2004 December 19
Molecular Cloud Barnard 68
Credit: FORS Team, 8.2-meter VLT Antu, ESO
Where did all the stars go? What used to be considered a hole in the sky is now known to astronomers as a dark molecular cloud. Here, a high concentration of dust and molecular gas absorb practically all the visible light emitted from background stars. The eerily dark surroundings help make the interiors of molecular clouds some of the coldest and most isolated places in the universe. One of the most notable of these dark absorption nebulae is a cloud toward the constellation Ophiuchus known as Barnard 68, pictured above. That no stars are visible in the center indicates that Barnard 68 is relatively nearby, with measurements placing it about 500 light-years away and half a light-year across. It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form. It is possible to look right through the cloud in infrared light.
Molecular Cloud Barnard 68
Credit: FORS Team, 8.2-meter VLT Antu, ESO
Where did all the stars go? What used to be considered a hole in the sky is now known to astronomers as a dark molecular cloud. Here, a high concentration of dust and molecular gas absorb practically all the visible light emitted from background stars. The eerily dark surroundings help make the interiors of molecular clouds some of the coldest and most isolated places in the universe. One of the most notable of these dark absorption nebulae is a cloud toward the constellation Ophiuchus known as Barnard 68, pictured above. That no stars are visible in the center indicates that Barnard 68 is relatively nearby, with measurements placing it about 500 light-years away and half a light-year across. It is not known exactly how molecular clouds like Barnard 68 form, but it is known that these clouds are themselves likely places for new stars to form. It is possible to look right through the cloud in infrared light.
2004 December 20
Titan Surmised
Illustration Credit & Copyright: Craig Attebery, ESA, NASA
What does the surface of Titan look like? Thick clouds have always made Saturn's largest moon so mysterious that seemingly farfetched hypotheses like methane rain and lakes have been seriously considered. Later this week, the Cassini spacecraft orbiting Saturn is scheduled to release its probe named Huygens that will actually attempt to land on the shrouded moon in early January. Sketched above is one educated guess of what Huygens might find. In the above depiction, orange hydrocarbons color a landscape covered with lakes and peaks of frozen methane and ammonia. For illustration purposes, the Huygens probe is drawn parachuting down with an oversized Cassini spacecraft orbiting above. Saturn, likely occluded by the clouds, is depicted looming in the distance. What will Huygens really find? Are the building blocks of life frozen onto the surface of Titan? Will the truth be stranger than we imagined?
Titan Surmised
Illustration Credit & Copyright: Craig Attebery, ESA, NASA
What does the surface of Titan look like? Thick clouds have always made Saturn's largest moon so mysterious that seemingly farfetched hypotheses like methane rain and lakes have been seriously considered. Later this week, the Cassini spacecraft orbiting Saturn is scheduled to release its probe named Huygens that will actually attempt to land on the shrouded moon in early January. Sketched above is one educated guess of what Huygens might find. In the above depiction, orange hydrocarbons color a landscape covered with lakes and peaks of frozen methane and ammonia. For illustration purposes, the Huygens probe is drawn parachuting down with an oversized Cassini spacecraft orbiting above. Saturn, likely occluded by the clouds, is depicted looming in the distance. What will Huygens really find? Are the building blocks of life frozen onto the surface of Titan? Will the truth be stranger than we imagined?
2004 December 21
Titan Disguised
Illustration Credit & Copyright: Mark Garlick (Space-art)
Will the Huygens probe land or splash down? In the next few days, the Cassini spacecraft currently orbiting Saturn will release a probe that will descend toward Saturn's largest moon in mid-January. That moon, Titan, has a surface normally hidden from view by thick methane cloud decks. What the car-sized flying-saucer-shaped probe will find is unknown. Once reaching the surface, Huygens may survive for as long as 150 minutes and take as many as 1,100 images. These images will be beamed up to the passing Cassini mothership for subsequent transmission to a waiting Earth. The Huygens probe is depicted above entering Titan's atmosphere and deploying its parachute. Uncovering the most mysterious moon in the Solar System may reveal a surface so strange that images of it may not be immediately understood.
