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2007-05-08T14:07:37+02:00

The Brightest Supernova Ever

05.07.2007

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May 7, 2007: The brightest stellar explosion ever recorded may be a long-sought new type of supernova, according to observations by NASA's Chandra X-ray Observatory and ground-based optical telescopes. This discovery indicates that violent explosions of extremely massive stars were relatively common in the early universe, and that a similar explosion may be ready to go off in our own galaxy.

"This was a truly monstrous explosion, a hundred times more energetic than a typical supernova," said Nathan Smith of the University of California at Berkeley, who led a team of astronomers from California and the University of Texas in Austin. "That means the star that exploded might have been as massive as a star can get, about 150 times that of our sun. We've never seen that before."

Above: An artist's illustration of supernova SN 2006gy. [More]

Astronomers think many of the first stars in the Universe were this massive, and this new supernova may thus provide a rare glimpse of how those first generation stars died. It is unprecedented, however, to find such a massive star and witness its death. The discovery of the supernova, known as SN 2006gy, provides evidence that the death of such massive stars is fundamentally different from theoretical predictions.

"Of all exploding stars ever observed, this was the king," said Alex Filippenko, leader of the ground-based observations at the Lick Observatory at Mt. Hamilton, Calif., and the Keck Observatory in Mauna Kea, Hawaii. "We were astonished to see how bright it got, and how long it lasted."

The Chandra observation allowed the team to rule out the most likely alternative explanation for the supernova: that a white dwarf star with a mass only slightly higher than the sun exploded into a dense, hydrogen-rich environment. In that event, SN 2006gy should have been 1,000 times brighter in X-rays than what Chandra detected.

Above: Optical (left) and X-ray (right) images of SN 2006gy. The dimmer source at lower-left is the nucleus of the host galaxy. The brighter source at upper-right is the stellar explosion. The supernova was as bright as the entire core of a galaxy! [More]

"This provides strong evidence that SN 2006gy was, in fact, the death of an extremely massive star," said Dave Pooley of the University of California at Berkeley, who led the Chandra observations.

The star that produced SN 2006gy apparently expelled a large amount of mass prior to exploding. This large mass loss is similar to that seen from Eta Carinae, a massive star in our galaxy, raising suspicion that Eta Carinae may be poised to explode as a supernova. Although SN 2006gy is intrinsically the brightest supernova ever, it is in the galaxy NGC 1260, some 240 million light years away. However, Eta Carinae is only about 7,500 light years away in our own Milky Way galaxy.

"We don't know for sure if Eta Carinae will explode soon, but we had better keep a close eye on it just in case," said Mario Livio of the Space Telescope Science Institute in Baltimore, who was not involved in the research. "Eta Carinae's explosion could be the best star-show in the history of modern civilization."

Right: eta Carinae--a supernova waiting to happen in our own galaxy? The giant star is highlighted by diffraction spikes in this astrophoto taken by Brad Moore. [More]

Supernovas usually occur when massive stars exhaust their fuel and collapse under their own gravity. In the case of SN 2006gy, however, astronomers think that a very different effect may have triggered the explosion. Under some conditions, the core of a massive star produces so much gamma ray radiation that some of the energy from the radiation converts into particle and anti-particle pairs. The resulting drop in energy causes the star to collapse under its own huge gravity.

After this violent collapse, runaway thermonuclear reactions ensue and the star explodes, spewing the remains into space. The SN 2006gy data suggest that spectacular supernovas from the first stars that spew their remains - rather than completely collapsing to a black hole as theorized - may be more common than previously believed.

"In terms of the effect on the early universe, there's a huge difference between these two possibilities," said Smith. "One [sprinkles] the galaxy with large quantities of newly made elements and the other locks them up forever in a black hole."

Tenu par la cuisse de Jupiter, cette Jupiter !!

