A new image taken by the Hubble Space Telescope shows a large galaxy gobbling up a smaller one; a process anticipated by astronomers, but never directly seen before. Astronomers used the Keck Telescope in Hawaii to confirm that the dwarf galaxy is being consumed by measuring the rate that stars are streaming towards the larger galaxy. The stars of the smaller galaxy will eventually form a spherical halo surrounding the flattened disk of the larger galaxy.
Sea Launch Lofts Echostar IX/Telstar 13
Image credit: Sea Launch
The dual-use Echostar IX/Telstar 13 satellite was successfully placed into orbit Thursday on board a Zenit-3SL which was launched from the Sea Launch platform floating in the middle of the Pacific Ocean. The communications satellite separated 66 minutes after launch, and will eventually provide television services to the United States. This is the tenth launch for Sea Launch, which is expected to have two more launches this year.
Sea Launch, the world?s most reliable launch service provider for heavy commercial communication satellites, today successfully launched the EchoStar IX/Telstar 13 satellite to orbit for EchoStar Communications Corporation and Loral Skynet.
A Zenit-3SL launch vehicle lifted off at 8:31 pm PDT (3:31 GMT) from the Odyssey Launch Platform positioned at 154 degrees West Longitude, on the Equator. All systems performed nominally throughout the flight. The Block DM-SL upper stage inserted the 4,737 kg (10,443 lb) EchoStar IX/Telstar 13 satellite into a high perigee geosynchronous transfer orbit. As planned, the spacecraft?s first signal was acquired at 9:46 pm PDT (4:46 GMT), shortly after spacecraft separation, by a ground station in Western Australia. The spacecraft will be located in geostationary orbit at 121 degrees West Longitude.
Upon completion of the successful mission, Jim Maser, president and general manager of Sea Launch, said, ?I want to congratulate Space Systems/Loral (SS/L), EchoStar Communications Corporation, Loral Skynet and the entire Sea Launch team for a great job! Once again, we achieved a very smooth operation. This is clearly a tribute to the skill, dedication and experience of everyone in the Sea Launch organization and I am very proud to be part of this talented group. We have just completed our second launch in less than two months and we expect to continue this tempo well through next year.
?This mission also marked our tenth launch and the first for SS/L,? Maser continued. ?We appreciate the confidence and trust they and their customers have demonstrated and we look forward to the many more SS/L launches on our manifest. We also welcome the opportunity to serve EchoStar and Loral Skynet in the future.?
SS/L built the EchoStar IX/Telstar 13 spacecraft in Palo Alto, Calif. The Ku-band capacity will enhance EchoStar?s U.S. DISH Network satellite television service. EchoStar has also equipped the spacecraft with the first commercial Ka-band spot-beam payload in the United States. In addition, in a unique multi-band, satellite-sharing arrangement, Loral Skynet will own and operate the satellite?s C-band capacity, as Telstar 13, which will provide television programmers with North American coverage.
Sea Launch Company, LLC, headquartered in Long Beach, Calif., is a world leader in providing heavy-lift commercial launch services. This multinational partnership offers the most direct and cost-effective route to geostationary orbit. With the advantage of a launch site on the Equator, the reliable Zenit-3SL rocket can lift a heavier spacecraft mass or provide longer life on orbit, offering best value plus schedule assurance. Sea Launch has a current backlog of 14 firm launch contracts. For additional information and images of this successfully completed mission, visit the Sea Launch website at: www.sea-launch.com
Original Source: Sea Launch
ESA’s Lunar Mission Prepares for Launch
The European Space Agency’s first spacecraft mission to the Moon, SMART-1, is being prepared for launch at the end of August. The spacecraft was delivered in mid-July to the ESA’s space centre in Kourou, French Guiana, and is expected to launch on August 29. The spacecraft will take 16 months to reach the Moon, following a long spiral trajectory, and using its efficient ion engine to gradually put it into orbit around the Moon. SMART-1 will then search for evidence of water-ice in craters near the Moon’s poles.