Titan Disguised
Illustration Credit & Copyright: Mark Garlick (Space-art)
Will the Huygens probe land or splash down? In the next few days, the Cassini spacecraft currently orbiting Saturn will release a probe that will descend toward Saturn's largest moon in mid-January. That moon, Titan, has a surface normally hidden from view by thick methane cloud decks. What the car-sized flying-saucer-shaped probe will find is unknown. Once reaching the surface, Huygens may survive for as long as 150 minutes and take as many as 1,100 images. These images will be beamed up to the passing Cassini mothership for subsequent transmission to a waiting Earth. The Huygens probe is depicted above entering Titan's atmosphere and deploying its parachute. Uncovering the most mysterious moon in the Solar System may reveal a surface so strange that images of it may not be immediately understood.
2004 December 22
Comet, Meteor, Nebula, Star
Credit & Copyright: Wally Pacholka (Astropics)
Several wonders of the late-year northern sky appeared together for a few fleeting moments on December 13. On the bottom left, just above the hill, is blue Sirius, the brightest star in the sky. Above Sirius and slightly to the right of the belt of Orion is the red Orion Nebula, one of the most famous nebulas on the sky. Below and to the right of the Orion Nebula streaks a yellow meteor, although moving in the wrong direction to be from the Geminids meteor shower that peaked the night. Finally, above and to the right of the meteor is Comet Machholz, whose coma appears here relatively green. Since the time since this image was taken over a Californian hill, the Geminid meteor has long since evaporated. Comet Machholz has brightened and moved to the north. Sirius, however, will remain in the constellation of Canis Major indefinitely.
Comet, Meteor, Nebula, Star
Credit & Copyright: Wally Pacholka (Astropics)
Several wonders of the late-year northern sky appeared together for a few fleeting moments on December 13. On the bottom left, just above the hill, is blue Sirius, the brightest star in the sky. Above Sirius and slightly to the right of the belt of Orion is the red Orion Nebula, one of the most famous nebulas on the sky. Below and to the right of the Orion Nebula streaks a yellow meteor, although moving in the wrong direction to be from the Geminids meteor shower that peaked the night. Finally, above and to the right of the meteor is Comet Machholz, whose coma appears here relatively green. Since the time since this image was taken over a Californian hill, the Geminid meteor has long since evaporated. Comet Machholz has brightened and moved to the north. Sirius, however, will remain in the constellation of Canis Major indefinitely.
2004 December 23
3C58: Pulsar Power
Credit: P. Slane (Harvard-Smithsonian CfA) et al., CXC, NASA
Light from a star that exploded some ten thousand light-years away first reached our fair planet in the year 1181. Now known as supernova remnant 3C58, the region seen in this false-color image glows in x-rays, powered by a rapidly spinning neutron star or pulsar - the dense remains of the collapsed stellar core. A cosmic dynamo with more mass than the sun, the pulsar's electromagnetic fields seem to accelerate particles to enormous energies, creating the jets, rings, and loop structures visible in this stunning x-ray view from the orbiting Chandra Observatory. While adding 3C58 to the list of pulsar powered nebulae explored with Chandra, astronomers have deduced that the pulsar itself is much too cool for its tender years, citing 3C58 as a show case of extreme physics not well understood. The close-up inset above spans about six light-years.
3C58: Pulsar Power
Credit: P. Slane (Harvard-Smithsonian CfA) et al., CXC, NASA
Light from a star that exploded some ten thousand light-years away first reached our fair planet in the year 1181. Now known as supernova remnant 3C58, the region seen in this false-color image glows in x-rays, powered by a rapidly spinning neutron star or pulsar - the dense remains of the collapsed stellar core. A cosmic dynamo with more mass than the sun, the pulsar's electromagnetic fields seem to accelerate particles to enormous energies, creating the jets, rings, and loop structures visible in this stunning x-ray view from the orbiting Chandra Observatory. While adding 3C58 to the list of pulsar powered nebulae explored with Chandra, astronomers have deduced that the pulsar itself is much too cool for its tender years, citing 3C58 as a show case of extreme physics not well understood. The close-up inset above spans about six light-years.
