1999 April 16
Upsilon Andromedae: An Extra-Solar System
Drawing Credit & Copyright: Lynette Cook
Yesterday, astronomers announced the discovery of the first system of planets around a normal star other than our Sun. Previously, only single planet star systems had been found. Subtle changes in the wobble of Upsilon Andromedae, a Sun-like star in the constellation of Andromeda, allowed astronomers led by R. Paul Butler (AAO) and Geoffrey W. Marcy (SFSU /UCB) to make the breakthrough. This star system is quite different from our own Solar System, however. All three detected planets have masses near or above Jupiter. The discovery implies that multiple-planet systems are quite common, increasing speculation that life-bearing planets similar to Earth may one day be found. The drawing above is an artist's depiction of the Upsilon Andromedae system and its innermost planet. This planet orbits unexpectedly close to its parent star.
Upsilon Andromedae: An Extra-Solar System
Drawing Credit & Copyright: Lynette Cook
Yesterday, astronomers announced the discovery of the first system of planets around a normal star other than our Sun. Previously, only single planet star systems had been found. Subtle changes in the wobble of Upsilon Andromedae, a Sun-like star in the constellation of Andromeda, allowed astronomers led by R. Paul Butler (AAO) and Geoffrey W. Marcy (SFSU /UCB) to make the breakthrough. This star system is quite different from our own Solar System, however. All three detected planets have masses near or above Jupiter. The discovery implies that multiple-planet systems are quite common, increasing speculation that life-bearing planets similar to Earth may one day be found. The drawing above is an artist's depiction of the Upsilon Andromedae system and its innermost planet. This planet orbits unexpectedly close to its parent star.
1999 April 17
Gamma Ray Moon
Credit: D. Thompson (LHEA,GSFC) et al., EGRET, Compton Observatory, NASA
What if you could see gamma rays (photons with more than 40 million times the energy of visible light)? If you could, the Moon would appear brighter than the Sun! This startling notion is demonstrated by this image of the Moon from the Energetic Gamma Ray Experiment Telescope (EGRET) onboard NASA's orbiting Compton Gamma Ray Observatory. The most sensitive instrument of its kind, even EGRET can not see the quiet Sun which is faint at extreme gamma-ray energies. Why is the Moon so bright in gamma rays? High energy charged particles known as cosmic rays, constantly bombard the unprotected lunar surface generating gamma rays. EGRET's gamma-ray vision is not sharp enough to resolve a lunar disk or any surface features but its sensitivity reveals the bright gamma-ray moonglow against a background of gamma rays from our Milky Way galaxy, gamma-ray quasars and some still mysterious unidentified sources. The image was generated from eight exposures made during 1991-1994. A wide-angle picture, it covers a roughly 40x40 degree field of view with gamma-ray intensity represented in false color.
Gamma Ray Moon
Credit: D. Thompson (LHEA,GSFC) et al., EGRET, Compton Observatory, NASA
What if you could see gamma rays (photons with more than 40 million times the energy of visible light)? If you could, the Moon would appear brighter than the Sun! This startling notion is demonstrated by this image of the Moon from the Energetic Gamma Ray Experiment Telescope (EGRET) onboard NASA's orbiting Compton Gamma Ray Observatory. The most sensitive instrument of its kind, even EGRET can not see the quiet Sun which is faint at extreme gamma-ray energies. Why is the Moon so bright in gamma rays? High energy charged particles known as cosmic rays, constantly bombard the unprotected lunar surface generating gamma rays. EGRET's gamma-ray vision is not sharp enough to resolve a lunar disk or any surface features but its sensitivity reveals the bright gamma-ray moonglow against a background of gamma rays from our Milky Way galaxy, gamma-ray quasars and some still mysterious unidentified sources. The image was generated from eight exposures made during 1991-1994. A wide-angle picture, it covers a roughly 40x40 degree field of view with gamma-ray intensity represented in false color.