Europe?s first probe to the Moon, SMART-1, is about to begin a unique journey that will take it into orbit around our closest neighbour, powered only by an ion engine which Europe will be testing for the first time as main spacecraft propulsion.
The European Space Agency?s SMART-1 spacecraft was delivered to Kourou, French Guiana, on July 15 and is currently being prepared for launch atop an Ariane 5 during the night from August 28 to 29. The launch window will open at 20:04 local time (01:04 on August 29 morning CEST) and will remain open for 26 minutes.
The 367 kg spacecraft will share Ariane?s V162 launch with two commercial payloads: the Indian Space Research Organisation?s Insat 3E and Eutelsat?s e-Bird communication satellites. The smallest spacecraft in the trio, SMART-1, will travel in the lower position, inside a cylindrical adapter, and will be the last to be released.
Europe’s Ariane-5 launcher will put SMART-1 into orbit
A generic Ariane 5 will be in charge of placing these three payloads in a standard geostationary transfer orbit from which each will begin its own journey towards its final operational orbit. SMART-1, powered by its ion engine, will reach its destination in about 16 months, having followed a long spiralling trajectory.
SMART-1?s ion engine will be used to accelerate the probe and raise its orbit until it reaches the vicinity of the Moon, some 350,000 to 400,000 km from Earth. Then, following gravity assists from a series of lunar swingbys in late September, late October and late November 2004, SMART-1 will be ‘captured’ by the Moon?s gravity in December 2004 and will begin using its engine to slow down and reduce the altitude of its lunar orbit.
Testing breakthrough technologies and studying the Moon
SMART-1 is not a standard outer space probe. As ESA?s first Small Mission for Advanced Research in Technology, it is primarily designed to demonstrate innovative and key technologies for future deep space science missions. However, once it has arrived at its destination, it will also perform an unprecedented scientific study of the Moon. SMART-1 is a very small spacecraft (measuring just one cubic metre). Its solar arrays, spanning 14 metres, will deliver 1.9 kW of power, about 75% of which will be used for the probe’s ‘solar electric’ propulsion system.
Close-up view of SMART-1’s stationary plasma thruster
In its role as technological demonstrator, SMART-1?s primary goal is to test this new solar electric propulsion system. This is a form of continuous low-thrust engine that uses electricity derived from solar panels to produce a beam of charged particles that pushes the spacecraft forward. Such engines are commonly called ion engines, and engineers consider them essential for future, long-range space missions. SMART-1 will also test miniaturised spacecraft equipment and instruments, a navigation system that, in the future, will allow spacecraft to autonomously navigate through the solar system, and in addition to a new short-wavelength communication system, a space communication technique by means of which SMART-1 will try to establish a link with the Earth using a laser beam.
Once it enters into a near-polar orbit around the Moon in January 2005, SMART-1 will also become a science platform for lunar observation. SMART-1 will search for signs of water-ice in craters near the Moon?s poles, provide data to shed light on the still uncertain origin of the Moon, and reconstruct its evolution by mapping its topography and the surface distribution of minerals and key chemical elements.
SMART-1 will be the second ESA-led planetary mission to be launched in 2003 after Mars Express in June.
Original Source: ESA News Release
Malfunctioning Instrument on Spirit
An instrument on board Spirit, one of NASA’s Mars Exploration Rovers, has malfunctioned, potentially limiting the amount of data that can be retrieved from the surface of Mars. The instrument is called a Mossbauer spectrometer, and it’s designed to determine the presence and abundance of iron-bearing minerals in the rocks of Mars. If the glitch can’t be worked out, it will still be able to detect the mineral, just not its quantity. Engineers still have several months to get this fixed before Spirit arrives at Mars on January 3.
