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Iapetus Thermal Radiation Im
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| 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 |
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Iapetus Temperature Variatio
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| 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 |
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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 |
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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 |
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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 |
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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 |
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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 |
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Hubble Finds Mysterious Disk
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Hubble Finds Mysterious Disk of Blue Stars Around Black Hole |
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A Summer View of Russia's Le
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A Summer View of Russia's Lena Delta and Olenek River |
| Description |
These views of the Russian Arctic were acquired by NASA's Multi-angle Imaging SpectroRadiometer (MISR) instrument on July 11, 2004. The brief arctic summer had transformed the frozen tundra and the thousands of lakes, channels, and rivers of the Lena Delta into a fertile wetland, and the usual blanket of thick snow had melted from the vast plains and taiga forests. The images show an area in the northern part of the Sakha Republic in eastern Siberia. The Olenek River wends northeast from the bottom of the images to the upper left, and the delta through which the mighty Lena River empties into the Laptev Sea dominate the top portions of the images. Creating accurate maps of vegetation structure is essential for understanding the seasonal exchanges of energy and water at the Earth's surface and for preserving biodiversity. The left-hand image is a natural-color image from MISR's nadir (vertical-viewing) camera, in which the rivers appear murky due to sediment, and photosynthetically active vegetation appears green. The center image is also from MISR's nadir camera, but is a false-color view in which the predominant red color is due to the brightness of vegetation at near-infrared wavelengths. Apart from the Lena Delta, the most photosynthetically active regions are within the lower half of the image and throughout the great stretch of land that curves across the Olenek River.  The relatively barren ranges of the Volyoi Mountains appear as the pale tan-colored area to the right of image center. The right-hand image is a multiangle, false-color view made from the red band data of the 60-degree-backward, nadir, and 60-degree-forward cameras, displayed as red, green and blue, respectively. Water appears blue in this image because sun glint makes smooth, wet surfaces look brighter at the forward camera's view angle. Much of the landscape and many low clouds appear purple because these surfaces are both forward and backward scattering, and clouds that are further from the surface appear in a different spot for each view angle, creating a rainbow-like appearance. The highly vegetated region in the natural-color nadir image exhibits a faint greenish hue in the multi-angle composite. This subtle effect suggests that the nadir camera is observing more of the brighter, underlying surface than the oblique cameras, providing information about the distribution and density of trees and shrubs in this area. The Multiangle Imaging SpectroRadiometer observes the daylit Earth continuously, and every 9 days views the entire globe between 82 degrees north and 82 degrees south latitude. The MISR Browse Image Viewer [ http://earthobservatory.nasa.gov/cgi-bin/redirect?http://eosweb.larc.nasa.gov/MISRBR/ ], provides access to low-resolution true-color versions of these images. These data products were generated from a portion of the imagery acquired during Terra orbit 24273. The panels cover an area of about 230 kilometers x 420 kilometers, and utilize data from blocks 30 to 34 within World Reference System-2 path 134. MISR was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Earth Science, Washington, DC. The Terra satellite is managed by NASA's Goddard Space Flight Center, Greenbelt, MD. JPL is a division of the California Institute of Technology. Image courtesy NASA/GSFC/LaRC/JPL, MISR Team. [ http://www-misr.jpl.nasa.gov/ ] Text by Clare Averill (Raytheon/JPL). |
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Rice Cultivation in Northwes
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| Title |
Rice Cultivation in Northwest Italy |
| Description |
The lowlands of Lombardy and Piedmont in northwest Italy are some of the most highly developed irrigation areas in the world. Irrigated lands cover at least 160,000 acres in this part of Italy, where rice is the most important crop. These views of the region were acquired on May 8, 2005, by NASA's Multi-angle Imaging SpectroRadiometer (MISR). The multiple viewing angles provided by MISR's nine cameras make it possible to tell wet surfaces, including flooded lands, from other surfaces, and they also make cities easy to locate. The left-hand image is a natural-color view acquired by MISR's downward-looking (nadir) camera, and the right-hand image is a combination of red band data from MISR's 60-degree-backward-, nadir, and 60-degree-forward-viewing cameras. (Red band is what scientists call the "channel" on the sensor that detects red light.) Color changes indicate surface texture, which is influenced by terrain, vegetation structure, soil type, and surface wetness. Wet surfaces or areas with standing water appear in blue or purple-blue hues. The purple-blue areas that dominate the center-left part of the image are part of the extensive irrigation network that exists throughout the plains and meadows of the region. Cities with tall buildings appear in red-orange hues. In this type of image, the city of Milan is the most obvious. The small orange area in the center of the purple inundated area indicates the location of Vercelli, and the larger city of Milan is the orange area to the northeast, on the other side of the Ticino River. To a lesser extent, the cities of Novara, Pavia, Galliate, Mortara, and Vigevano are also identifiable by their orange hues. MISR can tell various surface features like cities or irrigated areas apart because of the way surfaces reflect light. A smooth water surface tends to reflect sunlight away from the Sun. This effect is most apparent when a satellite views the surface with the Sun in front of the camera. Similarly, rough surfaces tend to reflect light back towards the Sun, and this "backward scattering" is most obvious when a satellites views a surface with the Sun behind the camera. Clouds present over the high country to the west of the Lago Maggiore (upper left corner) and along the coast of the Golfo di Genova (bottom) appear in a different spot for each view angle, creating a rainbow-like appearance. Mountains also have a "wavy" look in the multi-angle combination because, like clouds, their height above the surface makes them appear in a different spot in each camera's view angle. The Multi-angle Imaging SpectroRadiometer observes the daylit Earth continuously, viewing the entire globe between 82 degrees North and 82 degrees South latitude every nine days. This image covers an area of about 131 kilometers by 191 kilometers. These data products were generated from a portion of the imagery acquired during Terra orbit 28660 and utilize data from block 54 within World Reference System-2 path 193. MISR was, built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Science Mission Directorate, Washington, DC. The Terra satellite is managed by NASA's Goddard Space Flight Center, Greenbelt, MD. JPL is managed for NASA by the California Institute of Technology. Image courtesy NASA/GSFC/LaRC/JPL, MISR Team. [ http://www-misr.jpl.nasa.gov/ ] Text by Clare Averill (Raytheon ITSS/JPL) |
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First 3-D Vews of the Sun