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2004 December 24
Swift RocketCam
Credit: Dan Maas (Maas Digital), Ecliptic Enterprises Corporation, NASA
A forward-facing RocketCam (TM) mounted inside the payload fairing of a Delta II rocket captured these dramatic video frames on November 20th -- as the Swift satellite observatory journeyed to an orbit 600 kilometers above planet Earth. Some frames were interpolated to correct for transmission problems. The sequence shows the fairing separation, the second stage rotating past the Earth's limb, and finally the 1500 kilogram satellite itself separating from the second stage. Observing at optical, ultraviolet, x-ray and gamma-ray energies, Swift is designed to locate the sources of energetic gamma-ray bursts and watch as their afterglows fade in the distant Universe. Still in its checkout phase, the observatory is already detecting the high energy flashes from these awe-inspiring cosmic blasts.
Swift RocketCam
Credit: Dan Maas (Maas Digital), Ecliptic Enterprises Corporation, NASA
A forward-facing RocketCam (TM) mounted inside the payload fairing of a Delta II rocket captured these dramatic video frames on November 20th -- as the Swift satellite observatory journeyed to an orbit 600 kilometers above planet Earth. Some frames were interpolated to correct for transmission problems. The sequence shows the fairing separation, the second stage rotating past the Earth's limb, and finally the 1500 kilogram satellite itself separating from the second stage. Observing at optical, ultraviolet, x-ray and gamma-ray energies, Swift is designed to locate the sources of energetic gamma-ray bursts and watch as their afterglows fade in the distant Universe. Still in its checkout phase, the observatory is already detecting the high energy flashes from these awe-inspiring cosmic blasts.
2004 December 25
Big Beautiful Saturn
Composition Credit: Mattias Malmer, Image Data: Cassini Imaging Team
As a present to APOD readers, digital imager Mattias Malmer offers a very high resolution view of big beautiful Saturn. A labor of love, his full mosaic, composite image is contained in a large 5 megabyte jpeg file (preview here, download here) and spans the gorgeous gas giant from ring tip to ring tip. It was pieced together from 102 frames (N00020905 to N00021033) recorded by the Cassini spacecraft ISS on October 6, 2004. The red, green, and blue frames are all uncalibrated, unvalidated images available to the public through the Cassini web site. Malmer's full panorama has a pixel size of 8400 by 3300, so only a substantially cropped version appears above. Enjoy the view and have a safe and Happy Holiday Season!
Big Beautiful Saturn
Composition Credit: Mattias Malmer, Image Data: Cassini Imaging Team
As a present to APOD readers, digital imager Mattias Malmer offers a very high resolution view of big beautiful Saturn. A labor of love, his full mosaic, composite image is contained in a large 5 megabyte jpeg file (preview here, download here) and spans the gorgeous gas giant from ring tip to ring tip. It was pieced together from 102 frames (N00020905 to N00021033) recorded by the Cassini spacecraft ISS on October 6, 2004. The red, green, and blue frames are all uncalibrated, unvalidated images available to the public through the Cassini web site. Malmer's full panorama has a pixel size of 8400 by 3300, so only a substantially cropped version appears above. Enjoy the view and have a safe and Happy Holiday Season!
2004 December 26
GRO J1655-40: Evidence for a Spinning Black Hole
Drawing Credit: A. Hobart, CXC
In the center of a swirling whirlpool of hot gas is likely a beast that has never been seen directly: a black hole. Studies of the bright light emitted by the swirling gas frequently indicate not only that a black hole is present, but also likely attributes. The gas surrounding GRO J1655-40, for example, has been found to display an unusual flickering at a rate of 450 times a second. Given a previous mass estimate for the central object of seven times the mass of our Sun, the rate of the fast flickering can be explained by a black hole that is rotating very rapidly. What physical mechanisms actually cause the flickering -- and a slower quasi-periodic oscillation (QPO) -- in accretion disks surrounding black holes and neutron stars remains a topic of much research.