2007-05-02T10:55:55+02:00




Fantastic Flyby	05.01.2007
+ Play Audio \| + Download Audio \| + Email to a friend \| + Join mailing list May 1, 2007: Today NASA released stunning new images of Jupiter and its moons taken by the New Horizons spacecraft. Views include a movie of a volcanic eruption on Jupiter's moon Io; a nighttime shot of auroras and lava on Io; a color photo of the "Little Red Spot" churning in Jupiter's cloudtops; images of small moons herding dust and boulders through Jupiter's faint rings--and much more: gallery. "We'll be analyzing these data for months to come," says Science Mission Directorate Associate Administrator and New Horizons Principal Investigator Alan Stern of NASA Headquarters. "We have collected spectacular scientific products as well as evocative images." Right: Europa rising over the clouds of Jupiter. The picture was one of a handful of the Jupiter system that New Horizons took primarily for artistic, rather than scientific, value. [More] New Horizons came within 1.4 million miles of Jupiter on Feb. 28 in a gravity assist maneuver designed to trim three years off its travel time to Pluto. For several weeks before and after this closest approach, the piano-sized robotic probe trained its seven cameras and sensors on Jupiter and its four largest moons, storing data from nearly 700 observations on its digital recorders and gradually sending that information back to Earth. About 70 percent of the expected 34 gigabits of data has come back so far, radioed to NASA's largest antennas over more than 600 million miles. This activity confirmed the successful testing of the instruments and operating software the spacecraft will use at Pluto. "Aside from setting up our 2015 arrival at Pluto, the Jupiter flyby was a stress test of our spacecraft and team, and both passed with very high marks," adds Stern. A highlight of the flyby was the first close-up color scan of the Little Red Spot: Above: Jupiter's "Little Red Spot." Credit: New Horizons. [More] This storm is about half the size of Jupiter's larger Great Red Spot and about 70 percent of Earth's diameter. It formed in the late 1990s when three smaller storms collided and merged. The combined storm started out white, but began turning red about a year ago. Using New Horizons data, scientists will be able to search for clues about how these great storm systems form and why they change colors. "This is our best look ever at a storm like this in its infancy," said Hal Weaver, New Horizons project scientist from the Johns Hopkins University Applied Physics Laboratory (APL), Laurel, Md. APL built and operates the New Horizons spacecraft. Under a range of lighting and viewing angles, New Horizons also grabbed the clearest images ever of the tenuous Jovian ring system. In them, scientists spotted a series of unexpected arcs and clumps of dust, indicative of a recent impact into the ring by a small object. Right: Well-defined lanes of gravel- to boulder-sized material in Jupiter's charcoal black rings. Credit: New Horizons. [More] Movies made from New Horizons images also provide an unprecedented look at ring dynamics, with the tiny inner moons Metis and Adrastea appearing to shepherd the materials around the rings. (Scroll to the middle of this page to see the movies.) "We're starting to see that rings can evolve rapidly, with changes detectable during weeks and months," said Jeff Moore, New Horizons Jupiter Encounter science team lead from NASA Ames Research Center, Moffett Field, Calif. "We've seen similar phenomena in the rings of Saturn." Of Jupiter's four largest moons, the team focused much attention on volcanic Io, the most geologically active body in the solar system. New Horizons' cameras captured pockets of bright, glowing lava scattered across the surface; dozens of small, glowing spots of gas; and several fortuitous views of a sunlit umbrella-shaped dust plume rising 200 miles into space from the volcano Tvashtar, the best images yet of a giant eruption from the tortured volcanic moon. Above: Io at night. Visible in the image are volcanic hot spots and an auroral glow, produced as intense radiation from Jupiter's magnetosphere bombards Io's atmosphere. Credit New Horizons. [More] The timing and location of the spacecraft's trajectory also allowed it to spy many of the mysterious, circular troughs carved onto the icy moon Europa. Data on the size, depth and distribution of these troughs, discovered by the Jupiter-orbiting Galileo mission, will help scientists determine the thickness of the ice shell that covers Europa's global ocean. Already the fastest spacecraft ever launched, New Horizons reached Jupiter 13 months after lifting off from Cape Canaveral Air Force Station, Fla., in January 2006. The flyby added 9,000 miles per hour, pushing the velocity of New Horizons past 50,000 miles per hour and setting up a flight by Pluto in July 2015. Right: The Tvashtar volcano on Io. Click here to view a two-frame movie of the plume in action. [More] The number of observations at Jupiter was actually twice that of those planned at Pluto. New Horizons made most of these observations during the spacecraft's closest approach to the planet, which was guided by more than 40,000 separate commands in the onboard computer. "We can run simulations and take test images of stars, and learn that things would probably work fine at Pluto," said John Spencer, deputy lead of the New Horizons Jupiter Encounter Science Team, Southwest Research Institute, Boulder, Colo. "But having a planet to look at and lots of data to dig into tells us that the spacecraft and team can do all these amazing things. We might not have explored the full capabilities of the spacecraft if we didn't have this real planetary flyby to push the system and get our imaginations going." There's more to come: New Horizons is making an unprecedented flight down Jupiter's long magnetotail, where it will analyze the intensities of sun-charged particles that flow hundreds of millions of miles beyond the giant planet. Stay tuned!