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First 3-D Vews of the Sun |
| Description |
For millennia, we on Earth have seen the Sun as a flat disk in the sky. Now, for the first time, we are seeing the Sun in three dimensions, thanks to the recently launched twin Solar Terrestrial Relations Observatory (STEREO [ http://stereo.gsfc.nasa.gov/index.shtml ]) spacecraft, which orbit the Sun, one in front of the Earth and one behind the Earth. Just as our two eyes give us a three-dimensional view of the world by providing us with two parallel perspectives, STEREO gives us a three-dimensional view of the Sun by combining views from the two spacecraft. The top image shows a spicule, a long jet of gas, near the Sun's North Pole as seen by a single STEREO instrument on March 20, 2007. The lower image combines the views from both spacecraft as an anaglyph, which shows the Sun in three dimensions when viewed through red and cyan 3-D glasses. [ http://www.nasa.gov/mission_pages/stereo/sun/3D_Glasses.html ] In addition to providing us with new insight into the Sun, this three-dimensional view will help scientists predict when solar storms will hit the Earth. A solar storm can be bad news on Earth. When the solar atmosphere erupts, it blasts billions of tons of electrically charged gas, plasma, into space at a million miles per hour. Called coronal mass ejections, these eruptions can disrupt satellites and electrical systems, overload power lines, and trigger beautifully intense displays of the aurorae—the northern and southern lights—when the magnetic fields in the charged gas interact with Earth's magnetic field. Because coronal mass ejections (CMEs) can be so destructive, it's important to be able to predict when they will hit the Earth."In the solar atmosphere, there are no clues to help us judge distance. Everything appears flat in the 2-D plane of the sky. Having a stereo perspective just makes it so much easier," said Dr. Russell Howard of the Naval Research Laboratory, Washington, the Principal Investigator for the SECCHI (Sun Earth Connection Coronal and Heliospheric Investigation) suite of telescopes on the spacecraft. "Knowing where the front of the CME cloud is will improve estimates of the arrival time from within a day or so to just a few hours," said Howard. "STEREO also will help forecasters estimate how severe the resulting magnetic storm will be." NASA images courtesy the STEREO [ http://stereo.gsfc.nasa.gov/ ] Science Team. |
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M27: Not A Comet
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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). |
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MyCn18: An Hourglass Nebula
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MyCn18: An Hourglass Nebula |
| Explanation |
The sands of time are running out for the central star of this hourglass-shaped planetary nebula [ http://fusedweb.pppl.gov/CPEP/ Chart_Pages/5.Plasmas/Nebula/Planetary.html ]. With its nuclear fuel [ http://fusedweb.pppl.gov/default.html ] exhausted, this brief, spectacular, closing phase of a Sun-like star's life [ http://observe.ivv.nasa.gov/nasa/space/stellardeath/stellardeath_contents.html ] occurs as its outer layers are ejected - its core becoming a cooling, fading White Dwarf [ http://antwrp.gsfc.nasa.gov/apod/ap971102.html ]. Astronomers have recently used the Hubble Space Telescope [ http://hubble.stsci.edu/ ] (HST) to make a series of images of planetary nebulae [ http://antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html ], including the one above [ http://www.stsci.edu/pubinfo/PR/96/07.html ]. Here, delicate rings of colorful glowing gas (nitrogen-red, hydrogen-green, and oxygen-blue) outline the tenuous walls of the "hourglass". The unprecedented sharpness of the HST images has revealed surprising details [ http://www.stsci.edu/pubinfo/gif/Hourgls.txt ] of the nebula ejection process [ http://antwrp.gsfc.nasa.gov/apod/ap960117.html ] and may help resolve the outstanding mystery of the variety of complex shapes and symmetries of planetary nebulae [ http://www.astro.washington.edu/balick/WFPC2/index.html ]. |
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M15: Dense Globular Star Clu
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| Title |
M15: Dense Globular Star Cluster |
| Explanation |
Life might get dull at the core of M15 [ http://antwrp.gsfc.nasa.gov/apod/ap980117.html ] but the sky would always be bright with [ http://starchild.gsfc.nasa.gov/docs/StarChild/ StarChild.html ] stars! In fact, only 40,000 light-years away in the constellation Pegasus, M15 is one of the most densely packed globular star clusters [ http://antwrp.gsfc.nasa.gov/apod/ap000523.html ] in our Milky Way Galaxy. This stunning [ http://heritage.stsci.edu/public/2000aug3/ displayngc7078.html ] Hubble Space Telescope image of M15 [ http://heritage.stsci.edu/public/2000aug3/ ngc7078table.html#facts ] shows thousands of individual stars across the central 10 or so light-years of the cluster, also cataloged as NGC 7078. Yet even the Hubble's sharp vision [ http://hubble.stsci.edu/edu.d.space/ ] can't clearly separate the stars at this cluster's core [ http://xxx.lanl.gov/abs/astro-ph/9512015 ]. Globular star clusters harbor from a hundred thousand up to a million stars and roam the Milky Way [ http://www.rog.nmm.ac.uk/astroweb/mway/index.html ] halo. Like most globulars, M15 is [ http://heritage.stsci.edu/public/2000aug3/ ngc7078.html ] filled with ancient stars, about 12 billion years old compared to the Sun's estimated 4.5 billion years. Its cool red giant stars appear yellowish in this color composite image. Unlike most globulars, M15 displays a planetary nebula [ http://www.astro.washington.edu/balick/WFPC2/ ], the briefly visible gaseous shroud of a dying star. Can you pick [ http://antwrp.gsfc.nasa.gov/apod/ap980415.html ] it out? Cataloged as Kuestner 648, M15's planetary nebula [ http://heritage.stsci.edu/public/2000aug3/ ngc7078table.html#caption ] is the round pinkish cloud at the upper left. |
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October Skylights
| Title |
October Skylights |
| Explanation |
With brilliant Venus [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/ venusfact.html ] above the western horizon at sunset and Jupiter [ http://galileo.jpl.nasa.gov/ ] and Saturn [ http://www.jpl.nasa.gov/cassini/ ] high in the east by early evening, November's night sky is filled with bright planets. October's sky featured bright planets as well and, triggered by the active Sun, some lovely auroral displays [ http://www.exploratorium.edu/learning_studio/ auroras/ ]. This colorful aurora was recorded by astrophotographer Wade Clark in skies above Hamilton, Washington, USA on the night of October 4th. Through the shimmering northern lights [ http://climate.gi.alaska.edu/Curtis/aurora/ aurora.html ] Jupiter and Saturn are easy to spot [ http://antwrp.gsfc.nasa.gov/apod/ap000929.html ] flanking the V-shaped head of Taurus [ http://server.remc12.k12.mi.us/csplanet/myth/ taurus.html ] the Bull. Of course, just above lies the lovely Pleiades star cluster. Solar activity [ http://spaceweather.com/ ] will also produce auroral shows in November, particularly at high northern and southern latitudes. Plus, November skygazers can certainly anticipate a celestial performance on the evening of the 17th/18th -- the moonlit Leonid meteor shower [ http://spacescience.com/headlines/y2000/ast10oct_1.htm ]. |
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M2-9: Wings of a Butterfly N
…
| Title |
M2-9: Wings of a Butterfly Nebula |
| Explanation |
