. The C ring and Cassini Division exhibit the largest change in temperature. The temperature of the lit C ring decreases by about 22 degrees (12 Kelvin) between low and high phase angles. A similar contrast is present for the unlit side of the C ring. The C ring and Cassini Division are darker than the A and B rings so they can absorb more heat from the Sun. The lit B ring shows a temperature contrast of approximately 18 degrees (10 K) while the unlit B ring shows very little thermal contrast. Very little sunlight may make it through the thick B ring to its unlit side. The lit A ring is particularly interesting because the magnitude of the thermal contrast decreases with increasing radial distance from Saturn. The outer A ring shows only a small temperature change with phase angle, possibly because it contains smaller, or more rapidly rotating ring particles, which would have more uniform temperatures with phase angle. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission visit, http://saturn.jpl.nasa.gov and the instrument team's home page, http://cirs.gsfc.nasa.gov/. Credit: NASA/JPL/GSFC
Date September 5, 2005
Slower Spinning Rings #2
Description Slower Spinning Rings #2
Full Description Temperature changes mapped with Cassini's composite and infrared spectrometer throughout Saturn's main rings show the ring temperatures decreasing with the increase of the Sun-spacecraft-ring angle (called phase angle) on both the lit and unlit sides of the rings. These temperature changes indicate that the ring particles spin slowly compared to their orbital periods of 6 to 14 hours. They may spin several times per orbit to less than one time per orbit. Four scans are shown for the lit and unlit rings, at relatively low (less than 60 degrees) and high (more than 130 degrees) phase angles. Warmer temperatures about minus 262 degrees Fahrenheit (110 Kelvin) are shown in red and cooler temperatures about minus 343 degrees (65 K) are shown in blue. Other colors indicate temperatures between minus 343 degrees and minus 262 degrees (65 K and 110 K). The top two scans are for the lit rings and the bottom two scans are for the unlit rings. The change in ring temperature between each scan can be seen clearly. The thermal characteristics of each main ring vary noticeably with phase angle. Radial scans of the A, B and C rings show a decrease in temperature with increasing phase angle for both the lit and unlit sides of the rings. The C ring and Cassini Division exhibit the largest change in temperature. The temperature of the lit C ring decreases by about 22 degrees (12 Kelvin) between low and high phase angles. A similar contrast is present for the unlit side of the C ring. The C ring and Cassini Division are darker than the A and B rings so they can absorb more heat from the Sun. The lit B ring shows a temperature contrast of approximately 18 degrees (10 K) while the unlit B ring shows very little thermal contrast. Very little sunlight may make it through the thick B ring to its unlit side. The lit A ring is particularly interesting because the magnitude of the thermal contrast decreases with increasing radial distance from Saturn. The outer A ring shows only a small temperature change with phase angle, possibly because it contains smaller, or more rapidly rotating ring particles, which would have more uniform temperatures with phase angle. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission visit, http://saturn.jpl.nasa.gov and the instrument team's home page, http://cirs.gsfc.nasa.gov/.
Date September 5, 2005
Iapetus Temperature Map
Description Iapetus Temperature Map
Full Description This temperature map of Saturn's moon Iapetus is constructed from observations of Iapetus's infrared heat radiation taken with the Cassini composite infrared spectrometer instrument during the Dec. 31, 2004 flyby. The orange asterisk marks the point on Iapetus where the Sun is directly overhead. Temperatures reach nearly 130 Kelvin (-226 Fahrenheit) at noon on the equator on the dark material that covers most of this side of Iapetus, making high noon on Iapetus's dark side probably the warmest places in the Saturn system. This is much warmer than temperatures on the moon Phoebe measured by the composite infrared spectrometer in June 2004, which peaked near 112 Kelvin (-258 Fahrenheit). That's because, although Phoebe is almost as dark as Iapetus's dark material and absorbs nearly as much sunlight, Phoebe rotates much more quickly (once every 9 hours, compared to 79 days for Iapetus). That means the surface has less time to heat up during the day. Temperatures on Iapetus' bright material are much colder, peaking near 100 Kelvin (-280 Fahrenheit), both because the bright material absorbs less sunlight and because it is further from the equator on this side of Iapetus. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission visit, http://saturn.jpl.nasa.gov and the instrument team's home page, http://cirs.gsfc.nasa.gov/. *Credit*: NASA/JPL/GSFC
Date January 10, 2005
Hubble Telescope Reveals Swa …
Title Hubble Telescope Reveals Swarm of Glittering Stars in Nearby Galaxy
General Information What is Hubble Heritage? A monthly showcase of new and archival Hubble images. Go to the Heritage site. Back to top [ #top ]
NASA Space Observatories Gli …
Title NASA Space Observatories Glimpse Faint Afterglow of Nearby Stellar Explosion
General Information What is Hubble Heritage? A monthly showcase of new and archival Hubble images. Go to the Heritage site. Back to top [ #top ]
Dying Star Sculpts Rungs of …
Title Dying Star Sculpts Rungs of Gas and Dust
Hubble Snaps Baby Pictures o …
Title Hubble Snaps Baby Pictures of Jupiter's "Red Spot Jr.