1999 April 18
Moon Over California
Credit and Copyright: Joe Orman
The Moon, Saturn, and Venus shine above while city lights twinkle below in the deepening twilight of March 19. Taken from outside Indio, California, the photo shows the city lights of Indio and nearby Palm Springs. The brilliant lunar crescent is over exposed here with Saturn about 4 degrees away to the upper right and bright Venus still farther to the right only another 2 degrees or so. This Sunday evening, April 18, another dramatic lunar spectacle should be easily visible to stargazers in the western and midwestern US when the crescent moon passes in front of the bright star Aldebaran.
Moon Over California
Credit and Copyright: Joe Orman
The Moon, Saturn, and Venus shine above while city lights twinkle below in the deepening twilight of March 19. Taken from outside Indio, California, the photo shows the city lights of Indio and nearby Palm Springs. The brilliant lunar crescent is over exposed here with Saturn about 4 degrees away to the upper right and bright Venus still farther to the right only another 2 degrees or so. This Sunday evening, April 18, another dramatic lunar spectacle should be easily visible to stargazers in the western and midwestern US when the crescent moon passes in front of the bright star Aldebaran.
1999 April 19
The Full Moon
Credit: Lick Observatory
Earth has one moon. A symbol in famous love songs, movies, poems, and folklore, many myths about the Moon date back to ancient history. In fact, the name Monday originates from Moon-day. The Moon glows by light it reflects from the Sun and is frequently the brightest object in the night sky. The Moon orbits the Earth about once a month (moon-th) from about 1 light second away. The above-pictured Full Moon occurs when the Moon is nearly opposite to the Sun in its orbit. The Moon's diameter is about 1/4 that of the Earth, and from the Earth's surface appears to have almost exactly the same angular size as the Sun. Recent evidence indicates that the Moon formed from a colossal impact on the Earth about 4.5 billions of years ago, and therefore has a similar composition to the Earth. Humans walked on the Moon for the first time in 1969.
The Full Moon
Credit: Lick Observatory
Earth has one moon. A symbol in famous love songs, movies, poems, and folklore, many myths about the Moon date back to ancient history. In fact, the name Monday originates from Moon-day. The Moon glows by light it reflects from the Sun and is frequently the brightest object in the night sky. The Moon orbits the Earth about once a month (moon-th) from about 1 light second away. The above-pictured Full Moon occurs when the Moon is nearly opposite to the Sun in its orbit. The Moon's diameter is about 1/4 that of the Earth, and from the Earth's surface appears to have almost exactly the same angular size as the Sun. Recent evidence indicates that the Moon formed from a colossal impact on the Earth about 4.5 billions of years ago, and therefore has a similar composition to the Earth. Humans walked on the Moon for the first time in 1969.
1999 April 20
Candidates for a Hypernova
Credit: Y. Chu (UIUC) et al., POSS, ROSAT, MDM, HST
What created these huge explosion remnants? Speculation has been building recently that outbursts even more powerful than well-known supernovae might occur. Dubbed hypernovae, these explosions might result from high-mass stars and liberate perhaps ten times more energy than conventional supernovae. A hypernova was originally postulated to explain the great amount of energy seemingly liberated in a gamma-ray burst. A search for visible remnants of hypernovae has now yielded the above two candidates. Nearby spiral galaxy M101, shown on the right, has two large expanding shells that might have originated from a hypernova. Remnant NGC 5471B on the upper left and MF83 below were identified by the unusually high amount of X-ray radiation they emit. MF83 is also one of the largest expanding shells ever found. Research continues into the possible nature and visibility of hypernovae and the gas shells they likely leave behind.
Candidates for a Hypernova
Credit: Y. Chu (UIUC) et al., POSS, ROSAT, MDM, HST
What created these huge explosion remnants? Speculation has been building recently that outbursts even more powerful than well-known supernovae might occur. Dubbed hypernovae, these explosions might result from high-mass stars and liberate perhaps ten times more energy than conventional supernovae. A hypernova was originally postulated to explain the great amount of energy seemingly liberated in a gamma-ray burst. A search for visible remnants of hypernovae has now yielded the above two candidates. Nearby spiral galaxy M101, shown on the right, has two large expanding shells that might have originated from a hypernova. Remnant NGC 5471B on the upper left and MF83 below were identified by the unusually high amount of X-ray radiation they emit. MF83 is also one of the largest expanding shells ever found. Research continues into the possible nature and visibility of hypernovae and the gas shells they likely leave behind.