Are stars better appreciated for their art after they die? Actually, stars usually create their most artistic displays "as" they die. In the case of low-mass stars like our Sun [ http://www.seds.org/nineplanets/nineplanets/sol.html ] and M2-9 pictured above [ http://oposite.stsci.edu/pubinfo/PR/97/38/a.html ], the stars transform themselves from normal stars to white dwarfs [ http://antwrp.gsfc.nasa.gov/apod/white_dwarfs.html ] by casting off their outer gaseous envelopes. The expended gas frequently forms an impressive display called a planetary nebula [ http://www.seds.org/messier/planetar.html ] that fades gradually over thousand of years. M2-9 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26A...319..267S ], a butterfly planetary nebula [ http://antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html ] 2100 light-years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] away shown in representative colors, has wings that tell a strange but incomplete tale [ http://oposite.stsci.edu/pubinfo/PR/97/38/pr.html ]. In the center, two stars [ http://antwrp.gsfc.nasa.gov/apod/ap970219.html ] orbit inside a gaseous disk 10 times the orbit of Pluto [ http://antwrp.gsfc.nasa.gov/apod/ap990213.html ]. The expelled envelope of the dying star breaks out from the disk creating the bipolar appearance [ http://antwrp.gsfc.nasa.gov/apod/ap991012.html ]. Much remains unknown about the physical processes that cause planetary nebulae [ http://www.noao.edu/jacoby/pn_gallery.html ]. |
|
Solstice And Season's Eclips
…
| Title |
Solstice And Season's Eclipse |
| Explanation |
Today the Sun reaches its southernmost point [ http://www-spof.gsfc.nasa.gov/stargaze/Sseason.htm ] in planet Earth's sky at 13:37 UT [ http://aa.usno.navy.mil/AA/faq/docs/UT.html ]. This celestial event is known as a solstice, marking the beginning of Summer [ http://antwrp.gsfc.nasa.gov/apod/ap951222.html ] in the Southern Hemisphere and Winter in the North. But this year, the solstice will be followed, on December 25th, by another geocentric celestial event [ http://aa.usno.navy.mil/AA/data/docs/EarthSeasons.html ] -- the last eclipse of the millennium [ http://www.usno.navy.mil/millennium/ ]! The Christmas day eclipse [ http://sunearth.gsfc.nasa.gov/eclipse/extra/ PSE2000Dec25.html ] will only be a partial one as the silhouetted disk of the Moon obscures the Sun's edge. Visible [ http://sunearth.gsfc.nasa.gov/eclipse/SEplot/ SE2000Dec25P.gif ] from much of Canada [ http://sunearth.gsfc.nasa.gov/eclipse/extra/ PSE2000Dec25city2/PSE2000Dec25city2.html ], The United States [ http://sunearth.gsfc.nasa.gov/eclipse/extra/ PSE2000Dec25city1/PSE2000Dec25city1.html ] and Mexico [ http://sunearth.gsfc.nasa.gov/eclipse/extra/ PSE2000Dec25city3/PSE2000Dec25city3.html ], the appearance of the partially eclipsed Sun might remind you of the last holiday cookie [ http://www.cs.cmu.edu/~mjw/recipes/cookies/cookie.html ] you took a bite from. Still, the exact timing and degree of the eclipse will depend very much on your location. This image, from an annular eclipse [ http://www.astrosurf.com/alphaweb/10mai94/ ] in 1994, shows the lunar disk covering around 55% of the Sun's diameter. It is representative of what could be seen from Washington D. C. during the December 25 eclipse maximum which, for that location, occurs at 12:41 PM ET. As always, if you view the eclipse be extremely careful [ http://www.mreclipse.com/Totality/ TotalityCh11.html#Intro ] to protect your eyes. |
|
X-rays From The Cat's Eye
| Title |
X-rays From The Cat's Eye |
| Explanation |
Haunting patterns within planetary nebula NGC 6543 [ http://nineplanets.org/twn/n6543x.html ] readily suggest its popular moniker -- the Cat's Eye nebula. In 1995, a stunning false-color optical image from the Hubble Space Telescope [ http://oposite.stsci.edu/pubinfo/PR/95/01.html ] detailed the swirls of this glowing nebula [ http://www.seds.org/billa/twn/types.html ], known to be the gaseous shroud expelled from a dying sun-like star [ http://observe.ivv.nasa.gov/nasa/space/stellardeath/ stellardeath_opening.html ] about 3,000 light-years from Earth. This composite picture combines the famous Hubble image with new x-ray data [ http://chandra.harvard.edu/xray_astro/ history.html ] from the orbiting Chandra Observatory [ http://chandra.harvard.edu/photo/cycle1/1220/index.html ] and reveals surprisingly intense x-ray emission indicating the presence of extremely hot gas. X-ray emission is shown as blue-purple hues superimposed on red and green optical emission. The nebula's central star itself is clearly immersed in the multimillion degree, x-ray emitting gas. Other pockets of x-ray hot gas seem to be bordered by cooler gas emitting strongly at optical wavelengths, a clear indication that expanding hot gas is sculpting the visible Cat's Eye [ http://antwrp.gsfc.nasa.gov/apod/ap990916.html ] filaments and structures. Gazing into the Cat's Eye, astronomers see the fate of our sun [ http://www.astro.washington.edu/balick/WFPC2/ ], destined to enter its own planetary nebula phase [ http://ad.usno.navy.mil/pne/gallery.html ] of evolution ... in about 5 billion years [ http://chandra.harvard.edu/xray_sources/white_dwarfs.html ]. |
|
CMB Dipole: Speeding Through
…
| Title |
CMB Dipole: Speeding Through the Universe |
| Explanation |
Our Earth [ http://antwrp.gsfc.nasa.gov/apod/ap990131.html ] is not at rest. The Earth moves around the Sun [ http://antwrp.gsfc.nasa.gov/apod/sun.html ]. The Sun orbits the center of the Milky Way Galaxy [ http://antwrp.gsfc.nasa.gov/apod/milky_way.html ]. The Milky Way Galaxy orbits in the Local Group of Galaxies [ http://www.seds.org/messier/more/local.html ]. The Local Group falls toward the Virgo Cluster of Galaxies [ http://antwrp.gsfc.nasa.gov/apod/ap010126.html ]. But these speeds are less than the speed that all of these objects together move relative to the cosmic microwave background [ http://spectrum.lbl.gov/WWW/cmb.html ] (CMB). In the above all-sky map [ http://space.gsfc.nasa.gov/astro/cobe/dmr_image.html ], radiation in the Earth's direction of motion appears blueshifted [ http://imagine.gsfc.nasa.gov/docs/dictionary.html#blueshift ] and hence hotter, while radiation on the opposite side of the sky is redshifted [ http://www.space.com/scienceastronomy/redshift.html ] and colder. The map [ http://map.gsfc.nasa.gov/ ] indicates that the Local Group [ http://www-hpcc.astro.washington.edu/papers/localgroup/lg.html ] moves at about 600 kilometers per second relative to this primordial radiation [ http://www.nap.edu/readingroom/books/cosmology/2.html#CMBR ]. This high speed was initially unexpected and its magnitude is still unexplained. Why are we moving so fast? [ http://zebu.uoregon.edu/~js/glossary/cosmic_microwave_background.html ] What is out there? [ http://antwrp.gsfc.nasa.gov/apod/ap000104.html ] |
|
The Cat's Eye Nebula from Hu
…
| Title |
The Cat's Eye Nebula from Hubble |
| Explanation |
Staring across interstellar space, the alluring Cat's Eye [ http://heritage.stsci.edu/2004/27/] nebula lies three thousand light-years from Earth. A classic planetary nebula [ http://www.seds.org/messier/planetar.html ], the Cat's Eye (NGC 6543) represents a final, brief yet glorious phase [ http://www.astro.washington.edu/balick/WFPC2/ ] in the life of a sun-like star. This nebula's dying central star may have produced the simple, outer pattern of dusty concentric shells [ http://arxiv.org/abs/astro-ph/0401056 ] by shrugging [ http://antwrp.gsfc.nasa.gov/apod/ap011003.html ] off outer layers [ http://antwrp.gsfc.nasa.gov/apod/ap031101.html ] in a series of regular convulsions. But the formation of the beautiful, more complex inner structures is not well understood [ http://antwrp.gsfc.nasa.gov/apod/ap061112.html ]. Seen so clearly in this sharp Hubble [ http://hubblesite.org/newscenter/newsdesk/archive/ releases/2004/27/fastfacts/ ] Space Telescope image, the truly cosmic eye is over half a light-year across. Of course, gazing into the Cat's Eye [ http://antwrp.gsfc.nasa.gov/apod/ap031101.html ], astronomers may well be seeing the fate of our sun, destined to enter its own planetary nebula phase [ http://chandra.harvard.edu/xray_sources/ white_dwarfs.html ] of evolution ... in about 5 billion years [ http://hubblesite.org/newscenter/newsdesk/archive/ releases/1997/38/astrofile/ ]. |
|
Cat's Eye Wide and Deep
| Title |
Cat's Eye Wide and Deep |
| Explanation |