Hubble Observations Confirm …
Title Hubble Observations Confirm that Planets Form from Disks Around Stars
Spitzer and Hubble Capture E …
Title Spitzer and Hubble Capture Evolving Planetary Systems
Spitzer and Hubble Capture E …
Title Spitzer and Hubble Capture Evolving Planetary Systems
Spitzer and Hubble Capture E …
Title Spitzer and Hubble Capture Evolving Planetary Systems
Spitzer and Hubble Capture E …
Title Spitzer and Hubble Capture Evolving Planetary Systems
Spitzer and Hubble Capture E …
Title Spitzer and Hubble Capture Evolving Planetary Systems
The Carina Nebula: Star Birt …
Title The Carina Nebula: Star Birth in the Extreme
General Information What is Hubble Heritage? A monthly showcase of new and archival Hubble images. Go to the Heritage site. In celebration of the 17th anniversary of the launch and deployment of NASA's Hubble Space Telescope, a team of astronomers is releasing one of the largest panoramic images ever taken with Hubble's cameras. READ: Junior version of this article Amazing Space Learn about this story in the Star Witness, a science newspaper available on our sister site, Amazing Space. [ http://amazing-space.stsci.edu/news/archive/2007/02/ ] It is a 50-light-year-wide view of the central region of the Carina Nebula where a maelstrom of star birth &#151, and death &#151, is taking place. This image is a mosaic of the Carina Nebula assembled from 48 frames taken with Hubble's Advanced Camera for Surveys. The Hubble images were taken in the light of neutral hydrogen during March and July 2005. Color information was added with data taken in December 2001 and March 2003 at the Cerro Tololo Inter-American Observatory in Chile. Red corresponds to sulfur, green to hydrogen, and blue to oxygen emission.
Hubble Catches Jupiter Chang …
Title Hubble Catches Jupiter Changing Its Stripes
Elusive Planet Reshapes a Ri …
Title Elusive Planet Reshapes a Ring Around Neighboring Star
Hubble Finds Mysterious Disk …
Title Hubble Finds Mysterious Disk of Blue Stars Around Black Hole
Dusty Planetary Disks Around …
Title Dusty Planetary Disks Around Two Nearby Stars Resemble Our Kuiper Belt
General Information What is a News Nugget? News Nuggets are bulletins from the world of astronomy. These two bright debris disks of ice and dust appear to be the equivalent of our own solar system's Kuiper Belt, a ring of icy rocks outside the orbit of Neptune and the source of short-period comets. The disks encircle the types of stars around which there could be habitable zones and planets for life to develop. The disks seem to have a central area cleared of debris, perhaps by planets.
Brown Sun Bubbling
Title Brown Sun Bubbling
Explanation Our Sun may look like all soft and fluffy, but its not. Our Sun [ http://www.seds.org/nineplanets/nineplanets/sol.html ] is an extremely large ball of bubbling hot gas [ http://antwrp.gsfc.nasa.gov/apod/ap970108.html ], mostly hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ] gas. The above picture [ http://www.geocities.com/CapeCanaveral/Hall/6432/SUN.html ] was taken in a specific color of light emitted by hydrogen gas called Hydrogen-alpha [ http://www.nasm.edu/nasm/dsh/artifacts/SS-AlphaScope2.htm ]. Granules [ http://solar-center.stanford.edu/cgi-bin/quiz2.pl/granule_quiz.html ] cover the solar photosphere [ http://wwwssl.msfc.nasa.gov/ssl/pad/solar/surface.htm ] surface like shag carpet [ http://antwrp.gsfc.nasa.gov/apod/ap991024.html ], interrupted by bright regions containing dark sunspots [ http://antwrp.gsfc.nasa.gov/apod/ap981005.html ]. Visible at the left edge is a solar prominence [ http://antwrp.gsfc.nasa.gov/apod/ap970127.html ]. Our Sun glows because it is hot, but it is not on fire. Fire [ http://www.ci.phoenix.az.us/FIRE/homefire.html ] is the rapid acquisition of oxygen, and there is very little oxygen [ http://www.webelements.com/webelements/elements/text/key/O.html ] on the Sun. The energy source of our Sun is the nuclear fusion [ http://ippex.pppl.gov/ippex/About_fusion/fusion_doc2.html ] of hydrogen into helium [ http://www.webelements.com/webelements/elements/text/key/He.html ] deep within its core. Astronomers are still working to understand, however, why so few neutrinos [ http://antwrp.gsfc.nasa.gov/apod/ap980605.html ] are measured [ http://antwrp.gsfc.nasa.gov/apod/ap971028.html ] from the Sun's core.
Doomed Star Eta Carinae
Title Doomed Star Eta Carinae
Explanation Eta Carinae may be about to explode. But no one knows when - it may be next year, it may be one million years from now. Eta Carinae [ http://antwrp.gsfc.nasa.gov/apod/ap991011.html ]'s mass - about 100 times greater than our Sun [ http://antwrp.gsfc.nasa.gov/apod/sun.html ] - makes it an excellent candidate for a full blown supernova [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/supernovae.html ]. Historical records do show that about 150 years ago Eta Carinae [ http://en.wikipedia.org/wiki/Eta_Carinae ] underwent an unusual outburst that made it one of the brightest stars [ http://www.astro.wisc.edu/%7Edolan/constellations/extra/brightest.html ] in the southern sky [ http://antwrp.gsfc.nasa.gov/apod/ap000618.html ]. Eta Carinae [ http://www.seds.org/messier/xtra/ngc/etacar.html ], in the Keyhole Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap060316.html ], is the only star currently thought to emit natural LASER light [ http://antwrp.gsfc.nasa.gov/apod/ap971129.html ]. This image [ http://www.stsci.edu/pubinfo/PR/96/23/A.html ], taken in 1996, resulted from sophisticated image-processing procedures designed to bring out new details in the unusual nebula that surrounds this rogue star [ http://csep10.phys.utk.edu/guidry/violence/etacarinae.html ]. Now clearly visible are two distinct lobes, a hot central region [ http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1995ApJ...445L.121C ], and strange radial streaks. The lobes are filled with lanes of gas and dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ] which absorb the blue and ultraviolet light [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ] emitted near the center. The streaks remain unexplained. Will these clues tell us how the nebula was formed? [ http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1995ApJ...441L..77F ] Will they better indicate when Eta Carinae [ http://heasarc.gsfc.nasa.gov/docs/objects/heapow/archive/stars/etacar_pspc_19990525.html ] will explode?