GRO J1655-40: Evidence for a Spinning Black Hole
Drawing Credit: A. Hobart, CXC
In the center of a swirling whirlpool of hot gas is likely a beast that has never been seen directly: a black hole. Studies of the bright light emitted by the swirling gas frequently indicate not only that a black hole is present, but also likely attributes. The gas surrounding GRO J1655-40, for example, has been found to display an unusual flickering at a rate of 450 times a second. Given a previous mass estimate for the central object of seven times the mass of our Sun, the rate of the fast flickering can be explained by a black hole that is rotating very rapidly. What physical mechanisms actually cause the flickering -- and a slower quasi-periodic oscillation (QPO) -- in accretion disks surrounding black holes and neutron stars remains a topic of much research.
2004 December 27
Andromeda's Core
Credit & Copyright: Robert Gendler
The center of the Andromeda galaxy is beautiful but strange. Andromeda, indexed as M31, is so close to our own Milky Way Galaxy that it gives a unique perspective into galaxy composition by allowing us to see into its core. Billions of stars swarm around a center that has two nuclei and likely houses a supermassive black hole over 5 million times the mass of our Sun. M31 is about two million light years away and visible with the unaided eye towards the constellation of Andromeda, the princess. Pictured above, dark knots of dust are seen superposed on the inner 10,000 light years of M31's core. The brighter stars are foreground stars located in our Milky Way Galaxy.
Andromeda's Core
Credit & Copyright: Robert Gendler
The center of the Andromeda galaxy is beautiful but strange. Andromeda, indexed as M31, is so close to our own Milky Way Galaxy that it gives a unique perspective into galaxy composition by allowing us to see into its core. Billions of stars swarm around a center that has two nuclei and likely houses a supermassive black hole over 5 million times the mass of our Sun. M31 is about two million light years away and visible with the unaided eye towards the constellation of Andromeda, the princess. Pictured above, dark knots of dust are seen superposed on the inner 10,000 light years of M31's core. The brighter stars are foreground stars located in our Milky Way Galaxy.
2004 December 28
Tentacles of the Tarantula Nebula
Credit & Copyright: WFI, MPG/ESO 2.2-m Telescope, La Silla, ESO
The Tarantula Nebula is a giant emission nebula within our neighboring galaxy the Large Magellanic Cloud. Inside this cosmic arachnid lies a huge central young cluster of massive stars, cataloged as R136 and partially visible on the upper right. The energetic light and winds from this cluster light up the nebula and sculpt the surrounding gas and dust into vast complex filaments. These "tentacles" give the Tarantula Nebula its name. In this impressive color image from the Wide-Field Imager camera on ESO's 2.2-meter telescope at La Silla Observatory, intricacies of the nebula's complex array of dust and gas are visible. A 300 light-year portion of the Tarantula Nebula is imaged. The Tarantula Nebula, also dubbed 30 Doradus, lies 170,000 light years away toward the constellation of Dorado.
Tentacles of the Tarantula Nebula
Credit & Copyright: WFI, MPG/ESO 2.2-m Telescope, La Silla, ESO
The Tarantula Nebula is a giant emission nebula within our neighboring galaxy the Large Magellanic Cloud. Inside this cosmic arachnid lies a huge central young cluster of massive stars, cataloged as R136 and partially visible on the upper right. The energetic light and winds from this cluster light up the nebula and sculpt the surrounding gas and dust into vast complex filaments. These "tentacles" give the Tarantula Nebula its name. In this impressive color image from the Wide-Field Imager camera on ESO's 2.2-meter telescope at La Silla Observatory, intricacies of the nebula's complex array of dust and gas are visible. A 300 light-year portion of the Tarantula Nebula is imaged. The Tarantula Nebula, also dubbed 30 Doradus, lies 170,000 light years away toward the constellation of Dorado.
2004 December 29
The Helix Nebula from Blanco and Hubble
Credit: C. R. O'Dell, (Vanderbilt) et al. ESA, NASA
How did a star create the Helix nebula? The shapes of planetary nebula like the Helix are important because they likely hold clues to how stars like the Sun end their lives. Recent observations by the orbiting Hubble Space Telescope and the 4-meter Blanco Telescope in Chile, however, have shown the Helix is not really a simple helix. Rather, it incorporates two nearly perpendicular disks as well as arcs, shocks, and even features not well understood. Even so, many strikingly geometric symmetries remain. How a single Sun-like star created such beautiful yet geometric complexity is a topic of research. The Helix Nebula is the nearest planetary nebula to Earth, lies only about 700 light years away toward the constellation of Aquarius, and spans about 3 light-years.