Asteroids Named for Lost Astronauts
Image credit: NASA
Seven asteroids were recently renamed to honour the astronauts of the space shuttle Columbia. The asteroids are all 5 to 7 km long, and were discovered on the nights of July 19-21, 2001 at the Palomar Observatory near San Diego by astronomer Eleanor F. Helin. NASA’s Jet Propulsion Laboratory proposed the idea, and it was recently approved by the International Astronomical Union, which is responsible for maintaining the names of celestial objects.
The final crew of the Space Shuttle Columbia was memorialized in the cosmos as seven asteroids orbiting the sun between Mars and Jupiter were named in their honor today.
The Space Shuttle Columbia crew– Commander Rick Husband; pilot William McCool; Mission Specialists Michael Anderson, Kalpana Chawla, David Brown, Laurel Clark; and Israeli payload specialist Ilan Ramon, will have celestial memorials, easily found from Earth.
The names, proposed by NASA’s Jet Propulsion Laboratory, Pasadena, Calif., were recently approved by the International Astronomical Union. The official clearinghouse of asteroid data, the Smithsonian Astrophysical Observatory’s Minor Planet Center, released the dedication today.
The seven asteroids were discovered at the Palomar Observatory near San Diego on the nights of July 19-21, 2001, by former JPL astronomer Eleanor F. Helin, who retired in July 2002. The seven asteroids range in diameter from five to seven kilometers (3.1 to 4.3 miles). The Palomar Observatory is owned and operated by the California Institute of Technology, Pasadena.
“Asteroids have been around for billions of years and will remain for billions more,” said Dr. Raymond Bambery, Principal Investigator of JPL’s Near-Earth Asteroid Tracking System. “I like to think that in the years, decades and millennia ahead people will look to the heavens, locate these seven celestial sentinels and remember the sacrifice made by the Columbia astronauts.?
The 28th and final flight of Columbia (STS-107) was a 16-day mission dedicated to research in physical, life and space sciences. The seven astronauts aboard Columbia worked 24 hours a day, in two alternating shifts, successfully conducting approximately 80 separate experiments. On February 1, 2003, the Columbia and its crew were lost over the western United States during the spacecraft’s re-entry into Earth’s atmosphere.
Asteroids are rocky fragments left over from the formation of the solar system about 4.6 billion years ago. Most of the known asteroids orbit the Sun in a belt between Mars and Jupiter. Scientists think there are probably millions of asteroids, ranging in size from less than one kilometer (.62 mile) wide to hundreds of kilometers across.
More than 100,000 asteroids have been detected since the first was discovered back on January 1, 1801. Ceres, the first asteroid discovered, is also the largest at about 933 kilometers (580 miles) in diameter.
The Near-Earth Asteroid Tracking System is managed by JPL for NASA’s Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology.
Information about JPL’s Near-Earth Asteroid Tracking System is available at http://neat.jpl.nasa.gov. More information on the newly named asteroids is at http://www.jpl.nasa.gov/releases/2003/columbia-tribute.cfm.
For information about NASA on the Internet, visit: http://www.nasa.gov.
Original Source: NASA/JPL News Release
Hubble Looks at Our Closest Cluster
Image credit: Hubble
The newest image from the Hubble Space Telescope reveals one of the nearest globular star clusters, NGC 6397, located only 8,200 light years away in the constellation Ara. The stars in this cluster are packed one million times more densely than our own galactic neighborhood; collisions between stars occur every few million years. Two colliding stars may merge to become a “blue straggler”; a bright, young hot star that looks very different from the rest of the stars in the cluster.
This Hubble Space Telescope view of the core of one of the nearest globular star clusters, called NGC 6397, resembles a treasure chest of glittering jewels. The cluster is located 8,200 light-years away in the constellation Ara.
Here, the stars are jam-packed together. The stellar density is about a million times greater than in our Sun’s stellar neighborhood. The stars are only a few light-weeks apart, while the nearest star to our Sun is over four light-years away.