1999 April 21
The Nearest Stars
Drawing Credit: T. J. Henry et al., RECONS Team
Which stars are closest to the Sun? The closest is Proxima Centauri, one of three stars that orbit each other about 4 light-years away in the Alpha-Centauri system. Alpha Centauri is easily visible from Earth's Southern Hemisphere. Next is Barnard's Star, a dim star visible with a telescope in the constellation of Ophiuchus. Sirius, the brightest star in the night sky, is part of the fifth closest star system, from which light takes 8.6 years to reach us. The nearest 25 star systems are shown on the above map, out to 13 light-years. Past that there are probably stars so dim that their proximity has not yet been discovered. Research continues in trying to identify an estimated 130 missing star systems out to 32 light-years.
The Nearest Stars
Drawing Credit: T. J. Henry et al., RECONS Team
Which stars are closest to the Sun? The closest is Proxima Centauri, one of three stars that orbit each other about 4 light-years away in the Alpha-Centauri system. Alpha Centauri is easily visible from Earth's Southern Hemisphere. Next is Barnard's Star, a dim star visible with a telescope in the constellation of Ophiuchus. Sirius, the brightest star in the night sky, is part of the fifth closest star system, from which light takes 8.6 years to reach us. The nearest 25 star systems are shown on the above map, out to 13 light-years. Past that there are probably stars so dim that their proximity has not yet been discovered. Research continues in trying to identify an estimated 130 missing star systems out to 32 light-years.
1999 April 22
Where is Upsilon Andromedae?
Credit and Copyright: Till Credner & Sven Kohle
Astronomers recently announced the detection of three large planets orbiting the star Upsilon Andromedae - the first planetary system known to orbit a normal star other than our Sun. These planets were not directly photographed but found through a Doppler technique developed to use large telescopes to search nearby stars for wobbling planetary signatures. However, Upsilon And itself is visible to the unaided eye shining in Earth's sky in the northern constellation Andromeda at about 4th magnitude. This deep photographic image shows Upsilon And along with fainter stars and "deep sky" objects including the famous Andromeda spiral galaxy or M31 (right), the Triangulum galaxy or M33 (below), and the star cluster NGC 752 (left). About 44 light-years distant, Upsilon And is a star only a little more massive and just slightly hotter than the Sun.
Where is Upsilon Andromedae?
Credit and Copyright: Till Credner & Sven Kohle
Astronomers recently announced the detection of three large planets orbiting the star Upsilon Andromedae - the first planetary system known to orbit a normal star other than our Sun. These planets were not directly photographed but found through a Doppler technique developed to use large telescopes to search nearby stars for wobbling planetary signatures. However, Upsilon And itself is visible to the unaided eye shining in Earth's sky in the northern constellation Andromeda at about 4th magnitude. This deep photographic image shows Upsilon And along with fainter stars and "deep sky" objects including the famous Andromeda spiral galaxy or M31 (right), the Triangulum galaxy or M33 (below), and the star cluster NGC 752 (left). About 44 light-years distant, Upsilon And is a star only a little more massive and just slightly hotter than the Sun.
1999 April 23
Io Shadow
Credit: John Spencer (Lowell Observatory), NASA
Orbiting Jupiter once every 43 hours, the volcanic moon Io cruises 500,000 kilometers above swirling, banded cloud-tops. Orbiting Earth once every 1.5 hours, the Hubble Space Telescope watched as Io accompanied by its shadow crossed the face of the reigning gas giant planet in 1997. This and other sharp false-color images have recently been chosen to celebrate the ninth anniversary of the Hubble's launch (April 24, 1990). Reflective patches of sulfur dioxide "frost" are visible on Io's surface while Io's round dark shadow is seen passing over brownish white regions of Jupiter's high altitude haze and clouds. In October and November of this year, the Galileo spacecraft currently operating in the Jovian system is scheduled to make two daring close approaches to Io, possibly flying through a volcanic plume.