The Helix Nebula from Blanco and Hubble
Credit: C. R. O'Dell, (Vanderbilt) et al. ESA, NASA
How did a star create the Helix nebula? The shapes of planetary nebula like the Helix are important because they likely hold clues to how stars like the Sun end their lives. Recent observations by the orbiting Hubble Space Telescope and the 4-meter Blanco Telescope in Chile, however, have shown the Helix is not really a simple helix. Rather, it incorporates two nearly perpendicular disks as well as arcs, shocks, and even features not well understood. Even so, many strikingly geometric symmetries remain. How a single Sun-like star created such beautiful yet geometric complexity is a topic of research. The Helix Nebula is the nearest planetary nebula to Earth, lies only about 700 light years away toward the constellation of Aquarius, and spans about 3 light-years.
2004 December 30
M81 and M82: GALEX Full Field
Credit: GALEX Team, Caltech, NASA
Intriguing galaxy pair M81 and M82 shine in this full-field view from the orbiting GALEX observatory. GALEX - the Galaxy Evolution Explorer - scans the cosmos in ultraviolet light, a view that follows star formation and galaxy evolution through the Universe. Near the bottom, magnificent spiral galaxy M81, similar in size to our own Milky Way, shows off young stars in winding spiral arms. Less than 100 million years old, the young stars are blue in the false-color GALEX image and seen to be well separated from the older yellowish stars of the galactic core. But near the top, turbulent, irregular galaxy M82 shows the results of extreme rates of star birth and death. Supernovae, the death explosions of massive stars, contribute to a violent wind of material expelled from M82's central regions. The striking irregular and spiral galaxy pair are located only about 10 million light-years away in the northern constellation Ursa Major.
M81 and M82: GALEX Full Field
Credit: GALEX Team, Caltech, NASA
Intriguing galaxy pair M81 and M82 shine in this full-field view from the orbiting GALEX observatory. GALEX - the Galaxy Evolution Explorer - scans the cosmos in ultraviolet light, a view that follows star formation and galaxy evolution through the Universe. Near the bottom, magnificent spiral galaxy M81, similar in size to our own Milky Way, shows off young stars in winding spiral arms. Less than 100 million years old, the young stars are blue in the false-color GALEX image and seen to be well separated from the older yellowish stars of the galactic core. But near the top, turbulent, irregular galaxy M82 shows the results of extreme rates of star birth and death. Supernovae, the death explosions of massive stars, contribute to a violent wind of material expelled from M82's central regions. The striking irregular and spiral galaxy pair are located only about 10 million light-years away in the northern constellation Ursa Major.
2004 December 31
A Year of Mars Roving
Credit: Mars Exploration Rover Mission, JPL, NASA
Landing on Mars in January, NASA's twin rovers Spirit and Opportunity have now each spent over 330 sols roving the martian surface. Still healthy and well in to extended missions, the golfcart sized robots have operated five times longer than planned. Ranging across the floor of Gusev crater, the Spirit rover has reached the Columbia Hills and journeyed nearly four kilometers. Half a planet away, Opportunity has spent much of its tour on Meridiani Planum exploring the 130 meter wide Endurance Crater. Opportunity recently returned this panoramic view of rock outcrops and steep crater walls. Both rovers have uncovered strong evidence that ancient salty oceans left their mark on the alluring Red Planet.
A Year of Mars Roving
Credit: Mars Exploration Rover Mission, JPL, NASA
Landing on Mars in January, NASA's twin rovers Spirit and Opportunity have now each spent over 330 sols roving the martian surface. Still healthy and well in to extended missions, the golfcart sized robots have operated five times longer than planned. Ranging across the floor of Gusev crater, the Spirit rover has reached the Columbia Hills and journeyed nearly four kilometers. Half a planet away, Opportunity has spent much of its tour on Meridiani Planum exploring the 130 meter wide Endurance Crater. Opportunity recently returned this panoramic view of rock outcrops and steep crater walls. Both rovers have uncovered strong evidence that ancient salty oceans left their mark on the alluring Red Planet.