The stars in NGC 6397 are in constant motion, like a swarm of angry bees. The ancient stars are so crowded together that a few of them inevitably collide with each other once in a while. Near misses are even more common. Even so, collisions only occur every few million years or so. That’s thousands of collisions in the 14-billion-year lifetime of the cluster.
These Hubble images were taken for a research program aimed at studying what is left behind when such collisions and near misses occur. When direct collisions occur, the two stars may merge to form a new star called a “blue straggler”; these hot, bright, young stars stand out among the old stars that make up the vast majority of stars in a globular cluster. Several such bright blue stars are visible near the center of the cluster in the Hubble Heritage image.
If two stars come close enough together without actually colliding, they may “capture” each other and become gravitationally bound. One type of binary that might form this way is a “cataclysmic variable”? a pairing of a normal, hydrogen-burning star and a burned-out star called a white dwarf. In a binary system, the white dwarf will pull material off the surface of the normal star. This material encircles the white dwarf in an “accretion disk,” and eventually falls onto it. The result of this accretion process is that cataclysmic variables are, as the name suggests, variable in brightness. The heat generated by the accreting material also generates unusual amounts of ultraviolet and blue light.
To search for cataclysmic variables, the program consisted of a series of 55 images of the cluster taken over a period of about 20 hours. Most of the images were taken in ultraviolet and blue filters; a few images were also taken at green and infrared wavelengths. By comparing the brightness of all the stars in all the images, the Hubble astronomers were able to identify several cataclysmic variable stars in the cluster. Comparison of their brightness in the different filters confirmed that they were emitting copious amounts of ultraviolet light. A few of these stars can be seen in the Hubble Heritage image as faint blue or violet stars.
One of the more intriguing results of this study was completely unexpected. Three faint blue stars can be seen near the center of the cluster ? in the Hubble Heritage image they appear turquoise. These three stars don’t vary in brightness at all, and were clearly not cataclysmic variables. These stars may be very-low-mass white dwarfs, formed in the cores of giant stars whose evolution is somehow interrupted before a full-fledged white dwarf has time to form.
Such an interruption might occur as the result of a stellar collision or an interaction with a binary companion. When a giant star interacts with another star, it can lose its outer layers prematurely, compared to its normal evolution, exposing its hot, blue core. The end result will be a white dwarf of a smaller mass than would have otherwise ensued. In any case, these unusual stars are yet more evidence that the center of a dense globular cluster is a perilous place to reside.
A large number of normal white dwarfs were also identified and studied. These stars appear throughout the cluster, since they form through normal stellar evolution processes and don’t involve any stellar interactions, which occur predominantly near the cluster center. Nearly 100 such burned-out stars were identified in these images, the brightest of which can be seen here as faint blue stars.
This Hubble image is a mosaic of two sets of images taken several years apart by the Wide Field Planetary Camera 2. Archival data from science teams led by Jonathan Grindlay (Harvard University) and Ivan King (University of California, Berkeley), taken in 1997 and 1999, were combined with Hubble Heritage data taken in 2001. Adrienne Cool (San Francisco State University), who was also on both archival science teams, worked with the Hubble Heritage team to acquire the new observations.
Original Source: Hubble News Release
Planning a Mars Party?
With Mars the closest it’s going to be in 60,000 years on August 27, I figure this’ll be a good time to get people interested in space and astronomy. Several astronomers have told me they’re planning to take their telescopes into parks, etc, and give people a chance to see the Red Planet with their own eyes.
I think this is a great idea, so I figured I’ll start maintaining a list on Universe Today of all locations around the world that will have telescopes set up on the 27th.
Is your astronomy club planning a get together for Mars 2003? Let me know where you’re going to be and I’ll add you to the list. Then I’ll make it available as the event gets closer so people can find you and take a look through your telescopes. Even if you’re not part of a club, just take your telescope out to the park, and encourage the public to take a look. Sidewalk astronomy is one of the best ways that astronomers can share their hobby.