The Cat's Eye Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap070513.html ] (NGC 6543) is one of the best known planetary nebulae [ http://en.wikipedia.org/wiki/Planetary_nebula ] in the sky. Its more familiar outlines are seen in the brighter central region of this impressive wide-angle view [ http://panther-observatory.com/gallery/deepsky/doc/ NGC6543_f10.htm ]. But the composite image also combines many short and long exposures to reveal the nebula's extremely faint halo. At an estimated distance of 3,000 light-years, the faint outer halo is over 5 light-years across. Planetary nebulae [ http://www.noao.edu/jacoby/pn_gallery.html ] have long been appreciated as a final phase in the life [ http://imagine.gsfc.nasa.gov/docs/teachers/lifecycles/ stars.html ] of a sun-like star. More recently, some planetary nebulae are found to have halos [ http://www.ing.iac.es/~rcorradi/HALOES/ ] like this one, likely formed of material shrugged off during earlier episodes in the star's evolution. While the planetary nebula phase [ http://www.astro.washington.edu/balick/WFPC2/ ] is thought to last for around 10,000 years, astronomers estimate the age of the outer filamentary portions of this halo to be 50,000 to 90,000 years. Visible on the right, some 50 million light-years beyond the Cat's Eye, lies spiral galaxy NGC 6552 [ http://www.freelists.org/archives/az-observing/ 06-2003/msg00148.html ]. |
|
NGC 6826: The Blinking Eye
| Title |
NGC 6826: The Blinking Eye |
| Explanation |
The colorful planetary nebula phase [ http://www.astro.washington.edu/balick/WFPC2/ ] of a sun-like star's life is brief [ http://oposite.stsci.edu/pubinfo/PR/97/38/astrofile1.html ]. Almost in the "blink of an eye" - cosmically speaking - the star's outer layers are cast off, forming an expanding emission nebula. This nebula lasts perhaps 10 thousand years compared to a 10 billion year stellar life span. Spectacular planetary nebulae [ http://oposite.stsci.edu/pubinfo/PR/97/38.html ] are familiar objects to both professional and amateur astronomers, but they still contain a few surprises. For instance, the lovely nebula NGC 6826 [ http://www.astro.washington.edu/balick/WFPC2/n6826.caption.html ], also known as the Blinking Eye Nebula, has mysterious red FLIERS [ http://antwrp.gsfc.nasa.gov/apod/ap961122.html ] seen on either side of the Hubble Space Telescope image above. Are they also expanding outward from the central star? If so, their "bow shocks" [ http://antwrp.gsfc.nasa.gov/apod/ap971203.html ] point in the wrong direction! |
|
Solar System Web Cam
| Title |
Solar System Web Cam |
| Explanation |
Ranging throughout the solar system [ http://space.jpl.nasa.gov/ ], these pictures all have something in common. They were taken with an 8 inch diameter telescope, a size popular with amateur astronomy buffs, and slightly modified "web cam" of the type widely used to send images out over the internet. The results are clearly remarkable for [ http://www.djcash.demon.co.uk/astro/webcam/webcam.htm ] such inexpensive and readily available equipment. Each sharp image was produced from 20 to 30 frames which were digitally stacked and processed using free software [ http://utopia.ision.nl/users/rjstek/english/software/ index.htm ]. Until recently, digital imaging for amateur astronomers required a specialized camera [ http://www.wvi.com/~rberry/cookbook.htm ], but the advent of low-light video surveillance cameras and web cams now presents other options for relatively bright [ http://www.astrabio.demon.co.uk/QCUIAG/ac/3dmoon.htm ] solar system objects. Want to try some unconventional [ http://www.astrabio.demon.co.uk/QCUIAG/ ] web cam astronomy? Geoff Chester, Public Affairs Officer at the U.S. Naval Observatory [ http://www.usno.navy.mil ], offers these images and an account of his own adventures [ http://www.usno.navy.mil/pao/QuickCamAstro.shtml ] from a suburban front lawn near Washington D.C. |
|
The Planetary Nebula Show
| Title |
The Planetary Nebula Show |
| Explanation |
What do the Owl, the Cat's Eye, the Ghost of Jupiter, and Saturn have in common? They're all planetary nebulae [ http://ad.usno.navy.mil/pne/ ] of course(!), glowing gaseous shrouds shed by dying sun-like stars as they run out [ http://www.astro.washington.edu/balick/WFPC2/index.html ] of nuclear fuel. Beautiful to look at [ http://www.ucalgary.ca/~zhangc/pnimage.html ], the symmetric, planet-like shapes [ http://www.seds.org/messier/planetar.html ] of these cosmic clouds [ http://www.ipac.caltech.edu/2mass/gallery/ images_pne.html ], typically 1,000 times the size of our solar system [ http://www.cismall.com/deepsky/nebulae.html ], evoke their popular names. Flipping through [ http://www.noao.edu/outreach/aop/observers/ pn.html ] digital pictures made by participants in the Kitt Peak National Observatory Visitor Center's Advanced Observing Program [ http://www.noao.edu/outreach/aop/ ], astronomer Adam Block created [ http://antwrp.gsfc.nasa.gov/apod/ap010427.html ] this delightful animation. Ten different planetary nebula images are presented, each registered on the central star. In order, their catalog designations are NGC 1535 [ http://www.noao.edu/outreach/aop/observers/n1535.html ], NGC 3242 [ http://antwrp.gsfc.nasa.gov/apod/ap970331.html ] (Ghost of Jupiter), NGC 6543 [ http://home.achilles.net/~jtalbot/spectra/ Nebulium.html ] (Cat's Eye), NGC 7009 [ http://antwrp.gsfc.nasa.gov/apod/ap971230.html ] (Saturn Nebula), NGC 2438 [ http://antwrp.gsfc.nasa.gov/apod/ap990305.html ], NGC 6772 [ http://www.noao.edu/outreach/aop/observers/n6772.html ], Abell 39 [ http://antwrp.gsfc.nasa.gov/apod/ap010123.html ], NGC 7139 [ http://www.noao.edu/outreach/aop/observers/n7139.html ], NGC 6781 [ http://www.noao.edu/outreach/aop/observers/n6781.html ], and M97 [ http://www.noao.edu/outreach/aop/observers/ m97.html ] (Owl Nebula). This glorious final phase [ http://oposite.stsci.edu/pubinfo/PR/97/38/ astrofile1.html ] in the life of a star lasts only about 10,000 years. |
|
The Medusa Nebula
| Title |
The Medusa Nebula |
| Explanation |
Braided, serpentine filaments of glowing gas suggest this nebula's popular name, The Medusa Nebula. Also known as Abell 21, this Medusa is an old planetary nebula [ http://www.seds.org/messier/planetar.html ] some 1,500 light-years away in the constellation Gemini [ http://en.wikipedia.org/wiki/Gemini_(constellation) ]. Like its mythological [ http://en.wikipedia.org/wiki/Medusa ] namesake, the nebula is associated with a dramatic transformation. The planetary nebula [ http://www.noao.edu/jacoby/pn_gallery.html ] phase represents a final stage in the evolution [ http://casswww.ucsd.edu/public/tutorial/StevI.html ] of low mass stars like the sun [ http://www.astro.washington.edu/balick/WFPC2/ ], as they transform themselves from red giants to hot white dwarf stars and in the process shrug off their outer layers. Ultraviolet radiation [ http://hyperphysics.phy-astr.gsu.edu/hbase/ems1.html ] from the hot star powers the nebular glow. The Medusa's transforming hot central star is visible in the detailed color image [ http://dg-imaging.astrodon.com/gallery/ display.cfm?imgID=106 ] as the small blue star within the upper half of the overall bright crescent shape [ http://www.noao.edu/outreach/aop/observers/medusa.html ]. Fainter filaments clearly extend above and to the left of the bright crescent region. The Medusa Nebula is estimated to be over 4 light-years across. |
|
Auroras Over Both Earth Pole
…
| Title |
Auroras Over Both Earth Poles |
| Explanation |
Auroras [ http://www.exploratorium.edu/learning_studio/auroras/ ] in the north and south can be nearly mirror images of each other. Such mirroring had been suspected for centuries but dramatically confirmed [ http://eiger.physics.uiowa.edu/%7Evis/conjugate_aurora/ ] only last month by detailed images from NASA [ http://www.nasa.gov/ ]'s orbiting Polar spacecraft [ http://www.geophys.washington.edu/Space/SpaceExp/POLAR/ ]. Pictured above [ http://www.gsfc.nasa.gov/topstory/20011025aurora.html ], a time-lapse movie shows simultaneous changes in aurora borealis [ http://www.imv.uit.no/english/science/publicat/waynorth/wn1/contents.htm ], at the top, and aurora australis [ http://ast.leeds.ac.uk/haverah/spaseman/aurora.shtml ], at the bottom. A cloud of electrons and ions moving out from the Sun on October 22 [ http://www.spaceweather.com/aurora/gallery_21oct01.html ] created [ http://www.spaceweather.com/glossary/imf.html ] the auroras [ http://www-istp.gsfc.nasa.gov/Education/whaur1.html ]. The solar explosion [ http://antwrp.gsfc.nasa.gov/apod/ap000309.html ] that released the particles [ http://www-istp.gsfc.nasa.gov/Education/waurora2.html ] occurred about three days earlier. |
|
M2-9: Wings of a Butterfly N
…
| Title |
M2-9: Wings of a Butterfly Nebula |
| Explanation |