Io Shadow
Credit: John Spencer (Lowell Observatory), NASA
Orbiting Jupiter once every 43 hours, the volcanic moon Io cruises 500,000 kilometers above swirling, banded cloud-tops. Orbiting Earth once every 1.5 hours, the Hubble Space Telescope watched as Io accompanied by its shadow crossed the face of the reigning gas giant planet in 1997. This and other sharp false-color images have recently been chosen to celebrate the ninth anniversary of the Hubble's launch (April 24, 1990). Reflective patches of sulfur dioxide "frost" are visible on Io's surface while Io's round dark shadow is seen passing over brownish white regions of Jupiter's high altitude haze and clouds. In October and November of this year, the Galileo spacecraft currently operating in the Jovian system is scheduled to make two daring close approaches to Io, possibly flying through a volcanic plume.
1999 April 24
Barsoom
Credit: The Viking Project, NASA
"Yes, I have been to Barsoom again ..." begins John Carter in Edgar Rice Burroughs' 1913 science fiction classic "The Gods of Mars". In Burroughs' novels describing Carter's adventures on Mars, "Barsoom" is the local inhabitants' name for the Red Planet. Long after Burroughs' stories were published, Mars continues to inspire Earthdwellers' interests and imagination. Soon it will again be invaded by spacecraft from Earth. This dramatic picture of a crescent Mars was taken by NASA's Viking 2 spacecraft in 1976.
Barsoom
Credit: The Viking Project, NASA
"Yes, I have been to Barsoom again ..." begins John Carter in Edgar Rice Burroughs' 1913 science fiction classic "The Gods of Mars". In Burroughs' novels describing Carter's adventures on Mars, "Barsoom" is the local inhabitants' name for the Red Planet. Long after Burroughs' stories were published, Mars continues to inspire Earthdwellers' interests and imagination. Soon it will again be invaded by spacecraft from Earth. This dramatic picture of a crescent Mars was taken by NASA's Viking 2 spacecraft in 1976.
1999 April 25
Mimas: Small Moon with a Big Crater
Credit: Voyager 1, NASA
Mimas is one of the smaller moons of Saturn but shows one of the largest impact craters. In fact, if the impact had been much greater, it would have disrupted the entire satellite. The large crater has been named Herschel after the 1789 discoverer of Mimas, Sir William Herschel. Mimas' low mass produces a surface gravity just strong enough to create a spherical body but weak enough to allow such relatively large surface features. Mimas is made of mostly water ice with a smattering of rock - so it is accurately described as a big dirty snowball. Voyager 1 flew by in 1980 and took the above picture.
Mimas: Small Moon with a Big Crater
Credit: Voyager 1, NASA
Mimas is one of the smaller moons of Saturn but shows one of the largest impact craters. In fact, if the impact had been much greater, it would have disrupted the entire satellite. The large crater has been named Herschel after the 1789 discoverer of Mimas, Sir William Herschel. Mimas' low mass produces a surface gravity just strong enough to create a spherical body but weak enough to allow such relatively large surface features. Mimas is made of mostly water ice with a smattering of rock - so it is accurately described as a big dirty snowball. Voyager 1 flew by in 1980 and took the above picture.
1999 April 26
USNO-A2.0 Catalog: A Digital Sky
Credit: PMM Team, USNO Flagstaff Station
Here lie 526,230,881 of the brightest stars known. The US Naval Observatory has deployed their monster Precision Measuring Machine to digitize photographic plates covering the whole sky and creating the above map. Yellow corresponds to 150,000 stars per square degree, while dark blue corresponds to only 500 stars per square degree. (For comparison, the Full Moon takes up about 1/4 of a square degree.) The most striking feature on this whole sky projection is the central disk of our Milky Way Galaxy, which stretches across the middle. Dark dust lanes are evident there by the great number of stars they obscure. The two bright spots seen south of the Milky Way's disk are the neighboring Magellanic Cloud galaxies. Anyone can order a free copy of this data, but not everyone can fit data from all 526,230,881 stars on their hard-drive.