Send me an email at [email protected]
Thanks!
Fraser Cain
Publisher
Universe Today
Astronomers Measure the Shape of a Supernova
Image credit: ESO
New data gathered by the European Southern Observatory’s Very Large Telescope (VLT) seems to indicate that supernovae might not be symmetrical when they explode – their brightness changes depending on how you look at them. This discovery is important, because astronomers use supernovae as an astronomical yardstick to measure distances to objects. If they’re brighter or dimmer depending on how you’re looking at them, it could cause errors in your distance calculations. But the new research indicates that they become more symmetrical over time, so astronomers just need to wait a little while before doing their calculations.
An international team of astronomers [2] has performed new and very detailed observations of a supernova in a distant galaxy with the ESO Very Large Telescope (VLT) at the Paranal Observatory (Chile). They show for the first time that a particular type of supernova, caused by the explosion of a “white dwarf”, a dense star with a mass around that of the Sun, is asymmetric during the initial phases of expansion.
The significance of this observation is much larger than may seem at a first glance. This particular kind of supernova, designated “Type Ia”, plays a very important role in the current attempts to map the Universe. It has for long been assumed that Type Ia supernovae all have the same intrinsic brightness, earning them a nickname as “standard candles”.
If so, differences in the observed brightness between individual supernovae of this type simply reflect their different distances. This, and the fact that the peak brightness of these supernovae rivals that of their parent galaxy, has allowed to measure distances of even very remote galaxies. Some apparent discrepancies that were recently found have led to the discovery of cosmic acceleration.
However, this first clearcut observation of explosion asymmetry in a Type Ia supernova means that the exact brightness of such an object will depend on the angle from which it is seen. Since this angle is unknown for any particular supernova, this obviously introduces an amount of uncertainty into this kind of basic distance measurements in the Universe which must be taken into account in the future.
Fortunately, the VLT data also show that if you wait a little – which in observational terms makes it possible to look deeper into the expanding fireball – then it becomes more spherical. Distance determinations of supernovae that are performed at this later stage will therefore be more accurate.
Supernova explosions and cosmic distances
During Type Ia supernova events, remnants of stars with an initial mass of up to a few times that of the Sun (so-called “white dwarf stars”) explode, leaving nothing behind but a rapidly expanding cloud of “stardust”.
Type Ia supernovae are apparently quite similar to one another. This provides them a very useful role as “standard candles” that can be used to measure cosmic distances. Their peak brightness rivals that of their parent galaxy, hence qualifying them as prime cosmic yardsticks.
Astronomers have exploited this fortunate circumstance to study the expansion history of our Universe. They recently arrived at the fundamental conclusion that the Universe is expanding at an accelerating rate, cf. ESO PR 21/98, December 1998 (see also the Supernova Acceleration Probe web page).
The explosion of a white dwarf star
In the most widely accepted models of Type Ia supernovae the pre-explosion white dwarf star orbits a solar-like companion star, completing a revolution every few hours. Due to the close interaction, the companion star continuously loses mass, part of which is picked up (in astronomical terminology: “accreted”) by the white dwarf.
A white dwarf represents the penultimate stage of a solar-type star. The nuclear reactor in its core has run out of fuel a long time ago and is now inactive. However, at some point the mounting weight of the accumulating material will have increased the pressure inside the white dwarf so much that the nuclear ashes in there will ignite and start burning into even heavier elements. This process very quickly becomes uncontrolled and the entire star is blown to pieces in a dramatic event. An extremely hot fireball is seen that often outshines the host galaxy.
The shape of the explosion
Although all supernovae of Type Ia have quite similar properties, it has never been clear until now how similar such an event would appear to observers who view it from different directions. All eggs look similar and indistinguishable from each other when viewed from the same angle, but the side view (oval) is obviously different from the end view (round).
And indeed, if Type Ia supernova explosions were asymmetric, they would shine with different brightness in different directions. Observations of different supernovae – seen under different angles – could therefore not be directly compared.