X-Ray Stars Of Orion
Title X-Ray Stars Of Orion
Explanation The stars of Orion [ http://astro.caltech.edu/~bbb/paper/star.splitter.html ] shine brightly in northern winter skies where the constellation [ http://www.seds.org/messier/more/oricloud.html ] harbors the closest large stellar nursery, the Great Nebula of Orion [ http://antwrp.gsfc.nasa.gov/apod/ap990522.html ], a mere 1500 light-years away. In fact, the apparently bright clump of stars near the center of this Chandra X-ray telescope [ http://imagine.gsfc.nasa.gov/docs/introduction/ xray_information.html ] picture of a portion of the nebula are the massive stars of the Trapezium [ http://antwrp.gsfc.nasa.gov/apod/ap971118.html ] - the young star cluster which powers much of the nebula's visible-light glow. But the sheer number of other stars seen in this X-ray image [ http://chandra.harvard.edu/photo/cycle1/0054/index.html ], which spans about 10 light-years, has surprised and delighted astronomers and this picture was recently touted [ http://chandra.harvard.edu/press/00_releases/press_011400ori.html ] as the richest field of X-ray sources ever recorded in a single observation. The picture does dramatically illustrate that young stars are prodigious sources of X-rays [ http://antwrp.gsfc.nasa.gov/apod/ap990828.html ], thought to be produced in hot stellar coronas [ http://chandra.harvard.edu/xray_sources/normal_stars.html ] and surface flares in a young star's strong magnetic field. Our middle-aged Sun [ http://antwrp.gsfc.nasa.gov/apod/ap981221.html ] itself was probably thousands of times brighter in X-rays when, like the Trapezium [ http://seds.lpl.arizona.edu/messier/more/m042_more.html ] stars, it was [ http://antwrp.gsfc.nasa.gov/apod/ap990228.html ] only a few million years old. The dark lines through the image are instrumental artifacts.
A GRB 000301C Symphony
Title A GRB 000301C Symphony
Explanation Telescopic instruments in Earth and space are still tracking a tremendous explosion that occurred across the universe. A nearly unprecedented symphony of international observations began abruptly on March 1 when Earth-orbiting RXTE [ http://heasarc.gsfc.nasa.gov/docs/xte/xte_1st.html ], Sun-orbiting Ulysses [ http://helio.estec.esa.nl/ulysses/ ], and asteroid-orbiting NEAR [ http://near.jhuapl.edu/Education/intro/NEARintro.html ] all detected [ http://gcn.gsfc.nasa.gov/gcn/gcn3/568.gcn3 ] a 10-second burst [ http://antwrp.gsfc.nasa.gov/apod/ap991104.html ] of high-frequency gamma radiation [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ]. Within 48 hours astronomers using the 2.5-meter Nordic Optical Telescope [ http://www.astro.lu.se/not.html ] chimed in with the observation of a middle-frequency optical counterpart [ http://antwrp.gsfc.nasa.gov/apod/ap970407.html ] that was soon confirmed with the 3.5-meter Calar Alto Telescope [ http://www.mpia-hd.mpg.de/Public/CAHA/ ] in Spain. By the next day the explosion was picked up in low-frequency radio waves [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/emspectrum.html ] by the by the European IRAM [ http://www.iram.es/ ] 30-meter dish in Spain, and then by the VLA [ http://info.aoc.nrao.edu/doc/vla/html/VLAintro.shtml ] telescopes in the US. The Japanese 8-meter Subaru Telescope [ http://www.subaru.naoj.org/Introduction/outline.html ] interrupted a maiden engineering test [ http://gcn.gsfc.nasa.gov/gcn/gcn3/577.gcn3 ] to trumpet in infrared [ http://www.ipac.caltech.edu/Outreach/Edu/discovery.html ] observations. Major telescopes across the globe soon began playing along as GRB 000301C came into view, detailing unusual behavior [ http://gcn.gsfc.nasa.gov/gcn/gcn3/599.gcn3 ]. The Hubble Space Telescope [ http://www.stsci.edu/hst/ ] captured the above image [ http://www-int.stsci.edu/~fruchter/GRB/000301C/ ] and was the first to obtain [ http://gcn.gsfc.nasa.gov/gcn/gcn3/603.gcn3 ] an accurate distance to the explosion, placing it near redshift 2, most of the way across the visible universe. The Keck II Telescope [ http://www2.keck.hawaii.edu:3636/realpublic/gen_info/gen_info.html ] in Hawaii quickly confirmed and refined [ http://gcn.gsfc.nasa.gov/gcn/gcn3/605.gcn3 ] the redshift. Still, no one is sure what type of explosion [ http://antwrp.gsfc.nasa.gov/apod/ap980508.html ] this was. The symphony is not over - oddly no host galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap990210.html ] appears near the position of this explosion. Will one appear as the din of the loud fireball fades [ http://antwrp.gsfc.nasa.gov/apod/ap970917.html ]?
Star Clouds over Arizona
Title Star Clouds over Arizona
Explanation The clouds in the foreground are much different than the clouds in the background. In the foreground are a photogenic deck of Earth-based water clouds [ http://en.wikipedia.org/wiki/Clouds ]. The long exposure used to create the above photograph [ http://www.analemma.de/english/desrtsky.html ] makes the light from the left, reflected from Phoenix [ http://en.wikipedia.org/wiki/Phoenix%2C_Arizona ], Arizona [ http://en.wikipedia.org/wiki/Arizona ], USA [ http://www.cia.gov/cia/publications/factbook/geos/us.html ], appear like a sunset [ http://antwrp.gsfc.nasa.gov/apod/ap980526.html]. Far in the distance, however, are star clouds from the disk of our Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap050605.html ]. Billions of stars like our Sun live there, circling our Galactic center every 200 million years. Contrast between the water clouds and the star clouds has been digitally enhanced [ http://www.astropix.com/HTML/J_DIGIT/ETHICS.HTM ]. Between the two, visible on the upper right, is the planet Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap050911.html ].