Are stars better appreciated for their art after they die? Actually, stars usually create their most artistic displays "as" they die. In the case of low-mass stars like our Sun [ http://www.nineplanets.org/sol.html ] and M2-9 pictured above [ http://oposite.stsci.edu/pubinfo/PR/97/38/a.html ], the stars transform themselves from normal stars to white dwarfs [ http://antwrp.gsfc.nasa.gov/apod/ap000910.html ] by casting off their outer gaseous envelopes. The expended gas frequently forms an impressive display called a planetary nebula [ http://www.seds.org/messier/planetar.html ] that fades gradually over thousand of years. M2-9 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26A...319..267S ], a butterfly planetary nebula [ http://antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html ] 2100 light-years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] away shown in representative colors, has wings that tell a strange but incomplete tale [ http://oposite.stsci.edu/pubinfo/PR/97/38/pr.html ]. In the center, two stars [ http://antwrp.gsfc.nasa.gov/apod/ap970219.html ] orbit inside a gaseous disk 10 times the orbit of Pluto [ http://antwrp.gsfc.nasa.gov/apod/ap990213.html ]. The expelled envelope of the dying star breaks out from the disk creating the bipolar appearance [ http://antwrp.gsfc.nasa.gov/apod/ap991012.html ]. Much remains unknown about the physical processes that cause planetary nebulae [ http://www.noao.edu/jacoby/pn_gallery.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/ap980518.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/ap980426.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://www.astro.wisc.edu/~dolan/constellations/ constellations/Vulpecula.html ]. This gorgeous synthetic color picture of M27 [ http://www.eso.org/outreach/press-rel/pr-1998/ phot-38-98.html ] was produced during testing of one of the European Southern Observatory's Very Large Telescopes [ http://www.eso.org/outreach/press-rel/pr-1999/ pr-06-99.html ]. |
|
MyCn18: An Hourglass Nebula
| Title |
MyCn18: An Hourglass Nebula |
| Explanation |
The sands of time are running out for the central star of this hourglass-shaped planetary nebula [ http://fusedweb.pppl.gov/CPEP/ Chart_Pages/5.Plasmas/Nebula/Planetary.html ]. With its nuclear fuel [ http://fusedweb.pppl.gov/default.html ] exhausted, this brief, spectacular, closing phase of a Sun-like star's life [ http://www.astro.virginia.edu/class/hawley/astr124/starbirth.html ] occurs as its outer layers are ejected - its core becoming a cooling, fading white dwarf [ http://antwrp.gsfc.nasa.gov/apod/ap000910.html ]. In 1995, astronomers used the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ] (HST) to make a series of images of planetary nebulae [ http://antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html ], including the one above [ http://www.stsci.edu/pubinfo/PR/96/07.html ]. Here, delicate rings of colorful glowing gas (nitrogen [ http://pearl1.lanl.gov/periodic/elements/7.html ]-red, hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ]-green, and oxygen [ http://pearl1.lanl.gov/periodic/elements/8.html ]-blue) outline the tenuous walls of the "hourglass". The unprecedented sharpness of the HST images has revealed surprising details [ http://www.stsci.edu/pubinfo/gif/Hourgls.txt ] of the nebula ejection process [ http://antwrp.gsfc.nasa.gov/apod/ap960117.html ] and may help resolve the outstanding mystery of the variety of complex shapes and symmetries of planetary nebulae [ http://www.astro.washington.edu/balick/WFPC2/index.html ]. |
|
Gomez's Hamburger: A Proto-P
…
| Title |
Gomez's Hamburger: A Proto-Planetary Nebula |
| Explanation |
What, in heaven, is that? Sometimes astronomers [ http://www.aas.org/education/career.html ] see things on the sky they don't immediately understand [ http://antwrp.gsfc.nasa.gov/apod/ap990928.html ]. In 1985 this happened to Arturo Gomez [ http://heritage.stsci.edu/2002/19/bio/bio_gomez_english.html ], and the object became known as Gomez's Hamburger [ http://www.lib.ucdavis.edu/exhibits/food/panel6.html ] for its distinctive yet familiar shape. After some investigation, the object was identified as a proto-planetary nebula [ http://www.astro.washington.edu/palen/Research/nsf/intro.html ], a gas cloud emitted by a Sun [ http://antwrp.gsfc.nasa.gov/apod/sun.html ]-like star just after its central hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ] fuel has all been fused [ http://casswww.ucsd.edu/physics/ph7/StevI.html ] to helium [ http://pearl1.lanl.gov/periodic/elements/2.html ]. Gomez's Hamburger is on its way [ http://instruct1.cit.cornell.edu/courses/astro101/java/evolve/evolve.htm ] to becoming a full-fledged planetary nebula [ http://www.seds.org/messier/planetar.html ] in a few thousand years. The light seen (the bun) is reflected [ http://antwrp.gsfc.nasa.gov/apod/reflection_nebulae.html ] by dust [ http://antwrp.gsfc.nasa.gov/apod/ap990509.html ] from the central star, although the star itself is obscured by a thick dust disk [ http://antwrp.gsfc.nasa.gov/apod/ap000208.html ] that runs across the middle (the patty). Gomez's Hamburger [ http://adsbit.harvard.edu/cgi-bin/nph-iarticle_query?bibcode=1987ApJ...316L..21R ], pictured above [ http://heritage.stsci.edu/2002/19/table.html ] in a recent image from the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap010806.html ], is only a fraction of a light year [ http://www.howstuffworks.com/question94.htm ] across but located approximately 10,000 light years away towards the constellation of Sagittarius [ http://www.astro.wisc.edu/~dolan/constellations/constellations/Sagittarius.html ]. |
|
Meteors and Northern Lights
| Title |
Meteors and Northern Lights |
| Explanation |
Skygazers report [ http://skyandtelescope.com/news/current/ article_696_1.asp ] that the annual Perseid meteor [ http://antwrp.gsfc.nasa.gov/apod/ap020811.html ] shower went pretty much as predicted, producing a meteor [ http://science.nasa.gov/spaceweather/meteors/ gallery_12aug02.html ] every few minutes during the dark early morning hours of August 12 and 13. And as the constellation Perseus [ http://www.astro.wisc.edu/~dolan/constellations/constellations/ Perseus.html ] rose above the horizon on the night of August 11, astrophotographer Wade Clark was anticipating recording images of the flashing meteor trails from the Mt. Baker Ski Area in northwest Washington, USA. But Clark was also treated to a colorful display of northern lights [ http://www.exploratorium.edu/learning_studio/ auroras/ ]. As a result, the stars of Perseus [ http://www.coldwater.k12.mi.us/lms/planetarium/myth/ perseus.html ] are arrayed near the center of his well composed skyscape along with trails of Perseid meteors [ http://comets.amsmeteors.org/meteors/showers/ perseids.html ] all viewed through the auroral glow [ http://www.windows.ucar.edu/spaceweather/ sun_earth8.html ]. The alluring scene might look familiar to watchers of bygone Perseids [ http://antwrp.gsfc.nasa.gov/apod/ap000821.html ]. For many, views of the meteor shower in 2000 [ http://spacescience.com/headlines/y2000/ ast14aug_1.htm ] also coincided with auroral displays, courtesy of the active Sun [ http://www.spaceweather.com/ ]. |
|
Lensing through Baade's Wind
…
| Title |
Lensing through Baade's Window |
| Explanation |
What is the shape and composition of our Milky Way Galaxy [ http://www.astro.washington.edu/strobel/milkyway.description/milkyway.description.html ]? This question would be easier to answer if there wasn't so much obscuring dust [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#dust ]! In the 1940s, however, astronomer Walter Baade [ http://yorty.sonoma.edu/people/faculty/tenn/BM2B.html ] identified a "window" near the center of our Galaxy where there is comparatively little opaque dust. Now called "Baade's Window [ http://www.as.utexas.edu/PIO/SD_scripts/0816.html ]", this sky region contains millions of stars and is used for many studies of the distant Milky Way [ http://antwrp.gsfc.nasa.gov/apod/ap960623.html ]. One clever use, devised by Bohdan Paczynski, is to monitor millions of stars in our Galactic Bulge - many through Baade's window - for sudden brightening [ http://antwrp.gsfc.nasa.gov/apod/ap960202.html ] due to gravitational lensing [ http://www.stsci.edu/EPA/grav_lens.html ]. Current observations by the OGLE [ http://www.astro.princeton.edu/~ogle/warsaw/ ] and MACHO [ http://meteor.anu.edu.au/~pjq/macho.html ] collaborations have now identified dozens of gravitational amplification events. This unexpectedly large number supports previous claims that our Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap960102.html ] has a "bar" of stars across the central nucleus, pointed nearly at the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ]. |