USNO-A2.0 Catalog: A Digital Sky
Credit: PMM Team, USNO Flagstaff Station
Here lie 526,230,881 of the brightest stars known. The US Naval Observatory has deployed their monster Precision Measuring Machine to digitize photographic plates covering the whole sky and creating the above map. Yellow corresponds to 150,000 stars per square degree, while dark blue corresponds to only 500 stars per square degree. (For comparison, the Full Moon takes up about 1/4 of a square degree.) The most striking feature on this whole sky projection is the central disk of our Milky Way Galaxy, which stretches across the middle. Dark dust lanes are evident there by the great number of stars they obscure. The two bright spots seen south of the Milky Way's disk are the neighboring Magellanic Cloud galaxies. Anyone can order a free copy of this data, but not everyone can fit data from all 526,230,881 stars on their hard-drive.
1999 April 27
Introducing Comet Lee
Credit & Copyright: Gordon Garradd
Another large snowball is falling toward the Sun. Comet Lee was discovered two weeks ago by Steve Lee (AAO) in Australia, and is expected to brighten as it approaches the inner Solar System. Comet Lee is not expected to become a naked-eye object, though, with recent projections guessing it will peak at magnitude 7 in July. Starting in May, the large piece of dirty ice officially known as Comet C/1999 H1 Lee will be visible to northern observers. Comet Lee is the fuzzy patch in the above picture taken on April 16 from Loomberah, Australia.
Introducing Comet Lee
Credit & Copyright: Gordon Garradd
Another large snowball is falling toward the Sun. Comet Lee was discovered two weeks ago by Steve Lee (AAO) in Australia, and is expected to brighten as it approaches the inner Solar System. Comet Lee is not expected to become a naked-eye object, though, with recent projections guessing it will peak at magnitude 7 in July. Starting in May, the large piece of dirty ice officially known as Comet C/1999 H1 Lee will be visible to northern observers. Comet Lee is the fuzzy patch in the above picture taken on April 16 from Loomberah, Australia.
1999 April 28
A Sundial for Mars
Credit: W. Sullivan (U. Washington) et al., Mars Surveyor 2001, NASA
When Mars Surveyor arrives at Mars in 2002, it will carry a sundial. Even though batteries and a solar array will power the Mars Surveyor Lander, the sundial has been included to allow a prominent public display of time. The sundial idea was the brainchild of Bill Nye the Science Guy, who noticed that a post originally used for camera calibration could be redesigned. Millennia ago, sundials were state-of-the-art timekeepers for humans on Earth. Since the Sun casts similar shadows on Mars and Earth, accurate calibration of the shadow placement on the Martian Sundial will tell a curious inspector of returned images both the time of day and the season.
A Sundial for Mars
Credit: W. Sullivan (U. Washington) et al., Mars Surveyor 2001, NASA
When Mars Surveyor arrives at Mars in 2002, it will carry a sundial. Even though batteries and a solar array will power the Mars Surveyor Lander, the sundial has been included to allow a prominent public display of time. The sundial idea was the brainchild of Bill Nye the Science Guy, who noticed that a post originally used for camera calibration could be redesigned. Millennia ago, sundials were state-of-the-art timekeepers for humans on Earth. Since the Sun casts similar shadows on Mars and Earth, accurate calibration of the shadow placement on the Martian Sundial will tell a curious inspector of returned images both the time of day and the season.
1999 April 29
NGC 2266: Old Cluster in the New General Catalog
Credit and Copyright: Till Credner & Sven Kohle, Bonn University, Calar Alto Observatory
The New General Catalog of star clusters and nebulae really isn't so new. In fact, it was published in 1888 - an attempt by J. L. E. Dreyer to consolidate the work of astronomers William, Caroline, and John Herschel along with others into a useful single, complete catalog of astronomical discoveries and measurements. Dreyer's work was successful and is still important today as this famous catalog continues to lend its acronym "NGC" to bright clusters, galaxies, and nebulae. Take for example this star cluster known as NGC 2266 (item number 2,266 in the NGC compilation). It lies about 10,000 light-years distant in the constellation Gemini and represents an open or galactic cluster. With an age of about 1 billion years, NGC 2266 is old for a galactic cluster. Its evolved red giant stars are readily apparent in this gorgeous three-color image.