NGC 2440: Cocoon of a New Wh …
Title NGC 2440: Cocoon of a New White Dwarf
Explanation Like a butterfly, a white dwarf star begins its life by casting off a cocoon that enclosed its former self. In this analogy, however, the Sun would be a caterpillar and the ejected shell of gas would become the prettiest of all! In the above cocoon [ http://hubblesite.org/newscenter/newsdesk/archive/releases/1999/35/image/e ], the planetary nebula designated NGC 2440, contains one of the hottest white dwarf stars known. The white dwarf [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.html ] can be seen as the bright dot near the photo's center. Our Sun will eventually become a "white dwarf butterfly", but not for another 5 billion years. The above false color image [ http://heritage.stsci.edu/1999/38/ ] was post-processed by Forrest Hamilton [ http://heritage.stsci.edu/commonpages/infoindex/ourproject/f_hamilton.html ].
Skylab Over Earth
Title Skylab Over Earth
Explanation Skylab [ http://www-pao.ksc.nasa.gov/history/skylab/skylab.htm ] was an orbiting laboratory launched by a Saturn V rocket [ http://antwrp.gsfc.nasa.gov/apod/ap010525.html ] in May 1973. Skylab [ http://heasarc.gsfc.nasa.gov/docs/heasarc/missions/images/skylab_images.html ], pictured above [ http://grin.hq.nasa.gov/ABSTRACTS/GPN-2000-001055.html ], was visited three times by NASA astronauts who sometimes stayed as long as two and a half months. Many scientific tests were performed on Skylab [ http://www.ssl.msfc.nasa.gov/ssl/pad/solar/skylab.htm ], including astronomical observations in ultraviolet [ http://imagers.gsfc.nasa.gov/ems/uv.html ] and X-ray [ http://cxpi.spme.monash.edu.au/xray_history.htm ] light. Some of these observations yielded valuable information about Comet Kohoutek [ http://en.wikipedia.org/wiki/Kohoutek ], our Sun [ http://www.nineplanets.org/sol.html ] and about the mysterious X-ray background [ http://antwrp.gsfc.nasa.gov/apod/ap000114.html ] - radiation that comes from all over the sky. Skylab [ http://en.wikipedia.org/wiki/Skylab ] fell back to earth on 11 July 1979.
The Solar Spectrum
Title The Solar Spectrum
Explanation It is still not known why the Sun's light is missing some colors. Shown above are all the visible [ http://imagers.gsfc.nasa.gov/ems/visible.html ] colors of the Sun [ http://www.seds.org/nineplanets/nineplanets/sol.html ], produced by passing the Sun's light through a prism [ http://en.wikipedia.org/wiki/Prism_%28optics%29 ]-like device. The above spectrum [ http://www.noao.edu/image_gallery/html/im0600.html ] was created at the McMath-Pierce [ http://www.noao.edu/kpno/40th/mcpierce.html ] Solar Observatory [ http://antwrp.gsfc.nasa.gov/apod/ap960315.html ] and shows, first off, that although our yellow-appearing Sun [ http://antwrp.gsfc.nasa.gov/apod/sun.html ] emits light of nearly every color [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ], it does indeed appear brightest in yellow-green light. The dark patches in the above spectrum [ http://www.noao.edu/image_gallery/html/im0600.html ] arise from gas at or above the Sun's surface [ http://antwrp.gsfc.nasa.gov/apod/ap000110.html ] absorbing sunlight emitted below. Since different types of gas absorb different colors of light [ http://csep10.phys.utk.edu/astr162/lect/light/absorption.html ], it is possible to determine what gasses compose the Sun. Helium [ http://en.wikipedia.org/wiki/Helium ], for example, was first discovered [ http://www-solar.mcs.st-andrews.ac.uk/~clare/Lockyer/helium.html ] in 1870 on a solar spectrum and only later found [ http://en.wikipedia.org/wiki/Helium ] here on Earth. Today, the majority of spectral absorption lines [ http://csep10.phys.utk.edu/astr162/lect/sun/composition.html ] have been identified - but not all [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1995ApJS..100..473K ].
Simulated Gamma-ray Sky
Title Simulated Gamma-ray Sky
Explanation Scheduled for launch in 2007, the Gamma-ray Large Area Space Telescope [ http://glast.gsfc.nasa.gov/public/ ] (GLAST) will explore the Universe in gamma-rays [ http://cossc.gsfc.nasa.gov/docs/cgro/epo/vu/ index.html ], the most energetic form of light. To get ready, consider this dynamic gamma-ray sky animation - constructed from simulating the first 55 days (seen above at one frame per day) of GLAST observations of cosmic gamma-ray sources. The all-sky view is projected in an astronomical (RA-Dec) coordinate [ http://www.astronomynotes.com/nakedeye/s6.htm ] system that shows the plane of our Milky Way Galaxy as a broad U-shape, with the center of the galaxy toward the right. So what shines in this gamma-ray sky [ http://antwrp.gsfc.nasa.gov/apod/ap020112.html ]? Besides the diffuse Milky Way glow, astronomers testing their skills on the simulated data have found flaring active galaxies [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/ active_galaxies.html ], pulsars [ http://antwrp.gsfc.nasa.gov/apod/ap010602.html ], gamma-ray bursts [ http://www.pbs.org/wgbh/nova/gamma/milkyway.html ], the flaring Sun [ http://hesperia.gsfc.nasa.gov/hessi/flares.htm ], and of course, the gamma-ray Moon [ http://antwrp.gsfc.nasa.gov/apod/ap060527.html ].