|
Halo of the Cat's Eye
| Title |
Halo of the Cat's Eye |
| Explanation |
The Cat's Eye Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap020324.html ] (NGC 6543) is one of the best known planetary nebulae in the sky [ http://antwrp.gsfc.nasa.gov/apod/ap011003.html ]. Its haunting symmetries [ http://www.cybercom.net/~klb/ tiger.html ] are seen in the very central region of this stunning false-color picture, processed to reveal the enormous but extremely faint halo of gaseous material, over three light-years across, which surrounds the brighter, familiar planetary nebula. Made with data from the Nordic Optical Telescope [ http://www.not.iac.es/ ] in the Canary Islands, the composite picture shows emission from nitrogen atoms as red and oxygen atoms as green and blue shades. Planetary nebulae [ http://www.noao.edu/jacoby/pn_gallery.html ] have long been appreciated as a final phase in the life of a sun-like star. Only much more recently however, have some planetaries been found to have halos [ http://www.ing.iac.es/~rcorradi/HALOES/ ] like this one, likely formed of material shrugged off during earlier active episodes in the star's evolution. While the planetary nebula phase [ http://www.astro.washington.edu/balick/WFPC2/ ] is thought to last for around 10,000 years, astronomers estimate the age of the outer filamentary portions of this halo to be 50,000 to 90,000 years. |
|
Millions of Stars in Omega C
…
| Title |
Millions of Stars in Omega Centauri |
| Explanation |
Pictured above is the largest ball of stars in our Galaxy. About 10 million stars orbit the center of this globular cluster [ http://www.ucolick.org/~mountain/AAA/glob_clusters/globular.html ] - named Omega Centauri [ http://www.astro.lsa.umich.edu:80/users/iotm/dec95/omegacen.html ] - as this giant globular cluster [ http://spacelink.msfc.nasa.gov/Instructional.Materials/Curriculum.Materials/Sciences/Astronomy/Space.Astronomy.Update/Globular.Clusters ] orbits the center of our Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap960213.html ]. Recent evidence indicates that Omega Centauri [ http://www.as.utexas.edu/PIO/SD_scripts/0725.html ] is by far the most massive of the about 160 globular clusters [ http://ast.leeds.ac.uk/research/gcs.html ] in the Milky Way [ http://antwrp.gsfc.nasa.gov/apod/ap950908.html ]. The stars in globular clusters [ http://antwrp.gsfc.nasa.gov/apod/ap951120.html ] are generally older, redder and less massive than our Sun. Studying globular clusters [ http://antwrp.gsfc.nasa.gov/apod/ap951019.html ] tells us about the history of our Galaxy [ http://www.astro.washington.edu/strobel/galaxy.notes/galaxy.notes.html ] and the age of the universe [ http://ast.leeds.ac.uk/research/age.html ]. |
|
The Ion Tail of Comet Hyakut
…
| Title |
The Ion Tail of Comet Hyakutake |
| Explanation |
This picture of Comet Hyakutake [ http://www.eso.org/educnpubrelns/phot-23-96.html ] was taken on March 14, 1996. Structure in the ion tale of Comet Hyakutake [ http://www.astro.washington.edu/astro422/comets.html ] is now clearly visible. An ion tale forms as a comet nears the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ]. Sunlight causes gas and dust to boil off the comet's solid nucleus. Charged gas - called ions - are then accelerated away from the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap951004.html ] by the solar wind [ http://www-spof.gsfc.nasa.gov/Education/wsolwind.html ] - fast moving particles streaming out from the Sun's corona [ http://antwrp.gsfc.nasa.gov/apod/ap951024.html ]. The ion tale will appear blue and glows by fluorescence [ http://charlie.ab.umd.edu/jf/info.html ]. As Comet Hyakutake [ http://cfa-www.harvard.edu/cfa/ps/info1996B2.html ] gets closer to the Sun during the next month, a dust tail is expected to be visible as well. Dust [ http://antwrp.gsfc.nasa.gov/apod/ap960125.html ] tails shine by light reflected from the Sun. Comet tails [ http://antwrp.gsfc.nasa.gov/apod/ap950826.html ] point away from the Sun, even as a comet moves away from the Sun. For observers in the Northern Hemisphere, Comet Hyakutake should appear tonight [ http://encke.jpl.nasa.gov/C1996B2/C1996B2_guide.html ] in the eastern part of the constellation of Virgo and should be about magnitude 2.5. The comet will look the most impressive in the darkest skies - in a city you are likely to see only a fuzzy blob! |
|
A Spiral Galaxy Gallery
| Title |
A Spiral Galaxy Gallery |
| Explanation |
A progression of beautiful spiral galaxies is illustrated above with three photographs from NASA's Ultraviolet Imaging Telescope [ http://fondue.gsfc.nasa.gov/UIT/Astro1/Astro1_pictures.html ] (UIT). Flying above the Earth's obscuring layer of atmosphere on the Space Shuttle Columbia [ http://antwrp.gsfc.nasa.gov/apod/ap950806.html ] during the Astro-1 mission in 1990 [ http://fondue.gsfc.nasa.gov/UIT/UIT_HomePage.html#Astro1 ], UIT's cameras were able to image these distant spirals in the ultraviolet light produced by hot, young stars. These bright stars, newly condensed from gas and dust clouds, give away the location of the spiral arms they are born in. Because they are massive (many times the mass of the Sun), they are shortlived [ http://antwrp.gsfc.nasa.gov/apod/ap951027.html ]. Dying and fading before they move too far from their birth place they make excellent tracers of spiral structure. From left to right the galaxies are known as M33, M74, and M81 and have progressively more tightly wound spiral arms. Astronomers would classify these [ http://sousun1.phys.soton.ac.uk/PH308/galaxies/classification.html ] as Scd, Sc, and Sb type spirals using a galaxy classification scheme [ http://www-hpcc.astro.washington.edu/k12/hubble/hubble.html ] first worked out by Edwin Hubble [ http://antwrp.gsfc.nasa.gov/diamond_jubilee/ d_1996/sandage_hubble.html ]. |
|
Aurora Crown the Earth
| Title |
Aurora Crown the Earth |
| Explanation |
What do aurora look like from space? The POLAR spacecraft [ http://www-star.stanford.edu/~polar/Welcome.html ] answered this by photographing an auroral oval surrounding the north pole of the Earth, causing displays on both the night and day side. The auroral sub-storm, pictured in false-color above [ http://pao.gsfc.nasa.gov/gsfc/images/spacesci/polar/96-37.htm ], developed within 15 minutes and may have lasted as long as on hour. Aurora [ http://antwrp.gsfc.nasa.gov/apod/ap960506.html ] are caused by charged particles streaming away from the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap951004.html ] and towards the Earth [ http://antwrp.gsfc.nasa.gov/apod/ap950629.html ]. As the particles fall to Earth, they spiral along magnetic field lines and cause colorful radiation. The UVI experiment [ http://wwwssl.msfc.nasa.gov/ssl/pad/sppb/UVI/ ] onboard the POLAR spacecraft is equipped with special filters that allow it to see aurora [ http://antwrp.gsfc.nasa.gov/apod/ap951114.html ] in a band of ultraviolet light [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#uv ] where sunlight is relatively dim. The more red the emission depicted in the above photo, the more intense the radiation. Earth's continents have been drawn in for clarity |
|
Superbubbles in the LMC
| Title |
Superbubbles in the LMC |
| Explanation |
Why is there a hole in the center of this nebula? A leading explanation is that it is caused by the stellar winds from the stars that live there. Stars [ http://antwrp.gsfc.nasa.gov/apod/ap960503.html ] - including the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ] - expel electrons, protons, and other charged ions [ http://www-spof.gsfc.nasa.gov/Education/Ielect.html ] in a steady stream - the stellar wind [ http://www-spof.gsfc.nasa.gov/Education/wsolwind.html ]. The wind ions push out the normal hydrogen [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#hydrogen ] and helium [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#helium ] gas found glowing in the nebula. This star forming region is located in the Large Magellanic Cloud [ http://antwrp.gsfc.nasa.gov/apod/ap950918.html ]. This picture [ http://www.astro.lsa.umich.edu:80/users/iotm/may96/n44.html ] is a composite of three separate photographs, each sensitive to only one specific color of light [ http://www.astro.washington.edu/strobel/lightnotes/lightnotes.html ] - a color that distinguishes a specific chemical element [ http://mwanal.lanl.gov/CST/imagemap/periodic/periodic.html ]. It is currently not known why stars emit a stellar wind. |