2005 January 1
Manicouagan Impact Crater
Credit: STS-9 Crew, NASA
Manicouagan Crater in northern Canada is one of the oldest impact craters known. Formed about 200 million years ago, the present day terrain supports a 70-kilometer diameter hydroelectric reservoir in the telltale form of an annular lake. The crater itself has been worn away by the passing of glaciers and other erosional processes. Still, the hard rock at the impact site has preserved much of the complex impact structure and so allows scientists a leading case to help understand large impact features on Earth and other Solar System bodies. Also visible above is the vertical fin of the Space Shuttle Columbia from which the picture was taken in 1983.
Manicouagan Impact Crater
Credit: STS-9 Crew, NASA
Manicouagan Crater in northern Canada is one of the oldest impact craters known. Formed about 200 million years ago, the present day terrain supports a 70-kilometer diameter hydroelectric reservoir in the telltale form of an annular lake. The crater itself has been worn away by the passing of glaciers and other erosional processes. Still, the hard rock at the impact site has preserved much of the complex impact structure and so allows scientists a leading case to help understand large impact features on Earth and other Solar System bodies. Also visible above is the vertical fin of the Space Shuttle Columbia from which the picture was taken in 1983.
2005 January 2
Welcome to Planet Earth
Credit: Apollo 17 Crew, NASA
Welcome to Planet Earth, the third planet from a star named the Sun. The Earth is shaped like a sphere and composed mostly of rock. Over 70 percent of the Earth's surface is water. The planet has a relatively thin atmosphere composed mostly of nitrogen and oxygen. Earth has a single large Moon that is about 1/4 of its diameter and, from the planet's surface, is seen to have almost exactly the same angular size as the Sun. With its abundance of liquid water, Earth supports a large variety of life forms, including potentially intelligent species such as dolphins and humans. Please enjoy your stay on Planet Earth.
Welcome to Planet Earth
Credit: Apollo 17 Crew, NASA
Welcome to Planet Earth, the third planet from a star named the Sun. The Earth is shaped like a sphere and composed mostly of rock. Over 70 percent of the Earth's surface is water. The planet has a relatively thin atmosphere composed mostly of nitrogen and oxygen. Earth has a single large Moon that is about 1/4 of its diameter and, from the planet's surface, is seen to have almost exactly the same angular size as the Sun. With its abundance of liquid water, Earth supports a large variety of life forms, including potentially intelligent species such as dolphins and humans. Please enjoy your stay on Planet Earth.
2005 January 3
The Pleiades Star Cluster
Credit and Copyright: Matthew T. Russell
Perhaps the most famous star cluster on the sky, the Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the brighter cluster stars. Low mass, faint, brown dwarfs have also been found in the Pleiades. (Editors' note: The prominent diffraction spikes are caused by the telescope itself and may be either distracting or provide aesthetic enhancement, depending on your point of view.)
The Pleiades Star Cluster
Credit and Copyright: Matthew T. Russell
Perhaps the most famous star cluster on the sky, the Pleiades can be seen without binoculars from even the depths of a light-polluted city. Also known as the Seven Sisters and M45, the Pleiades is one of the brightest and closest open clusters. The Pleiades contains over 3000 stars, is about 400 light years away, and only 13 light years across. Quite evident in the above photograph are the blue reflection nebulae that surround the brighter cluster stars. Low mass, faint, brown dwarfs have also been found in the Pleiades. (Editors' note: The prominent diffraction spikes are caused by the telescope itself and may be either distracting or provide aesthetic enhancement, depending on your point of view.)