GRO J1655-40: Evidence for a …
Title GRO J1655-40: Evidence for a Spinning Black Hole
Explanation In the center of a swirling whirlpool of hot gas is likely a beast that has never been seen directly: a black hole [ http://cosmology.berkeley.edu/Education/BHfaq.html ]. Studies of the bright light emitted by the swirling gas [ http://antwrp.gsfc.nasa.gov/apod/ap980723.html ] frequently indicate not only that a black hole [ http://antwrp.gsfc.nasa.gov/htmltest/rjn_bht.html ] is present, but also likely attributes. The gas surrounding GRO J1655-40, for example, has been found to display an unusual flickering [ http://www.sciencedaily.com/releases/2001/05/010502075229.htm ] at a rate of 450 times a second. Given a previous mass estimate [ http://adsabs.harvard.edu/cgi-bin/bib_query?1997ApJ...477..876O ] for the central object [ http://chandra.harvard.edu/resources/illustrations/blackholesStorm.html ] of seven times the mass of our Sun [ http://antwrp.gsfc.nasa.gov/apod/sun.html ], the rate of the fast flickering [ http://arxiv.org/abs/astro-ph/0001167 ] can be explained [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2001ApJ...552L..49S ] by a black hole [ http://antwrp.gsfc.nasa.gov/apod/black_holes.html ] that is rotating [ http://astrosun.tn.cornell.edu/courses/astro201/ergosphere.htm ] very rapidly. What physical mechanisms actually cause the flickering [ http://heasarc.gsfc.nasa.gov/docs/xte/learning_center/discover_0896.html ] -- and a slower quasi-periodic oscillation [ http://imagine.gsfc.nasa.gov/docs/features/news/12jul96.html ] (QPO) -- in accretion disks [ http://antwrp.gsfc.nasa.gov/apod/ap991219.html ] surrounding black holes [ http://antwrp.gsfc.nasa.gov/apod/ap010119.html ] and neutron stars [ http://www.astro.umd.edu/~miller/nstar.html ] remains a topic of much research.
Exploring Comet Tails
Title Exploring Comet Tails
Explanation Comets [ http://seds.lpl.arizona.edu/billa/tnp/comets.html ] are known for their tails. In the spring [ http://antwrp.gsfc.nasa.gov/apod/ap970320.html ] of 1997 and 1996 Comet Hale-Bopp [ http://encke.jpl.nasa.gov/hale_bopp_info.html ] (above) and Comet Hyakutake [ http://encke.jpl.nasa.gov/comets_long/96B2.html ] gave us stunning examples [ http://pages.prodigy.net/pam.orman/JoeGallery.html ] as they passed near the Sun. These extremely active comets [ http://antwrp.gsfc.nasa.gov/apod/ap980410.html ] were bright, naked-eye spectacles offering researchers an opportunity to telescopically [ http://encke.jpl.nasa.gov/ ] explore the composition of primordial chunks of our solar system by studying their long and beautiful tails. But it has only recently been discovered that surprising readings [ ftp://ftp.hq.nasa.gov/pub/pao/pressrel/2000/00-055.txt ] from experiments on-board the interplanetary Ulysses probe [ http://ulysses.jpl.nasa.gov ] which lasted for several hours on May 1, 1996, indicate the probe passed through [ http://www.sp.ph.ic.ac.uk/Ulysses/comet/ ] comet Hyakutake's tail! Ulysses experiments were intended [ http://ulysses.jpl.nasa.gov/science/objectives.html ] to study the Sun and solar wind and the spacecraft-comet [ http://stardust.jpl.nasa.gov/ ] encounter was totally unanticipated. Relative positions of Ulysses [ http://ulysses-ops.jpl.esa.int/ulysses/ ] and Hyakutake on that date indicate that this comet's ion tail [ http://antwrp.gsfc.nasa.gov/apod/ap960319.html ] stretched an impressive 360 million miles or about four times the Earth-Sun distance [ http://antwrp.gsfc.nasa.gov/apod/ap981212.html ]. This makes Hyakutake's tail the longest ever recorded [ http://heasarc.gsfc.nasa.gov/docs/heasarc/missions/isee3.html ] and suggests that comet tails [ http://antwrp.gsfc.nasa.gov/apod/ap960327.html ] are much longer than previously believed.
Gamma-Ray Moon
Title Gamma-Ray Moon
Explanation If you could see gamma rays [ http://antwrp.gsfc.nasa.gov/apod/ap000722.html ] - photons with a million or more times the energy of visible light - the Moon would appear brighter than the Sun! The startling notion is demonstrated by this image of the Moon from the Energetic Gamma Ray Experiment Telescope (EGRET [ http://cossc.gsfc.nasa.gov/docs/cgro/cgro/egret.html ]) in orbit on NASA's Compton Gamma Ray Observatory [ http://cossc.gsfc.nasa.gov/docs/cgro/index.html ] from April 1991 to June 2000. Then, the most sensitive instrument of its kind, even EGRET could not see the quiet Sun which is extremely faint at gamma-ray energies. So why [ http://www.aas.org/publications/baas/v28n4/aas189/abs/ S025002.html ] is the Moon bright? High energy charged particles, known as cosmic rays [ http://imagine.gsfc.nasa.gov/docs/features/topics/snr_group/ cosmic_rays.html ], constantly bombard the unprotected lunar surface generating gamma-ray photons. EGRET's gamma-ray vision [ http://cossc.gsfc.nasa.gov/docs/cgro/epo/vu/ index.html ] was not sharp enough to resolve a lunar disk or any surface features, but its sensitivity reveals the induced gamma-ray [ http://antwrp.gsfc.nasa.gov/apod/ap050331.html ] moonglow. So far unique [ http://glast.gsfc.nasa.gov/ ], the image was generated from eight exposures made during 1991-1994 and covers a roughly 40 degree wide field of view with gamma-ray intensity represented in false color.