2007-04-28T13:54:21+02:00

This Week's Sky at a Glance

by Alan M. MacRobert

Some daily events in the changing sky for April 27 – May 5.

Watch Venus pass between Beta and Zeta Tauri, the horns of Taurus, in the western sky at dusk this week.

Sky & Telescope diagram.

Friday, April 27

A dawn challenge: Uranus appears less than 1° south of Mars on Saturday and Sunday mornings. On Saturday morning (for the Americas), 1st-magnitude Mars, the 4.4-magnitude star Phi Aquarii, and 6th-magnitude Uranus form a little line 0.9° long, in that order from right to left. On Sunday morning, Mars is below the two faint dots.

Try looking with binoculars or a telescope about 75 minutes before sunrise, depending on the clarity of the air. To find your local sunrise time, make sure you've put your location and current time zone into our online almanac.

Saturday, April 28

Look for Spica this evening about two fist-widths at arm's length lower left of the Moon. About the same distance directly below the Moon, look for the four-star, sail-shaped constellation of Corvus, the Crow.

Sunday, April 29

Venus is passing 3° south (lower left) of Beta Tauri this evening and tomorrow evening.

Monday, April 30

Look for Spica shining above the Moon tonight. Far to their upper left shines brighter Arcturus.

Tuesday, May 1

Full Moon tonight (exact at 6:09 a.m. Wednesday morning EDT).

Wednesday, May 2

Now that it's May, can you still catch the Belt of Orion on its way out for the season? As twilight fades, look for it near the horizon far to the lower left of bright Venus. The Belt is nearly horizontal. Above it stands orange-red Betelgeuse, the last of Orion's bright stars to go.

Thursday, May 3

Close to 3rd-magnitude Gamma Bootis lies the red long-period variable star V Bootis, which should be just past maximum light (8th magnitude) this week. See the article and chart in the May Sky & Telescope, page 62, and take a look with binoculars! After you've found V Boo once or twice, you can check in on it at a glance whenever you take binoculars out on a clear night.

Friday, May 4

The waning gibbous Moon shines near Jupiter and Antares from about midnight tonight to dawn Saturday morning. See the dawn view below.

The annual Eta Aquarid meteor shower peaks before dawn Saturday morning; it's observable from the tropics and the Southern Hemisphere. But even there this isn't a good year for the Eta Aquarids, what with the bright moonlight.

Saturday, May 5

As the evening grows late, bright Vega climbs well up in the northeast. Meanwhile bright Arcturus is shining very high in the southeast. Look a third of the way from Vega to Arcturus for the dim Keystone of Hercules. Look two thirds of the way for the dim semicircle of Corona Borealis, the Northern Crown.