2005 January 4
Milky Way Illustrated
Illustration Credit & Copyright: Mark Garlick (Space-art)
What does our Milky Way Galaxy look like from afar? Since we are stuck inside, and since opaque dust truncates our view in visible light, nobody knows for sure. Drawn above, however, is a good guess based on many different types of observations. In the Milky Way's center is a very bright core region centered on a large black hole. The Milky Way's bright central bulge is now thought to be an asymmetrical bar of relatively old and red stars. The outer regions are where the spiral arms are found, dominated in appearance by open clusters of young, bright, blue stars, by red emission nebula, and by dark dust. The spiral arms reside in a disk dominated in mass by relatively dim stars and loose gas composed mostly of hydrogen. What is not depicted is a huge spherical halo of invisible dark matter that dominates the mass of the Milky Way as well as the motions of stars away from the center.
Milky Way Illustrated
Illustration Credit & Copyright: Mark Garlick (Space-art)
What does our Milky Way Galaxy look like from afar? Since we are stuck inside, and since opaque dust truncates our view in visible light, nobody knows for sure. Drawn above, however, is a good guess based on many different types of observations. In the Milky Way's center is a very bright core region centered on a large black hole. The Milky Way's bright central bulge is now thought to be an asymmetrical bar of relatively old and red stars. The outer regions are where the spiral arms are found, dominated in appearance by open clusters of young, bright, blue stars, by red emission nebula, and by dark dust. The spiral arms reside in a disk dominated in mass by relatively dim stars and loose gas composed mostly of hydrogen. What is not depicted is a huge spherical halo of invisible dark matter that dominates the mass of the Milky Way as well as the motions of stars away from the center.
2005 January 5
Comet Machholz in View
Credit & Copyright: Jimmy Westlake (Colorado Mountain College)
Good views of Comet Machholz are in store for northern hemisphere comet watchers in January. Now making its closest approach to planet Earth, the comet will pass near the lovely Pleiades star cluster on January 7th and the double star cluster in Perseus on January 27th as Machholz moves relatively quickly through the evening sky. Currently just visible to the unaided eye from dark locations, the comet should be an easy target in binoculars or a small telescope. In fact, this telephoto time exposure from January 1 shows Comet Machholz sporting two lovely tails in skies over Colorado, USA. Extending to the left, strands of the comet's ion or gas tail are readily affected by the solar breeze and point away from the Sun. Dust, which tends to trail along the comet's orbit, forms the tail jutting down and to the right.
Comet Machholz in View
Credit & Copyright: Jimmy Westlake (Colorado Mountain College)
Good views of Comet Machholz are in store for northern hemisphere comet watchers in January. Now making its closest approach to planet Earth, the comet will pass near the lovely Pleiades star cluster on January 7th and the double star cluster in Perseus on January 27th as Machholz moves relatively quickly through the evening sky. Currently just visible to the unaided eye from dark locations, the comet should be an easy target in binoculars or a small telescope. In fact, this telephoto time exposure from January 1 shows Comet Machholz sporting two lovely tails in skies over Colorado, USA. Extending to the left, strands of the comet's ion or gas tail are readily affected by the solar breeze and point away from the Sun. Dust, which tends to trail along the comet's orbit, forms the tail jutting down and to the right.
2005 January 6
UKIRT: Aloha Orion
Credit: Joint Astronomy Centre; image processing by C. Davis, W. Varricatt
At the edge of a dense molecular cloud, filaments of gas, cosmic dust, and a multitude of young stars beckon in this penetrating image of the Orion Nebula. Alluring structures in the well-known star forming region are revealed here in infrared light as viewed by a new Hawaiian eye - WFCAM - a powerful wide field camera commissioned at the United Kingdom Infrared Telescope (UKIRT) on Mauna Kea. Only a fraction of WFCAM's full field, this picture covers about 11 light-years at the 1,500 light-year distance of the nebula. In the image, otherwise invisible infrared light has been mapped into visible colors. Red represents narrow-band infrared emission from hydrogen molecules at a wavelength of 2.12 microns, green is emission at 2.2 microns, and blue is emission at 1.25 microns. Visible light has a wavelength of about 0.5 microns (micrometers).