Dark Sun Sizzling
Title 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.
The Galactic Center in Infra …
Title The Galactic Center in Infrared
Explanation The center of our Galaxy is a busy place. In visible light [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/emspectrum.html ], much of the Galactic Center [ http://antwrp.gsfc.nasa.gov/apod/ap011229.html ] is obscured by opaque dust [ http://antwrp.gsfc.nasa.gov/apod/ap030706.html ]. In infrared light [ http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ir_tutorial/discovery.html ], however, dust glows more and obscures less, allowing nearly one million stars to be recorded in the above photograph [ http://www.ipac.caltech.edu/2mass/gallery/images_misc.html ]. The Galactic Center [ http://antwrp.gsfc.nasa.gov/apod/ap020803.html ] itself appears [ http://antwrp.gsfc.nasa.gov/apod/ap020707.html ] on the right and is located about 30,000 light years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] away towards the constellation of Sagittarius [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Sagittarius.html ]. The Galactic Plane [ http://antwrp.gsfc.nasa.gov/apod/ap000130.html ] of our Milky Way Galaxy [ http://www.damtp.cam.ac.uk/user/gr/public/gal_milky.html ], the plane in which the Sun [ http://antwrp.gsfc.nasa.gov/htmltest/gifcity/interv.html ] orbits, is identifiable by the dark diagonal dust lane [ http://antwrp.gsfc.nasa.gov/apod/ap020703.html ]. The absorbing dust [ http://nedwww.ipac.caltech.edu/level5/Mathis/Mathis1.html ] grains are created in the atmospheres of cool red-giant stars [ http://www.historyoftheuniverse.com/starold.html ] and grow in molecular cloud [ http://antwrp.gsfc.nasa.gov/apod/ap030202.html ]s. The region directly surrounding the Galactic Center [ http://antwrp.gsfc.nasa.gov/apod/ap000422.html ] glows brightly in radio [ http://antwrp.gsfc.nasa.gov/apod/ap020521.html ] and high-energy radiation [ http://antwrp.gsfc.nasa.gov/apod/ap000819.html ], and is thought to house a large black hole [ http://hubblesite.org/discoveries/black_holes/home.html ].
Skylab Over Earth
Title Skylab Over Earth
Explanation Skylab [ http://heasarc.gsfc.nasa.gov/docs/heasarc/missions/skylab.html ] was an orbiting laboratory launched by a Saturn V rocket [ http://antwrp.gsfc.nasa.gov/apod/ap950829.html ] in May 1973. Skylab [ http://heasarc.gsfc.nasa.gov/docs/heasarc/missions/images/skylab_images.html ] was visited three times by NASA astronauts who sometimes stayed as long as two and a half months. Many scientific tests were performed on Skylab [ http://www.ssl.msfc.nasa.gov/ssl/pad/solar/skylab.htm ], including astronomical observations in ultraviolet [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#uv ] and X-ray [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#X-ray ] light. Some of these observations yielded valuable information about Comet Kohoutek [ http://www.exploratorium.edu/exploring/space/kohoutek.html ], our Sun [ http://antwrp.gsfc.nasa.gov/apod/ap960916.html ] and about the mysterious X-ray background [ http://antwrp.gsfc.nasa.gov/apod/ap000114.html ] - radiation that comes from all over the sky. Skylab [ http://www.xmission.com/~skylab/skylab.html ] fell back to earth on 11 July 1979.
Sungrazer
Title Sungrazer
Explanation Arcing toward a fiery fate, this Sungrazer comet was recorded by [ http://sohowww.nascom.nasa.gov/gallery/LASCO/las013.cap ] the SOHO spacecraft's Large Angle Spectrometric COronagraph [ http://lasco-www.nrl.navy.mil/aaas/aaas_press_release.html ] (LASCO) on Dec. 23rd, 1996. LASCO [ http://sohowww.nascom.nasa.gov/gallery/LASCO/index.html ] uses an occulting disk, partially visible at the lower right, to block out the otherwise overwhelming solar disk [ http://antwrp.gsfc.nasa.gov/apod/ap960518.html ] allowing it to image the inner 5 million miles of the relatively faint corona [ http://sohowww.nascom.nasa.gov/descriptions/mission/english/ wind_and_corona.html ]. The comet [ http://comets.amsmeteors.org/ ] is seen as its coma [ http://antwrp.gsfc.nasa.gov/apod/ap961219.html ] enters the bright equatorial solar wind region [ http://antwrp.gsfc.nasa.gov/apod/ap000318.html ] (oriented vertically). Spots and blemishes on the image are background stars and camera streaks caused by charged particles. Positioned in space to continuously observe the Sun, SOHO [ http://sohowww.nascom.nasa.gov/descriptions/mission/english/page1.html ] has detected 7 sungrazing comets. Based on their orbits, they are believed to belong to a family of comets created by successive break ups from a single large parent comet [ http://antwrp.gsfc.nasa.gov/apod/ap990814.html ] which passed very near the sun in the twelfth century. The bright comet of 1965, Ikeya-Seki, [ http://comets.amsmeteors.org/comets/lcomets/1965s1.html ] was also a member of the Sungrazer family [ http://comets.amsmeteors.org/comets/sungrazer.html ], coming within about 400,000 miles of the Sun's surface. Passing so close to the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap981212.html ], Sungrazers are subjected to destructive tidal forces along with intense solar heat. This comet, known as SOHO 6, did not survive.