Not knowing these angles, however, the astronomers would then infer incorrect distances and the precision of this fundamental method for gauging the structure of the Universe would be in question.
Polarimetry to the rescue
A simple calculation shows that even to the eagle eyes of the VLT Interferometer (VLTI), all supernovae at cosmological distances will appear as unresolved points of light; they are simply too far. But there is another way to determine the angle at which a particular supernova is viewed: polarimetry is the name of the trick!
Polarimetry works as follows: light is composed of electromagnetic waves (or photons) which oscillate in certain directions (planes). Reflection or scattering of light favours certain orientations of the electric and magnetic fields over others. This is why polarising sunglasses can filter out the glint of sunlight reflecting off a pond.
When light scatters through the expanding debris of a supernova, it retains information about the orientation of the scattering layers. If the supernova is spherically symmetric, all orientations will be present equally and will average out, so there will be no net polarisation. If, however, the gas shell is not round, a slight net polarisation will be imprinted on the light.
“Even for quite noticable asymmetries, however, the polarisation is very small and barely exceeds the level of one percent”, says Dietrich Baade, ESO astronomer and a member of the team that performed the observations. “Measuring them requires an instrument that is very sensitive and very stable. ”
The measurement in faint and distant light sources of differences at a level of less than one percent is a considerable observational challenge. “However, the ESO Very Large Telescope (VLT) offers the precision, the light collecting power, as well as the specialized instrumentation required for such a demanding polarimetric observation”, explains Dietrich Baade. “But this project would not have been possible without the VLT being operated in service mode. It is indeed impossible to predict when a supernova will explode and we need to be ready all the time. Only service mode allows observations at short notice. Some years ago, it was a farsighted and courageous decision by ESO’s directorate to put so much emphasis on Service Mode. And it was the team of competent and devoted ESO astronomers on Paranal who made this concept a practical success”, he adds.
The astronomers [1] used the VLT multi-mode FORS1 instrument to observe SN 2001el, a Type Ia supernova that was discovered in September 2001 in the galaxy NGC 1448, cf. PR Photo 24a/03 at a distance of 60 million light-years.
Observations obtained about a week before this supernova reached maximum brightness around October 2 revealed polarisation at levels of 0.2-0.3% (PR Photo 24b/03). Near maximum light and up to two weeks thereafter, the polarisation was still measurable. Six weeks after maximum, the polarisation had dropped below detectability.
This is the first time ever that a normal Type Ia supernova has been found to exhibit such clear-cut evidence of asymmetry.
Looking deeper into the supernova
Immediately following the supernova explosion, most of the expelled matter moves at velocities around 10,000 km/sec. During this expansion, the outermost layers become progressively more transparent. With time one can thus look deeper and deeper into the supernova.
The polarisation measured in SN 2001el therefore provides evidence that the outermost parts of the supernova (which are first seen) are significantly asymmetric. Later, when the VLT observations “penetrate” deeper towards the heart of the supernova, the explosion geometry is increasingly more symmetric.
If modeled in terms of a flattened spheroidal shape, the measured polarisation in SN 2001el implies a minor-to-major axis ratio of around 0.9 before maximum brightness is reached and a spherically symmetric geometry from about one week after this maximum and onward.
Cosmological implications
One of the key parameters on which Type Ia distance estimates are based is the optical brightness at maximum. The measured asphericity at this moment would introduce an absolute brightness uncertainty (dispersion) of about 10% if no correction were made for the viewing angle (which is not known).
While Type Ia supernovae are by far the best standard candles for measuring cosmological distances, and hence for investigating the so-called dark energy, a small measurement uncertainty persists.
“The asymmetry we have measured in SN 2001el is large enough to explain a large part of this intrinsic uncertainty”, says Lifan Wang, the leader of the team. “If all Type Ia supernovae are like this, it would account for a lot of the dispersion in brightness measurements. They may be even more uniform than we thought.”