|
Apollo Sunrise
| Title |
Apollo Sunrise |
| Explanation |
In November of 1969, homeward bound aboard the "Yankee Clipper" command module, the Apollo 12 [ http://antwrp.gsfc.nasa.gov/apod/ap951008.html ] astronauts took this dramatic photograph of the Sun emerging from behind the Earth. From this distant perspective, part of the solar disk peers over the Earth's limb [ http://antwrp.gsfc.nasa.gov/apod/ap951117.html ], its direct light producing the jewel like glint while sunlight scattered by the atmosphere creates the thin bright crescent. Today at 10:24 pm Eastern Daylight [ http://www.ast.cam.ac.uk/RGO/leaflets/summer/summer.html ] Time [ http://www.phys.washington.edu/Department/tour/sundial/ ] is the Summer Solstice [ http://www.lalc.k12.ca.us/laep/smart/Sunrise/k3les1.html ]. From an earthbound perspective [ http://dlt.gsfc.nasa.gov/Ask/lessons/regions/temperate/seasons.html ], the solar disk will climb to its greatest northern declination [ http://www.csbsju.edu/astro/CS/CS.11.html ] marking the Northern Hemisphere's first day of Summer [ http://antwrp.gsfc.nasa.gov/apod/ap951222.html ] and creating the longest day -- with over 15 hours of daylight [ http://nobody.vn.fi/vn/um/kesa3eng.html ] near latitude +40 degrees. |
|
The Equal Night
| Title |
The Equal Night |
| Explanation |
Today the Sun crosses the celestial equator [ http://www.astro.washington.edu/strobel/naked-eye/ naked-eye.html#A1.2.4 ] heading south -- marking the Autumnal Equinox, the first day of Autumn. Equinox means "equal night" and with the Sun on the celestial equator [ http://www.physics.csbsju.edu/astro/CS/CSintro.html ], Earthlings will experience 12 hours of daylight and 12 hours of darkness. Then, for those in the northern hemisphere, the days will begin to grow shorter with the Sun marching [ http://www.lalc.k12.ca.us/laep/smart/Sunrise/k3les1.html ] lower in the sky as winter approaches [ http://www.astro.washington.edu/strobel/naked-eye/ naked-eye.html#A1.2.4.5 ]. A few weeks after the Autumnal Equinox of 1994, the Crew of the Shuttle Endeavor [ http://antwrp.gsfc.nasa.gov/apod/ap950807.html ] recorded this image [ http://images.jsc.nasa.gov/images/pao/STS68/20172510.htm ] of the Sun poised above the Earth's limb. The glare illuminates Endeavor's vertical tail (pointing toward the Earth) along with radar equipment [ http://southport.jpl.nasa.gov/ ] in the payload bay. |
|
The Planetary Nebula Show
| Title |
The Planetary Nebula Show |
| Explanation |
What do the Owl, the Cat's Eye, the Ghost of Jupiter, and Saturn have in common? They're all planetary nebulae [ http://ad.usno.navy.mil/pne/ ] of course, glowing gaseous shrouds shed by dying sun-like stars as they run out [ http://www.astro.washington.edu/balick/WFPC2/index.html ] of nuclear fuel. Beautiful to look at [ http://www.ucalgary.ca/~zhangc/pnimage.html ], the symmetric, planet-like shapes [ http://www.seds.org/messier/planetar.html ] of these cosmic clouds [ http://www.ipac.caltech.edu/2mass/gallery/ images_pne.html ], typically 1,000 times the size of our solar system [ http://www.cismall.com/deepsky/nebulae.html ], evoke their popular names. Flipping through [ http://www.noao.edu/outreach/aop/observers/ pn.html ] digital pictures made by participants in the Kitt Peak National Observatory Visitor Center's Advanced Observing Program [ http://www.noao.edu/outreach/aop/ ], astronomer Adam Block created [ http://antwrp.gsfc.nasa.gov/apod/ap010427.html ] this delightful animation. Ten different planetary nebula images are presented, each registered on the central star. In order, their catalog designations are NGC 1535 [ http://www.noao.edu/outreach/aop/observers/n1535.html ], NGC 3242 [ http://antwrp.gsfc.nasa.gov/apod/ap970331.html ] (Ghost of Jupiter), NGC 6543 [ http://home.achilles.net/~jtalbot/spectra/ Nebulium.html ] (Cat's Eye), NGC 7009 [ http://antwrp.gsfc.nasa.gov/apod/ap971230.html ] (Saturn Nebula), NGC 2438 [ http://antwrp.gsfc.nasa.gov/apod/ap990305.html ], NGC 6772 [ http://www.noao.edu/outreach/aop/observers/n6772.html ], Abell 39 [ http://antwrp.gsfc.nasa.gov/apod/ap010123.html ], NGC 7139 [ http://www.noao.edu/outreach/aop/observers/n7139.html ], NGC 6781 [ http://www.noao.edu/outreach/aop/observers/n6781.html ], and M97 [ http://www.noao.edu/outreach/aop/observers/ m97.html ] (Owl Nebula). This glorious final phase [ http://oposite.stsci.edu/pubinfo/PR/97/38/ astrofile1.html ] in the life of a star lasts only about 10,000 years. |
|
Halo of the Cat's Eye
| Title |
Halo of the Cat's Eye |
| Explanation |
The Cat's Eye Nebula [ http://antwrp.gsfc.nasa.gov/apod/ap020324.html ] (NGC 6543) is one of the best known planetary nebulae in the sky [ http://antwrp.gsfc.nasa.gov/apod/ap011003.html ]. Its haunting symmetries [ http://www.cybercom.net/~klb/ tiger.html ] are seen in the very central region of this stunning false-color picture, processed to reveal the enormous but extremely faint halo of gaseous material, over three light-years across, which surrounds the brighter, familiar planetary nebula. Made with data from the Nordic Optical Telescope [ http://www.not.iac.es/ ] in the Canary Islands, the composite picture shows emission from nitrogen atoms as red and oxygen atoms as green and blue shades. Planetary nebulae [ http://www.noao.edu/jacoby/pn_gallery.html ] have long been appreciated as a final phase in the life [ http://imagine.gsfc.nasa.gov/docs/teachers/lifecycles/ stars.html ] of a sun-like star. Only much more recently however, have some planetaries been found to have halos [ http://www.ing.iac.es/~rcorradi/HALOES/ ] like this one, likely formed of material shrugged off during earlier active episodes in the star's evolution. While the planetary nebula phase [ http://www.astro.washington.edu/balick/WFPC2/ ] is thought to last for around 10,000 years, astronomers estimate the age of the outer filamentary portions of this halo to be 50,000 to 90,000 years. |
|
M2-9: Wings of a Butterfly N
…
| Title |
M2-9: Wings of a Butterfly Nebula |
| Explanation |
Are stars better appreciated for their art after they die? Actually, stars usually create their most artistic displays "as" they die. In the case of low-mass stars like our Sun [ http://www.nineplanets.org/sol.html ] and M2-9 pictured above [ http://oposite.stsci.edu/pubinfo/PR/97/38/a.html ], the stars transform themselves from normal stars to white dwarfs [ http://antwrp.gsfc.nasa.gov/apod/ap000910.html ] by casting off their outer gaseous envelopes. The expended gas frequently forms an impressive display called a planetary nebula [ http://www.seds.org/messier/planetar.html ] that fades gradually over thousand of years. M2-9 [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1997A%26A...319..267S ], a butterfly planetary nebula [ http://antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html ] 2100 light-years [ http://chandra.harvard.edu/photo/cosmic_distance.html ] away shown in representative colors, has wings that tell a strange but incomplete tale [ http://oposite.stsci.edu/pubinfo/PR/97/38/pr.html ]. In the center, two stars [ http://antwrp.gsfc.nasa.gov/apod/ap970219.html ] orbit inside a gaseous disk 10 times the orbit of Pluto [ http://antwrp.gsfc.nasa.gov/apod/ap010319.html ]. The expelled envelope of the dying star breaks out from the disk creating the bipolar appearance [ http://antwrp.gsfc.nasa.gov/apod/ap991012.html ]. Much remains unknown about the physical processes that cause planetary nebulae [ http://www.noao.edu/jacoby/pn_gallery.html ]. |
|
Rafting for Solar Neutrinos
| Title |
Rafting for Solar Neutrinos |
| Explanation |