The Moon passes Antares and Jupiter in the morning sky as it wanes after full. (These scenes are drawn for the middle of North America. European observers: move each Moon symbol a quarter of the way toward the one for the previous date. The blue 10° scale is about the size of your fist held at arm's length. For clarity, the Moon is shown three times actual size.)

Sky & Telescope diagram.

Want to become a better amateur astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly foldout map in each issue of Sky & Telescope, the essential magazine of astronomy. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of maps; the standard is Sky Atlas 2000.0) and good deep-sky guidebooks (such as Sky Atlas 2000.0 Companion or the enchanting though dated Burnham's Celestial Handbook). Read here how to use them most effectively.

More beginners' tips: "How to Start Right in Astronomy".

This Week's Planet Roundup

Mercury is hidden in the glare of the Sun.

The clouds of Venus are essentially featureless to the eye, but they get more interesting in the ultraviolet. Sky & Telescope's Sean Walker took these stacked video images with a 12.5-inch reflector in excellent seeing before sunset on April 20, 2007. "Here are my two best results," he writes, taken 28 minutes apart. "I picked up a fused silica lens that I fashioned into a barlow — it has excellent UV transmission, though I still needed to add my Astro-Physics Barcon to achieve an acceptable image scale. Still, both together allowed a bright image at 98 frames per second."

S&T: Sean Walker

Venus (magnitude –4.1, in Taurus) is the brilliant "Evening Star" in the west during and after twilight. A few degrees to Venus's right, watch the not-quite-first-magnitude star Beta Tauri moving downward day by day.

Mars (magnitude +1.0, in Aquarius) still remains low in the east-southeast during dawn.

Jupiter (magnitude –2.5, in southern Ophiuchus) rises around 11 p.m. daylight saving time and dominates the south before dawn. Antares, less bright, sparkles 10° to Jupiter's upper right when they rise, and to its lower right by daybreak. There's a lot doing on Jupiter this season; see article. The clearest telescopic views are before and during dawn, when Jupiter is highest.

For public astronomy nights, Saturn remains the evening crowd pleaser. As Saturn approaches eastern quadrature, notice how wide the globe's shadow on the rings (left of globe here) has become.

S&T: Sean Walker

Saturn (magnitude +0.4, at the Leo-Cancer border) shines high in the southwest during evening. Regulus, less bright at magnitude +1.4, is 12° to its left or upper left. North of Regulus is 2.3-magnitude Algieba (Gamma Leonis), a fine telescopic double star.

Uranus (magnitude 6, in Aquarius) is very low in the east-southeast before dawn, in the background of Mars.

Neptune (magnitude 8, in Capricornus) low in the southeast before dawn.

Pluto (magnitude 14, in northwestern Sagittarius) is not far from Jupiter in the south before dawn.

All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's midnorthern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America. Eastern Daylight Time (EDT) equals Universal Time (UT, UTC, or GMT) minus 4 hours.

comme entendu à radio ce matin : allô la terre ici la terre'

2007-04-25T19:55:41+02:00

Gliese 581c, première planète extraterrestre compatible avec la vie

Par Jean Etienne, Futura-Sciences, le 25/04/2007 à 16h04

La découverte autour de l'étoile Gliese 581 (Gl 581) d'une planète extraterrestre marque une étape importante car, pour la première fois, celle-ci réunit toutes les caractéristiques considérées comme indispensables à l'apparition éventuelle d'une forme de vie.

Depuis maintenant douze années, les scientifiques ne cessent de détecter des planètes en dehors de notre Système solaire. Depuis la première découverte par Michel Mayor en 1995, les observations se sont succédées et leur nombre approche à présent les 230.