UKIRT: Aloha Orion
Credit: Joint Astronomy Centre; image processing by C. Davis, W. Varricatt
At the edge of a dense molecular cloud, filaments of gas, cosmic dust, and a multitude of young stars beckon in this penetrating image of the Orion Nebula. Alluring structures in the well-known star forming region are revealed here in infrared light as viewed by a new Hawaiian eye - WFCAM - a powerful wide field camera commissioned at the United Kingdom Infrared Telescope (UKIRT) on Mauna Kea. Only a fraction of WFCAM's full field, this picture covers about 11 light-years at the 1,500 light-year distance of the nebula. In the image, otherwise invisible infrared light has been mapped into visible colors. Red represents narrow-band infrared emission from hydrogen molecules at a wavelength of 2.12 microns, green is emission at 2.2 microns, and blue is emission at 1.25 microns. Visible light has a wavelength of about 0.5 microns (micrometers).
2005 January 7
S is for Venus
Credit & Copyright: Tun� Tezel
Planet Venus traced out this S shape in Earth's sky during 2004. Following the second planet from the Sun in a series of 29 images recorded from April 3rd through August 7th (top right to bottom left) of that year, astronomer Tunc Tezel constructed this composite illustrating the wandering planet's path against the background stars. The series reveals Venus' apparent retrograde motion transporting it from a brilliant evening star to morning's celestial beacon. Of course, in 2004, after sinking into the evening twilight but before rising above the predawn horizon, Venus was seen in silhouette against the Sun (near center) - the first transit of Venus since 1882. The next time Venus will wander across the solar disk is in 2012.
S is for Venus
Credit & Copyright: Tun� Tezel
Planet Venus traced out this S shape in Earth's sky during 2004. Following the second planet from the Sun in a series of 29 images recorded from April 3rd through August 7th (top right to bottom left) of that year, astronomer Tunc Tezel constructed this composite illustrating the wandering planet's path against the background stars. The series reveals Venus' apparent retrograde motion transporting it from a brilliant evening star to morning's celestial beacon. Of course, in 2004, after sinking into the evening twilight but before rising above the predawn horizon, Venus was seen in silhouette against the Sun (near center) - the first transit of Venus since 1882. The next time Venus will wander across the solar disk is in 2012.
2005 January 8
X-Ray Mystery in RCW 38
Credit: S. Wolk (Harvard-Smithsonian CfA), et al., CXC, NASA
A mere 6,000 light-years distant and sailing through the constellation Vela, star cluster RCW 38 is full of powerful stars. It's no surprise that these stars, only a million years young with hot outer atmospheres, appear as point-like x-ray sources dotting this x-ray image from the orbiting Chandra Observatory. But the diffuse cloud of x-rays surrounding them is a bit mysterious. The image is color coded by x-ray energy, with high energies in blue, medium in green, and low energy x-rays in red. Just a few light-years across, the cloud which pervades the cluster has colors suggesting the x-rays are produced by high energy electrons moving through magnetic fields. Yet a source of energetic electrons, such as shockwaves from exploding stars (supernova remnants), or rotating neutron stars (pulsars), is not apparent in the Chandra data. Whatever their origins, the energetic particles could leave an imprint on planetary systems forming in young star cluster RCW 38, just as nearby energetic events seem to have affected the chemistry and isotopes found in our own solar system.
X-Ray Mystery in RCW 38
Credit: S. Wolk (Harvard-Smithsonian CfA), et al., CXC, NASA
A mere 6,000 light-years distant and sailing through the constellation Vela, star cluster RCW 38 is full of powerful stars. It's no surprise that these stars, only a million years young with hot outer atmospheres, appear as point-like x-ray sources dotting this x-ray image from the orbiting Chandra Observatory. But the diffuse cloud of x-rays surrounding them is a bit mysterious. The image is color coded by x-ray energy, with high energies in blue, medium in green, and low energy x-rays in red. Just a few light-years across, the cloud which pervades the cluster has colors suggesting the x-rays are produced by high energy electrons moving through magnetic fields. Yet a source of energetic electrons, such as shockwaves from exploding stars (supernova remnants), or rotating neutron stars (pulsars), is not apparent in the Chandra data. Whatever their origins, the energetic particles could leave an imprint on planetary systems forming in young star cluster RCW 38, just as nearby energetic events seem to have affected the chemistry and isotopes found in our own solar system.