NGC 2266: Old Cluster in the New General Catalog
Credit and Copyright: Till Credner & Sven Kohle, Bonn University, Calar Alto Observatory
The New General Catalog of star clusters and nebulae really isn't so new. In fact, it was published in 1888 - an attempt by J. L. E. Dreyer to consolidate the work of astronomers William, Caroline, and John Herschel along with others into a useful single, complete catalog of astronomical discoveries and measurements. Dreyer's work was successful and is still important today as this famous catalog continues to lend its acronym "NGC" to bright clusters, galaxies, and nebulae. Take for example this star cluster known as NGC 2266 (item number 2,266 in the NGC compilation). It lies about 10,000 light-years distant in the constellation Gemini and represents an open or galactic cluster. With an age of about 1 billion years, NGC 2266 is old for a galactic cluster. Its evolved red giant stars are readily apparent in this gorgeous three-color image.
1999 April 30
Solar Shock Wave
Credit: Barry Reynolds (Perth, Australia) and the SOHO - EIT Consortium
On September 24, 1997 a shock wave blasted across the surface of the sun at speeds of 250 to 600 kilometers per second. On planet Earth, observer Barry Reynolds photographed the expanding shock front (left) in the light emitted by hydrogen atoms at the solar surface. His discovery image was nicely confirmed by a space-based extreme ultraviolet image (right) of the shock ramming through the sun's upper atmosphere as recorded by the SOHO satellite observatory. In both pictures a bright solar flare is seen near the center of a circular arc-like feature representing a shock front. The shock front is dark in the ground based photo and bright in the ultraviolet image. These shock fronts are believed to be tracers of a 3-dimensional disturbance caused by the flare but researchers are uncertain as to the exact physical mechanisms which produced it. Along with other violent events called coronal mass ejections, solar flares are known to generate streams of energetic particles which can affect the Earth's magnetosphere and Earth orbiting satellites.
Solar Shock Wave
Credit: Barry Reynolds (Perth, Australia) and the SOHO - EIT Consortium
On September 24, 1997 a shock wave blasted across the surface of the sun at speeds of 250 to 600 kilometers per second. On planet Earth, observer Barry Reynolds photographed the expanding shock front (left) in the light emitted by hydrogen atoms at the solar surface. His discovery image was nicely confirmed by a space-based extreme ultraviolet image (right) of the shock ramming through the sun's upper atmosphere as recorded by the SOHO satellite observatory. In both pictures a bright solar flare is seen near the center of a circular arc-like feature representing a shock front. The shock front is dark in the ground based photo and bright in the ultraviolet image. These shock fronts are believed to be tracers of a 3-dimensional disturbance caused by the flare but researchers are uncertain as to the exact physical mechanisms which produced it. Along with other violent events called coronal mass ejections, solar flares are known to generate streams of energetic particles which can affect the Earth's magnetosphere and Earth orbiting satellites.
1999 May 1
Lunar Dust and Duct Tape
Credit: Apollo 17, NASA
Why is the Moon dusty? On Earth, rocks are weathered by wind and water, creating soil and sand. On the Moon, the long history of micrometeorite bombardment has blasted away at the rocky surface creating a layer of powdery lunar soil or regolith. This lunar regolith could be a scientific and industrial bonanza. But for the Apollo astronauts and their equipment, the pervasive, fine, gritty dust was definitely a problem. On the lunar surface in December 1972, Apollo 17 astronauts Harrison Schmitt and Eugene Cernan needed to repair one of their lunar rover's fenders in an effort to keep the "rooster tails" of dust away from themselves and their gear. This picture reveals the wheel and fender of their dust covered rover along with the ingenious application of spare maps, clamps, and a grey strip of "duct tape".
Lunar Dust and Duct Tape
Credit: Apollo 17, NASA
Why is the Moon dusty? On Earth, rocks are weathered by wind and water, creating soil and sand. On the Moon, the long history of micrometeorite bombardment has blasted away at the rocky surface creating a layer of powdery lunar soil or regolith. This lunar regolith could be a scientific and industrial bonanza. But for the Apollo astronauts and their equipment, the pervasive, fine, gritty dust was definitely a problem. On the lunar surface in December 1972, Apollo 17 astronauts Harrison Schmitt and Eugene Cernan needed to repair one of their lunar rover's fenders in an effort to keep the "rooster tails" of dust away from themselves and their gear. This picture reveals the wheel and fender of their dust covered rover along with the ingenious application of spare maps, clamps, and a grey strip of "duct tape".