Mais la plupart n'ont amené que des déceptions. La majorité ne sont que des astres morts, en orbite autour d'un cadavre stellaire qui les a enveloppées de ses rayonnements mortels avant d'agoniser. On connaît aujourd'hui des planètes en orbite autour d'étoiles normales, d'étoiles géantes, d'étoiles naines, d'étoiles doubles, et même d'étoiles triples. On a même observé des planètes solitaires qui ne tournent autour de rien du tout.

On connaît des mondes recelant des traces d'eau, des géantes gazeuses, et même des planètes potentiellement rocheuses comme la nôtre. Certaines ont été photographiées. Mais aucune ne présentait cette dose minimale d'hospitalité qui aurait fait entrevoir une possibilité, même réduite, d'abriter la vie. Aussi la découverte de Gliese 581c représente-t-elle un intérêt exceptionnel.

L'étoile Gliese 581. Crédit ESO.

Les scientifiques disposent maintenant de plusieurs technologies pour mettre en évidence les mondes extraterrestres. Pour Gliese 581c, c'est l'analyse de la vitesse radiale de son étoile qui a été utilisée, sur la base des données obtenues au moyen du télescope Harps (High Accuracy Radial Velocity for Planetary Searcher) de 3,6 mètres de l'observatoire européen (ESO) de la Silla, au Chili. Une planète en orbite imprime à son soleil de légères oscillations par effet gravitationnel, et la mesure de celles-ci permet non seulement d'en détecter la présence, mais encore d'en déterminer la masse, la vitesse de révolution ainsi que la distance à l'étoile. Mais ce n'est pas tout, l'analyse fine de ces données permet aussi de déterminer si ces oscillations sont provoquées par un ou plusieurs objets, et d'en calculer les caractéristiques. On appréciera mieux l'extrême difficulté de mettre ces déplacements en évidence en signalant que dans le cas de Gliese 581, la vitesse radiale mesurée est de 2 à 3 mètres par seconde, soit environ 9 km/heure !

Schémas des vitesses radiales mesurées induites par les trois planètes connues orbitant autour de Gliese 581. En haut, Gliese 581 b, découverte en 2005. Au centre, Gliese 581c et en bas Gliese 581d, qui représente 8 fois la masse de la Terre et dont la vitesse de révolution est de 84 jours. Crédit ESO.

Gliese 581 est une étoile de type naine rouge située à 20,5 années-lumière de nous, dans la constellation de la Balance. Une première planète avait déjà été détectée il y a 2 ans, Gliese 581b, comparable à Neptune (15 fois la masse de notre Terre) et orbitant en 5,4 jours. Gliese 581c, la dernière découverte, tourne en 13 jours seulement à une distance de 11 millions de kilomètres (contre une moyenne approximative de 150 millions de km pour la Terre. Elle mesurerait 1,5 rayon terrestre et sa gravité en surface serait de 2,2 g.

La proximité de la planète par rapport à son étoile pourrait faire conclure un peu trop rapidement à des conditions incompatibles à la vie telle que nous la connaissons. Eh bien non, car cette dernière est une naine rouge, bien moins chaude que notre Soleil, de sorte que la température de surface de la planète est estimée entre 0 et 40°C. Autrement dit, Gliese 581c est parfaitement à même de retenir des océans d'eau liquide, ce solvant indispensable à l'élaboration des matières organiques complexes qui ont permis notre propre émergence.

"En raison de sa température et de sa relative proximité de la Terre, cette planète va devenir très probablement une cible très importante des futures missions spatiales consacrées à la vie extra-terrestre", se réjouit un des auteurs de la découverte, Xavier Delfosse, de l'université de Grenoble.

Une troisième planète, Gliese 581d, orbite également autour de l'étoile, mais sa masse (8 x la Terre) et la distance de son orbite, parcourue en 84 jours, la rend nettement moins propice à la vie.