Reducing the dispersion in brightness measurements could of course also be attained by increasing significantly the number of supernovae we observe, but given that these measurements demand the largest and most expensive telescopes in the world, like the VLT, this is not the most efficient method.
Thus, if the brightness measured a week or two after maximum was used instead, the sphericity would then have been restored and there would be no systematic errors from the unknown viewing angle. By this slight change in observational procedure, Type Ia supernovae could become even more reliable cosmic yardsticks.
Theoretical implications
The present detection of polarised spectral features strongly suggests that, to understand the underlying physics, the theoretical modelling of Type Ia supernovae events will have to be done in all three dimensions with more accuracy than is presently done. In fact, the available, highly complex hydrodynamic calculations have so far not been able to reproduce the structures exposed by SN 2001el.
More information
The results presented in this press release have been been described in a research paper in “Astrophysical Journal” (“Spectropolarimetry of SN 2001el in NGC 1448: Asphericity of a Normal Type Ia Supernova” by Lifan Wang and co-authors, Volume 591, p. 1110).
Notes
[1]: This is a coordinated ESO/Lawrence Berkeley National Laboratory/Univ. of Texas Press Release. The LBNL press release is available here.
[2]: The team consists of Lifan Wang, Dietrich Baade, Peter H?flich, Alexei Khokhlov, J. Craig Wheeler, Daniel Kasen, Peter E. Nugent, Saul Perlmutter, Claes Fransson, and Peter Lundqvist.
Original Source: ESO News Release
Perseid Meteor Shower Next Week
Image credit: ESA
The annual Perseid meteor shower is due to make its appearance in mid-August this summer. The shower began on July 23 and will end on August 22, but the bulk of shooting stars will appear on August 13, when upwards of one meteor per minute is visible in the night sky. Unfortunately, the full Moon will brighten the sky and make some of the fainter meteors harder to see. To get the best view of the Perseids, get away from the city lights to a place which is as flat as possible to give you a wide view of the sky.
A fantastic, free light show occurred in the morning of Wednesday, 13 August 2003, in the form of the Perseid meteor shower!
This impressive set of shooting stars appears in the skies every year from around 23 July to 22 August, with its peak on 13 August. First recorded as long ago as 36 AD, the Perseids are also known as ‘the tears of St. Lawrence’ after the Roman martyr.
Typically, you can see this phenomenon with the naked eye, with a shooting star appearing every minute until about 03.00 CET on Wednesday morning. You may also see meteors a few days before or after this time.
However, this year the Moon will be full near the Perseid’s maximum, which will reduce observed rates by a factor of three or so. It will not be until around 2007 when the Moon’s phase is more favourable than that of last year.
Meteor showers occur when the Earth passes through the trail of debris often left behind by a comet. By studying meteor showers, scientists can learn more about cometary debris, but ESA is going a step further with its Rosetta comet-chasing mission which will examine a comet at close range.
Comets are considered to be the primitive building blocks of the Solar System, and the Rosetta mission could help us to understand if life on Earth began with the help of ‘comet seeding’.
The meteors we see are actually tiny bits of comet debris, most of which are only as big as a grain of sand, so they do not pose a threat to us. However, they do provide a spectacular light show as they vaporise on entering the Earth’s atmosphere. This particular shower is named after the Perseus constellation because the shooting stars can appear to start there, but the material was actually shed by the Comet Swift-Tuttle.
To get the best view of the light show, get as far away from city lights as you can since these affect your ability to see the meteor shower.
Make sure that you are comfortable – gazing at the sky for hours can cause neck strain. Find a reclining garden chair or lay out a blanket on the ground. The meteors can appear in any part of the sky, so make sure that you have as wide a view of it as possible.
However, if poor weather prevents you seeing this spectacular show, or you simply cannot stay awake that long, do not give up. You have a chance to view another set of shooting stars in November 2003 when the Leonid meteor shower comes our way. In the third week of November, the Leonids will appear – though 2002 was supposed to be their last big show for the next 30 years.