1999 May 2
Stars from Eagle's Eggs
Credit: J. Hester, P. Scowen (ASU), HST, NASA
Newborn stars are forming in the Eagle Nebula. This image, taken with the Hubble Space Telescope in 1995, shows evaporating gaseous globules (EGGs) emerging from pillars of molecular hydrogen gas and dust. The giant pillars are light years in length and are so dense that interior gas contracts gravitationally to form stars. At each pillars' end, the intense radiation of bright young stars causes low density material to boil away, leaving stellar nurseries of dense EGGs exposed. The Eagle Nebula, associated with the open star cluster M16, lies about 7000 light years away.
Stars from Eagle's Eggs
Credit: J. Hester, P. Scowen (ASU), HST, NASA
Newborn stars are forming in the Eagle Nebula. This image, taken with the Hubble Space Telescope in 1995, shows evaporating gaseous globules (EGGs) emerging from pillars of molecular hydrogen gas and dust. The giant pillars are light years in length and are so dense that interior gas contracts gravitationally to form stars. At each pillars' end, the intense radiation of bright young stars causes low density material to boil away, leaving stellar nurseries of dense EGGs exposed. The Eagle Nebula, associated with the open star cluster M16, lies about 7000 light years away.
1999 May 3
Loop I in the Northern Sky
Credit: ROSAT, MPI, ESA, NASA
One of the largest coherent structures on the sky is known simply as Loop I and can best be seen in radio and X-ray maps. Spanning over 100 degrees, part of Loop I appears so prominent in northern sky maps that it is known as the North Polar Spur (NPS). Loop I, shown above in X-ray light, is a thin bubble of gas about 700 light-years across with a center located only about 400 light-years away. Surprisingly, the cause of this immense structure is still debated, but is possibly related to expanding gas from a million-year old supernova. Loop I gas is impacting the nearby Aquila Rift molecular cloud, and may create relatively dense fragments of the local interstellar medium. Were our Sun to pass through one of these fragments in the next few million years, it might affect Earth's climate.
Loop I in the Northern Sky
Credit: ROSAT, MPI, ESA, NASA
One of the largest coherent structures on the sky is known simply as Loop I and can best be seen in radio and X-ray maps. Spanning over 100 degrees, part of Loop I appears so prominent in northern sky maps that it is known as the North Polar Spur (NPS). Loop I, shown above in X-ray light, is a thin bubble of gas about 700 light-years across with a center located only about 400 light-years away. Surprisingly, the cause of this immense structure is still debated, but is possibly related to expanding gas from a million-year old supernova. Loop I gas is impacting the nearby Aquila Rift molecular cloud, and may create relatively dense fragments of the local interstellar medium. Were our Sun to pass through one of these fragments in the next few million years, it might affect Earth's climate.
1999 May 4
Magnetic Mars
Credit: Jack Connerney, Mario Acuna, Carol Ladd, MGS, NASA
Mapping Mars from orbit, instruments on the Mars Global Surveyor (MGS) spacecraft have recently revealed banded magnetic field patterns - a startling and unanticipated suggestion that the Red Planet was more Earth-like in its distant past. The red and blue regions within the MGS orbital tracks across this portion of southern Mars indicate adjacent areas of crust where magnetic fields point in opposite directions. The bands seem to run east-west and are about 100 miles wide and 600 miles long. Such patterns are known to be produced on Earth by plate tectonics. As the crustal plates spread apart along the mid-ocean ridges, they carry a progressive banded record of Earth's changing magnetic field. The similar patterns on Mars are seen as evidence that it too once had moving crustal plates and a changing magnetic field, although both processes - still active on the larger planet Earth - are thought to have long since died away. These high resolution measurements of martian magnetism were made possible by the revised, close aerobraking orbits of the MGS spacecraft and not originally planned.