Commenter cette news ou lire les commentaires

Vue d'artiste de ce que pourrait être Gliese 581c.
Crédits : ESO

Sujets connexes :

Première observation d'eau dans l'atmosphère d'une exoplanète (11/04/07)
Les vents supersoniques des exoplanètes (19/01/07)
Une moisson d'exoplanètes attendue à partir de 2011 grâce à Gaïa (07/09/06)
Exoplanète : découverte d'un système double à 2 planètes, sans étoile ! (07/08/06)
A la recherche des exoplanètes (23/11/04)
Planètes extrasolaires : une nouvelle clé pour comprendre la formation planétaire (17/10/06)

quand un certain 'barman' découvre de l'exo-H20

2007-04-12T10:15:35+02:00

Première observation d'eau dans l'atmosphère d'une exoplanète

Par Jean Etienne, Futura-Sciences, le 11/04/2007 à 16h18

Si aujourd'hui la découverte de planètes en dehors de notre Système solaire ne surprend plus personne, nos connaissances s'affinent sans cesse sur leur nature. Un pas important vient d'être franchi avec la mise en évidence pour la première fois d'eau dans l'atmosphère d'une exoplanète par l'équipe du Pr Travis Barman, astronome à l'observatoire Lowell de Flagstaff, en Arizona.

Afin de permettre cette observation, les astronomes ont utilisé le télescope spatial Hubble et profité d'un passage de HD209458b devant son étoile.

Surnommée Osiris et distante de 150 années-lumière de la Terre dans la constellation de Pégase, la masse de cette planète est de 0,69 et son rayon de 1,32 en comparaison à Jupiter. Cela lui confère une densité de 0,38, inférieure à celle de Saturne, autrement dit il s'agit d'une géante gazeuse qui pourrait flotter dans un océan à sa mesure et sa période de révolution est de 3,52 jours.

Quant à son étoile, HD209458, elle ressemble à notre Soleil dont elle partage la classe de type GOV avec 1,05 masse solaire pour une température de surface de 5942°K.

A plusieurs reprises, Osiris avait déjà fait parler d'elle :

En 1999, première observation du passage d'une exoplanète devant son étoile, et première mise en évidence d'une atmosphère;

En 2003, première observation d'une atmosphère d'hydrogène en cours d'évaporation;

En 2004, première détection d'oxygène et de carbone dans une atmosphère d'exoplanète.

Travis Barman n'est pas surpris de la découverte de vapeur d'eau dans une atmosphère d'exoplanète. Au contraire il se dit confiant, car cette présence avait été pressentie depuis un bon moment, non seulement pour Osiris, mais pour beaucoup d'autres planètes extrasolaires.

Barman signale toutefois que Osiris, par sa nature de géante gazeuse, est peu propice à l'éclosion de la vie, du moins telle que nous la connaissons, mais concède qu'il s'agit d'une pièce importante apportée au puzzle. L'eau, en effet, joue un rôle capital en tant que solvant dans toutes les réactions biochimiques indispensables à l'existence de la vie telle que nous pouvons la concevoir, et cette découverte est considérée comme essentielle par les chercheurs et les exobiologistes.

Reste maintenant à perfectionner nos moyens d'investigation afin de pouvoir, non seulement, réduire la limite d'observation des planètes extrasolaires, mais encore affiner les possibilités d'analyse de leurs atmosphères, ce qui sera fait avec la prochaine génération de satellites astronomiques et de télescopes spatiaux.

Commenter cette news ou lire les commentaires

Vue d'artiste d'Osiris, dont l'atmosphère s'échappe dans l'espace.
Crédits : NASA/JPL.