NGC 6888: A Tricolor Starfie …
Title NGC 6888: A Tricolor Starfield
Explanation NGC 6888 [ http://www.noao.edu/image_gallery/html/im0834.html ], also known as the Crescent Nebula, is a cosmic bubble [ http://arxiv.org/abs/astro-ph/0310311 ] about 25 light-years across, blown by winds [ http://www.sdsc.edu/GatherScatter/GSwinter97/owocki.html ] from its central, bright, massive star. Near the center of this intriguing widefield view of interstellar gas clouds and rich star fields [ http://antwrp.gsfc.nasa.gov/apod/ap031023.html ] of the constellation Cygnus, NGC 6888 is about 5,000 light-years away. The three color composite [ http://dg-imaging.astrodon.com/gallery/ display.cfm?imgID=56 ] image was created by stacking exposures through narrow band filters that transmit the light [ http://hubblesite.org/sci.d.tech/behind_the_pictures/ meaning_of_color/eagle.shtml ] from atoms in the clouds. Hydrogen is shown as green, sulfur as red, and oxygen as blue. NGC 6888's central star is classified as a Wolf-Rayet star [ http://www.peripatus.gen.nz/Astronomy/WolRaySta.html ] (WR 136) and is shedding its outer envelope in a strong stellar wind, ejecting the equivalent of our Sun's mass every 10,000 years. Burning fuel at a prodigious rate and near the end of its stellar life [ http://heasarc.gsfc.nasa.gov/docs/xmm_lc/edu/lessons/ background-lifecycles.html ], this star should ultimately go out with a bang in a spectacular supernova explosion [ http://antwrp.gsfc.nasa.gov/apod/ap060430.html ].
Cosmic Rays
Title Cosmic Rays
Explanation Have you ever been hit by a beam of high energy particles from above? Surely you have -- it happens all of the time. Showers of high energy particles occur when energetic cosmic rays [ http://www.srl.caltech.edu/personnel/dick/ cos_encyc.html ] strike the top of the Earth's atmosphere. Cosmic rays were discovered unexpectedly [ http://helios.gsfc.nasa.gov/ hist_1900.html ] in 1912. It is now known that most cosmic rays are atomic nuclei [ http://en.wikipedia.org/wiki/Atomic_nucleus ]. Most are hydrogen [ http://periodic.lanl.gov/elements/1.html ] nuclei, some are helium [ http://periodic.lanl.gov/elements/2.html ] nuclei, and the rest heavier elements. The relative abundance changes with cosmic ray energy -- the highest energy cosmic rays tend to be heavier nuclei. Although many of the low energy cosmic rays [ http://en.wikipedia.org/wiki/Cosmic_rays ] come from our Sun, the origins of the highest energy cosmic rays remains unknown and a topic of much research. This drawing [ http://universe.nasa.gov/be/library/ images-library4.html ] illustrates air showers [ http://www.mpi-hd.mpg.de/hfm/CosmicRay/Showers.html ] from very high energy cosmic rays [ http://helios.gsfc.nasa.gov/ ]. Cosmic rays [ http://www.auger.org/qa/qa.html ] may even be important [ http://www.fnal.gov/pub/inquiring/matter/whysupport/index.html ] to Earth's weather -- common lightning [ http://antwrp.gsfc.nasa.gov/apod/ap040818.html ] may be triggered by passing cosmic rays.
Vela Pulsar: Neutron Star-Ri …
Title Vela Pulsar: Neutron Star-Ring-Jet
Explanation This stunning image [ http://chandra.harvard.edu/photo/cycle1/vela/ ] from the orbiting Chandra X-ray Observatory [ http://chandra.harvard.edu/index.html ] is centered on the Vela pulsar -- the collapsed stellar core within the Vela supernova remnant [ http://antwrp.gsfc.nasa.gov/apod/ap960612.html ] some 800 light-years distant. The Vela pulsar is a neutron star [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/ pulsars.html ]. More massive than the Sun, it has the density of an atomic nucleus. About 12 miles in diameter it spins 10 times a second as it hurtles through the supernova debris cloud [ http://antwrp.gsfc.nasa.gov/apod/ap980425.html ]. The pulsar's [ http://www.jb.man.ac.uk/~pulsar/Education/Sounds/ sounds.html ] electric and magnetic fields accelerate particles to nearly the speed of light, powering the compact x-ray [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/ history1_xray.html ] emission nebula revealed in the Chandra picture. The cosmic crossbow shape is over 0.2 light-years across, composed of an arrow-like jet emanating from the polar region of the neutron star [ http://astro.uchicago.edu/home/web/miller/nstar.html ] and bow-like inner and outer arcs believed to be the edges of tilted rings of x-ray emitting high energy particles. Impressively, the swept back compact nebula indicates the neutron star is moving up and to the right in this picture, exactly along the direction of the x-ray jet. The Vela pulsar (and associated supernova remnant [ http://www.seds.org/billa/twn/velax.html ]) was created by a massive star which exploded over 10,000 years ago. Its awesome x-ray rings and jet are reminiscent of another well-known pulsar powered system, the Crab Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap990929.html ].