Where have all the neutrinos [ http://www.conknet.com/krsd/krhs/neutrino.html ] gone? A long time passing since this question was first asked (decades) as increasingly larger and more diverse detectors [ http://www.autodynamics.org/Neutrino/NeutDetc.html ] sensitive to neutrinos from our Sun [ http://www.maths.qmw.ac.uk/~lms/research/neutrino.html ] have found fewer than expected. But why? [ http://www.sns.ias.edu/~jnb/Papers/Popular/NewScientist/paper.ps ] Above, scientists check the equipment surrounding a huge tank of extremely pure water [ http://geb.phys.washington.edu/local_web/SuperK/us_prop/subsubsection3_12_3_8.html#SECTION00012380000000000000 ] from the Super-Kamiokande [ http://geb.phys.washington.edu/local_web/SuperK/us_prop/section3_12.html ] experiment in Japan, designed to detect colliding neutrinos [ http://pdg.lbl.gov/cpep/neutrinos.html ]. Large detectors are needed because the neutrino [ http://astro.caltech.edu/~bbb/paper/neutrinos.html ] is an elementary particle [ http://pdg.lbl.gov/cpep/adventure.html ] that goes right through practically everything. Reasons for the lack of solar neutrinos [ http://www.sns.ias.edu/~jnb/SNviewgraphs/snviewgraphs.html ] may include a more complex theory for electroweak interactions [ http://pdg.lbl.gov/cpep/electroweak.html ] than currently in use. Future results from detectors [ http://dept.physics.upenn.edu/~www/neutrino/solar.html ] like Super-Kamiokande may help us know more. |
|
NGC 6826: The Blinking Eye
| Title |
NGC 6826: The Blinking Eye |
| Explanation |
The colorful planetary nebula phase [ http://www.astro.washington.edu/balick/WFPC2/ ] of a sun-like star's life is brief [ http://oposite.stsci.edu/pubinfo/PR/97/38/astrofile1.html ]. Almost in the "blink of an eye" - cosmically speaking - the star's outer layers are cast off, forming an expanding emission nebula. This nebula lasts perhaps 10 thousand years compared to a 10 billion year stellar life span. Spectacular planetary nebulae [ http://oposite.stsci.edu/pubinfo/PR/97/38.html ] are familiar objects to both professional and amateur astronomers, but they still contain a few surprises. For instance, the lovely nebula NGC 6826 [ http://www.astro.washington.edu/balick/WFPC2/n6826.caption.html ], also known as the Blinking Eye Nebula, has mysterious red FLIERS [ http://antwrp.gsfc.nasa.gov/apod/ap961122.html ] seen on either side of the Hubble Space Telescope image above. Are they also expanding outward from the central star? If so, their "bow shocks" [ http://antwrp.gsfc.nasa.gov/apod/ap971203.html ] point in the wrong direction! |
|
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, 21st 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/ap980518.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/ap040111.html ] of nuclear fuel in its core. The nebula forms as the star's outer layers are expelled into space. The visible glow is generated as atoms are 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 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://www.hawastsoc.org/deepsky/vul/index.html ]. This gorgeous synthetic color picture of M27 [ http://www.eso.org/outreach/press-rel/pr-1998/ phot-38-98.html ] was produced during testing of one of the European Southern Observatory's Very Large Telescopes [ http://www.eso.org/outreach/gallery/vlt/images/Top20/ ]. |
|
The Hubble 5 Planetary Nebul
…
| Title |
The Hubble 5 Planetary Nebula |
| Explanation |
The Hubble Double Bubble Planetary Nebula is bubbling over with excitement. More mundanely known as Hubble 5 [ http://www.astro.washington.edu/balick/WFPC2/hb5.caption.html ], this bipolar planetary nebula [ http://antwrp.gsfc.nasa.gov/apod/ap971223.html ] is being created by a hot wind [ http://antwrp.gsfc.nasa.gov/apod/ap970217.html ] of particles streaming away from the central star system. The hot gas expands into the surrounding interstellar medium [ http://pegasus.phast.umass.edu/a100/handouts/ism.html ] in a fashion similar to the inflation of hot air balloons [ http://www-vrl.umich.edu/People/saha/photos.html ]. A supersonic shock-wave [ http://inuit.phys.ualberta.ca/~trpk/phys100/waves/waves.html ] can form at the boundary, causing newly excited gas there to shine as electrons [ http://pburton.maps.susx.ac.uk/scoap/physwrld/physwrld.htm ] recombine with resident elements [ http://CST.lanl.gov/CST/imagemap/periodic/periodic.html ]. In the above picture [ http://www.astro.washington.edu/balick/WFPC2/ ], colors are assigned according to the energy of the recombinant radiation. This star system lies about 2200 light-years from Earth [ http://antwrp.gsfc.nasa.gov/apod/ap970717.html ], and likely includes a Sun-like star slowly transforming itself into a white dwarf [ http://antwrp.gsfc.nasa.gov/apod/ap971102.html ]. |
|
Cat's Eye
| Title |
Cat's Eye |
| Explanation |
Staring across interstellar space, the alluring Cat's Eye [ http://heritage.stsci.edu/2004/27/ ] nebula lies three thousand light-years from Earth. A classic planetary nebula [ http://www.seds.org/messier/planetar.html ], the Cat's Eye (NGC 6543) represents a final, brief yet glorious phase [ http://www.astro.washington.edu/balick/WFPC2/ ] in the life of a sun-like star. This nebula's dying central star may have produced the simple, outer pattern of dusty concentric shells [ http://arxiv.org/abs/astro-ph/0401056 ] by shrugging [ http://antwrp.gsfc.nasa.gov/apod/ap011003.html ] off outer layers in a series of regular convulsions. But the formation of the beautiful, more complex inner structures is not well understood [ http://antwrp.gsfc.nasa.gov/apod/ap010111.html ]. Seen so clearly in this sharp Hubble [ http://hubblesite.org/newscenter/newsdesk/archive/ releases/2004/27/fastfacts/ ] Space Telescope image, the truly cosmic eye is over half a light-year across. Of course, gazing into the Cat's Eye [ http://antwrp.gsfc.nasa.gov/apod/ap031101.html ], astronomers may well be seeing the fate of our sun, destined to enter its own planetary nebula phase [ http://chandra.harvard.edu/xray_sources/ white_dwarfs.html ] of evolution ... in about 5 billion years [ http://hubblesite.org/newscenter/newsdesk/archive/ releases/1997/38/astrofile/ ]. |
|
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/ap980518.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/ap980426.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://www.astro.wisc.edu/~dolan/constellations/ constellations/Vulpecula.html ]. This gorgeous synthetic color picture of M27 [ http://www.eso.org/outreach/press-rel/pr-1998/phot-38-98.html ] was produced during testing of the European Southern Observatory's new Very Large Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap960901.html ]. |
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Albert Einstein's Miraculous
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| Title |
Albert Einstein's Miraculous Year |
| Explanation |
In 1905 Albert Einstein had [ http://www.aip.org/history/einstein/index.html ] a miraculous year [ http://www.aip.org/history/einstein/chron-1905.htm ]. One hundred [ http://msnbc.msn.com/id/7327050/ ] years ago, he wrote four papers which revolutionized our understanding of the Universe. The papers outlined, the idea that light could [ http://www.aip.org/history/einstein/ essay-photoelectric.htm ] behave as a quantized particle (a photon), an explanation of the thermal motion [ http://www.aip.org/history/einstein/brownian.htm ] of atoms and molecules (at a time when atoms themselves were just theories), a theory reconciling motion [ http://www.aip.org/history/einstein/ essay-einstein-relativity.htm ] and the constant speed of light (Special Relativity [ http://www.fourmilab.ch/etexts/einstein/specrel/www/ ]), and the idea of mass-energy [ http://www.fourmilab.ch/etexts/einstein/E_mc2/www/ ] equivalence (E=mc² [ http://www.aip.org/history/einstein/emc1.htm ]). Virtually every facet of our modern exploration of the Universe is touched by his now century old insights, along with his later theory of gravity and space-time [ http://whyfiles.org/052einstein/frame_drag4.html ] - General Relativity. In centennial celebration, consider this [ http://www.sungazer.net/einstein.html ] thoughtful view of a small telescope beside the Einstein Memorial [ http://www4.nas.edu/nas/nashome.nsf/ b57ef1bf2404952b852566dd00671bfd/5bafc8ca01417086852566ea005ecfb1 ] on the grounds of the National Academy of Sciences in Washington DC, USA. The marble platform at the bronze statue's feet is embedded with a map showing the positions of the planets, sun, moon and stars on the memorial's dedication date, 100 years after Einstein's birth in 1879. Albert Einstein [ http://www.aip.org/history/einstein/einlinks.htm ] died 50 years ago, on April 18, 1955. |
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