Magnetic Mars
Credit: Jack Connerney, Mario Acuna, Carol Ladd, MGS, NASA
Mapping Mars from orbit, instruments on the Mars Global Surveyor (MGS) spacecraft have recently revealed banded magnetic field patterns - a startling and unanticipated suggestion that the Red Planet was more Earth-like in its distant past. The red and blue regions within the MGS orbital tracks across this portion of southern Mars indicate adjacent areas of crust where magnetic fields point in opposite directions. The bands seem to run east-west and are about 100 miles wide and 600 miles long. Such patterns are known to be produced on Earth by plate tectonics. As the crustal plates spread apart along the mid-ocean ridges, they carry a progressive banded record of Earth's changing magnetic field. The similar patterns on Mars are seen as evidence that it too once had moving crustal plates and a changing magnetic field, although both processes - still active on the larger planet Earth - are thought to have long since died away. These high resolution measurements of martian magnetism were made possible by the revised, close aerobraking orbits of the MGS spacecraft and not originally planned.
1999 May 5
A Solar System Portrait
Credit: Voyager 1 Team, NASA
As the Voyager 1 spacecraft headed out of our Solar System, it looked back and took a parting family portrait of the Sun and planets. From beyond Pluto, our Solar System looks like a bright star surrounded by faint dots. In the above picture, the Sun is so bright it is blocked out for contrast. The innermost dots visible, labeled E and V for Earth and Venus, are particularly hard to discern. Gas giants Jupiter (J) and Saturn (S) are much more noticeable. The outermost planets visible are Uranus (U) and Neptune (N). Each planet is shown labeled and digitally enhanced in an inset image. Voyager 1 is only one of four human-made objects to leave our Solar System, the other three being Voyager 2, and Pioneer 10 and Pioneer 11.
A Solar System Portrait
Credit: Voyager 1 Team, NASA
As the Voyager 1 spacecraft headed out of our Solar System, it looked back and took a parting family portrait of the Sun and planets. From beyond Pluto, our Solar System looks like a bright star surrounded by faint dots. In the above picture, the Sun is so bright it is blocked out for contrast. The innermost dots visible, labeled E and V for Earth and Venus, are particularly hard to discern. Gas giants Jupiter (J) and Saturn (S) are much more noticeable. The outermost planets visible are Uranus (U) and Neptune (N). Each planet is shown labeled and digitally enhanced in an inset image. Voyager 1 is only one of four human-made objects to leave our Solar System, the other three being Voyager 2, and Pioneer 10 and Pioneer 11.
1999 May 6
Liberty Bell 7
Credit: Courtesy NASA
Today, the space capsule Liberty Bell 7 rests about 3 miles below the surface of the Atlantic Ocean. But on July 21, 1961, astronaut Virgil I. "Gus" Grissom rode this tiny craft 118 miles above the Earth to become the second American in space. Grissom's flight was suborbital - like fellow Mercury astronaut Alan Shepard's first flight - however his capsule was different, with a window, a new manual spacecraft control system, and an explosive hatch. Unfortunately, after Grissom brought Liberty Bell 7 to a successful splash down in the planned area, the hatch blew prematurely and rough seas began to flood the capsule. While Grissom was able to get out, the military recovery helicopter could not lift the waterlogged spacecraft. This dramatic picture was taken from the helicopter shortly before Liberty Bell 7 was released and sank.
Liberty Bell 7
Credit: Courtesy NASA
Today, the space capsule Liberty Bell 7 rests about 3 miles below the surface of the Atlantic Ocean. But on July 21, 1961, astronaut Virgil I. "Gus" Grissom rode this tiny craft 118 miles above the Earth to become the second American in space. Grissom's flight was suborbital - like fellow Mercury astronaut Alan Shepard's first flight - however his capsule was different, with a window, a new manual spacecraft control system, and an explosive hatch. Unfortunately, after Grissom brought Liberty Bell 7 to a successful splash down in the planned area, the hatch blew prematurely and rough seas began to flood the capsule. While Grissom was able to get out, the military recovery helicopter could not lift the waterlogged spacecraft. This dramatic picture was taken from the helicopter shortly before Liberty Bell 7 was released and sank.