M101: An Ultraviolet View
Title M101: An Ultraviolet View
Explanation This picture of giant spiral galaxy Messier 101 (M101) [ http://www.seds.org/messier/m/m101.html ] was taken by the Ultraviolet Imaging Telescope [ http://hypatia.gsfc.nasa.gov/astro/uit/uit.html ] (UIT). UIT [ http://hypatia.gsfc.nasa.gov/astro/uit/uitcutaway.html ] flew into orbit as part of the Astro 2 mission [ http://www.ksc.nasa.gov/shuttle/missions/sts-67/mission-sts-67.html ] on-board the Space Shuttle Endeavour in March 1995. The image has been processed [ http://trifle.gsfc.nasa.gov/UIT/Astro2/Astro2_pictures.html ] so that the colors (dark purple through white) represent an increasing intensity of ultraviolet light [ http://imagine.gsfc.nasa.gov/docs/introduction/ emspectrum.html ]. Pictures of galaxies like this one show mainly clouds of gas containing newly formed stars many times more massive than the sun, which glow strongly in the ultraviolet. In contrast, visible light pictures of galaxies [ http://www.seds.org/messier/more/m101_more.html ] tend to be dominated by the yellow and red light of older stars. Ultraviolet light [ http://titan.srrb.noaa.gov/UV/ ], invisible to the human eye, is blocked by ozone in the atmosphere [ http://jwocky.gsfc.nasa.gov/ ] so ultraviolet pictures of celestial objects must be taken from space. M101 is a mere 22 million light-years away in the constellation Ursa Major [ http://www.seds.org/Maps/Stars_en/Fig/ursamajor.html ]. Its popular moniker is the Pinwheel Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap970805.html ].
M27: Not A Comet
Title M27: Not A Comet
Explanation While searching the skies above 18th century France for comets, astronomer Charles Messier [ http://www.seds.org/messier/xtra/history/biograph.html ] diligently recorded this object as number 27 on his list of things which are definitely not comets [ http://antwrp.gsfc.nasa.gov/apod/ap960626.html ]. So what is it? Well, 20th century astronomers would classify it as a Planetary Nebula [ http://www.seds.org/messier/planetar.html ] ... but it's not a planet either, even though it may appear round [ http://antwrp.gsfc.nasa.gov/apod/ap030614.html ] and planet-like in a small telescope. Messier 27 (M27) is now known to be an excellent example of a gaseous emission nebula [ http://www.astro.washington.edu/balick/WFPC2/ ] created as a sun-like star runs out [ http://antwrp.gsfc.nasa.gov/apod/ap050123.html ] of nuclear fuel in its core. The nebula forms as the star's outer layers are expelled into space, with a visible glow generated by atoms excited by the dying star's intense but invisible ultraviolet light [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/ emspectrum.html ]. Known by the popular name of the Dumbbell Nebula [ http://www.seds.org/messier/m/m027.html ], the beautifully symmetric interstellar gas cloud is about 1,200 light-years away in the constellation Vulpecula [ http://hawastsoc.org/deepsky/vul/index.html ]. This intriguing color composite view [ http://www.ricksastro.com/DSOs/m27HaOiii.shtml ] was recorded through narrow band filters sensitive to emission from hydrogen atoms (shown in red) and oxygen atoms (shown in blue/green).
Solstice Celebration
Title Solstice Celebration
Explanation Season's greetings! At 01:48 Universal Time [ http://aa.usno.navy.mil/AA/faq/docs/UT.html ] on June 21 the Sun reaches [ http://www.archaeoastronomy.com/index.html ] its northernmost point in planet Earth's sky marking [ http://aa.usno.navy.mil/AA/data/docs/EarthSeasons.html ] a season change [ http://www-spof.gsfc.nasa.gov/stargaze/Sseason.htm ] and the first solstice of the year 2000. In celebration [ http://www.lalc.k12.ca.us/laep/smart/Sunrise/ k3les4.html ], consider [ http://www.lalc.k12.ca.us/laep/smart/Sunrise/ k3les1.html ] this delightfully detailed, brightly colored image of the active Sun [ http://antwrp.gsfc.nasa.gov/apod/ap000608.html ]. From the EIT instrument [ http://umbra.nascom.nasa.gov/eit/ ] onboard the space-based SOHO observatory, the tantalizing picture is a false-color composite of three images all made in extreme ultraviolet light. Each individual image [ http://umbra.nascom.nasa.gov/eit/eit_full_res.html ] highlights a different temperature [ http://www.smv.org/jims/ ] regime in the upper solar atmosphere and was assigned a specific color, red at 2 million, green at 1.5 million, and blue at 1 million degrees C. The combined image shows bright [ http://www.solarmax2000.com/ ] active regions strewn across the solar disk, which would otherwise appear as dark groups of sunspots in visible light images, along with some magnificent plasma loops and an immense prominence at the righthand solar limb.
Active Regions, CMEs, and X- …
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/ ].
Ultraviolet Earth from the M …
Title Ultraviolet Earth from the Moon
Explanation Here's a switch: the above picture is of the " Earth " taken from a " lunar " observatory! [ http://antwrp.gsfc.nasa.gov/apod/ap960608.html ] This false color picture [ http://images.jsc.nasa.gov/images/pao/AS16/10075878.htm ] shows how the Earth [ http://antwrp.gsfc.nasa.gov/apod/earth.html ] glows in ultraviolet [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#uv ] (UV) light. UV light is so blue humans can't see it. Very little UV light [ http://titan.srrb.noaa.gov/UV/ ] is transmitted through the Earth's atmosphere but what sunlight does make it through can cause a sunburn [ http://uhs.bsd.uchicago.edu/uhs/infoline/sunburn.htm ]. The Far UV Camera / Spectrograph [ http://cass.jsc.nasa.gov/pub/expmoon/Apollo16/A16_Experiments_UVC.html ] deployed and left on the Moon by the crew of Apollo 16 [ http://antwrp.gsfc.nasa.gov/apod/ap000319.html ] took the above picture. The part of the Earth facing the Sun [ http://antwrp.gsfc.nasa.gov/apod/sun.html ] reflects much UV light, but perhaps more interesting is the side facing away from the Sun. Here bands of UV emission [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/emspectrum.html ] are also apparent. These bands [ http://antwrp.gsfc.nasa.gov/apod/ap970402.html ] are the result of aurorae [ http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_ts?aurora ] and are caused by charged particles [ http://www-spof.gsfc.nasa.gov/Education/Intro.html ] expelled by the Sun.
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