The Leonids are the leftovers from Comet 55P/Tempel-Tuttle, and ESA scientists regularly conduct intense observation campaigns of these to understand more about comets and cometary debris.
Original Source: ESA News Release
Asteroid Juno Has a Chunk Out of It
Image credit: Harvard
New images taken by the 100-inch Hooker telescope at Mount Wilson Observatory show Asteroid Juno with a huge chunk taken out of it. Harvard astronomer Sallie Baliunas used the adaptive optics system on the Hooker telescope, which compensates for distortions in the atmosphere, to take photos of the 241 km asteroid with incredible clarity. The photos show that Juno is misshapen and has a 100 km crater from an impact with another asteroid in the past.
Cambridge, MA -If someone sneaks a bite of your chocolate chip cookie, they leave behind evidence of their pilferage in the form of a crescent of missing cookie. The same is true in our solar system, where an impact can take a bite out of a planet or moon, leaving behind evidence in the form of a crater. By combining modern technology with a historical telescope, astronomers have discovered that the asteroide Juno has a bite out of it. The first direct images of the surface of Juno show that it is scarred by a fresh impact crater.
Juno, the third asteroid ever discovered, was first spotted by astronomers early in the 19th century. It orbits the Sun with thousands of other bits of space rock in the main asteroid belt between Mars and Jupiter. One of the largest asteroids, at a size of 150 miles across, Juno essentially is a leftover building block of the solar system.
Astronomer Sallie Baliunas (Harvard-Smithsonian Center for Astrophysics) and colleagues photographed Juno when it was located relatively nearby in astronomical terms, about 10 percent further from the Earth than the Earth is from the Sun. Even at that distance, Juno appeared very tiny in the sky, subtending only 330 milli-arcseconds – the equivalent of a dime seen at a distance of 7 miles. Imaging Juno at the high resolution needed to resolve surface details thus presented a challenge.
To solve the problem, the scientists used an adaptive optics system connected to the 100-inch Hooker telescope at Mount Wilson Observatory. Adaptive optics enables astronomers to compensate for the distortion created by air currents in our planet’s atmosphere, yielding images as sharp and clear as those taken in space.
Their surface maps showed that Juno, like other asteroids, is misshapen rather than round, and that it has “sharp” edges. Even better, as Juno tumbled through space during the night of observing, a “bite” came into view – an area that appeared dark as seen at near-infrared wavelengths. The astronomers concluded that the asteroid had recently (in astronomical terms) collided with another object, resulting in a 60-mile-wide crater, or possibly a smaller crater that is surrounded by a 60-mile blanket of ejecta debris.
“I look at an asteroid as a garden – a garden not of flowers and leaves, but one of rubble and dust churned up by constant impacts. This process of gardening pulverizes the asteroid’s surface into a fine-grained regolith,” said Baliunas. “The recent, large impact on Juno gives us an opportunity to see through the regolith and study excavated material from beneath the surface – a rare look into the material out of which the early Earth was formed.”
The blast that knocked a bite out of Juno may also have provided researchers with a convenient way of studying that asteroid up close without ever leaving our planet. Some meteorites found on the Earth are actually pieces of large asteroids like Juno. Those pieces were broken off and launched into space by an impact, and then fell on our planet. The newly-found impact crater on Juno may have sent samples of that asteroid to the Earth.
This remarkable result demonstrates how technology can be used to renew historical observatories, giving them a new lease on life. The Hooker telescope, now nearing the end of its first century of observing, can use adaptive optics systems to obtain views of the cosmos as clear as though the telescope were in space. Hence, the telescope that Edwin Hubble and his assistant used to discover evidence of the expanding universe continues to make groundbreaking discoveries today.
These results were published in the May 2003 issue of the astronomy journal Icarus.
Original Source: CfA News Release