SUS AUX LUMIERES INUTILES EN TOUT GENRE

2007-03-10T08:59:14+01:00

Bonjour à tous,
>
> Le projet "GLOBE at Night" vient de démarrer et durera jusqu'au 21
mars.
> Il a pour but de cartographier la pollution lumineuse dans le monde
> entier, tout en sensibilisant les gens au problème. La
participation est ouverte à chacun et implique notamment de
nombreuses écoles. L'an passé, plus de 18000 personnes avaient
participé.
>
> Il s'agit simplement de comparer la constellation d'Orion vue
depuis votre point d'observation avec une des cartes disponibles sur
le site du projet et de compléter le rapport d'observation sur le
même site.
>
> Plus d'informations ci-dessous et sur le site du projet
> http://www.globe.gov/GaN/
>
> N'hésitez pas à participer !
>
> Cordialement,
>
> Philippe Demoulin
> _______________________________________________________________
>
> Institut d'Astrophysique et de Géophysique
> allée du VI Août, 17 - Bâtiment B5a Tel : +32 4 366.97.85
> B-4000 Sart Tilman (LIEGE, BELGIUM) Fax : +32 4 366.97.11
>
> mailto:demoulin@...
> http://www.astro.ulg.ac.be/~demoulin
> http://girpas.astro.ulg.ac.be
> _______________________________________________________________
>
> -------- Original Message --------
> Subject: Thousands of Schoolchildren Around the World to Help Map
Light
> Pollution in March (Forwarded)
> Date: Sun, 4 Mar 2007 23:07:21 -0500
> From: Andrew Yee <ayee@...>
> Organization: Jet Propulsion Laboratory - Pasadena CA
> Newsgroups: sci.space.news
> Followup-To: sci.space.policy
>
> Media Relations
> National Center for Atmospheric Research
> University Corporation for Atmospheric Research
> Boulder, Colorado
>
> Contacts For Journalists:
>
> David Hosansky, head of Media Relations
> 303-497-8611
>
> Kirsten Meymaris, UCAR Education and Outreach
> 303-497-2583
>
> March 1, 2007
>
> Thousands of Schoolchildren Around the World to Help Map Light
Pollution in March
>
> BOULDER -- Schoolchildren around the world will gaze skyward after
dark from March 8 to 21, looking for specific constellations and then
sharing their observations through the Internet. The initiative,
called GLOBE at Night, will help scientists map light pollution
around the world while educating participants about the stars.
>
> Now in its second year, GLOBE at Night is a special project of The
GLOBE Program (Global Learning and Observations to Benefit the
Environment), a worldwide science and education program managed by
the University Corporation for Atmospheric Research (UCAR) and
Colorado State University (CSU). Last year, more than 18,000 people
from 96 countries on every continent except Antarctica reported a
total of more than 4,500 observations. This year's event promises to
be even bigger.
>
> "This is an exciting event for schoolchildren, families, and citizen
> scientists across the country and around the world," says Kirsten
Meymaris of UCAR's Office of Education and Outreach, who is the GLOBE
at Night project coordinator. "It brings families together to enjoy
the night sky and to become involved in science. And it also raises
awareness about the impact of artificial lighting on our ability to
see the stars."
>
> GLOBE at Night will last two weeks to improve the odds of observers
> experiencing at least one cloud-free night. Children in overcast
areas who cannot see stars will be able to input data about cloud
conditions instead.
>
> Threat to stargazing
>
> Bright outdoor lighting at night is a growing problem for
astronomical observing programs around the world. By having students
in many places hunt for the same constellation, such as Orion, GLOBE
at Night will allow students to compare their observations with what
others see, giving them a sense of how light pollution varies from
place to place. The young observers will also learn more about the
economic and geographic factors that control light pollution in their
communities and around the world.
>
> GLOBE at Night was inspired in part by a similar project carried
out in Arizona and Chile by the National Optical Astronomy
Observatory and the Centro de Apoyo a la Didactica de la Astronomia,
which are cosponsoring GLOBE at Night. Other cosponsors are the GIS
software and technology firm ESRI and the UCAR-based Windows to the
Universe program.
>
> More details on GLOBE at Night are available on the project Web
site.
>
> The University Corporation for Atmospheric Research manages the
National Center for Atmospheric Research under primary sponsorship by
the National Science Foundation (NSF). Opinions, findings,
conclusions, or recommendations expressed in this publication are
those of the author(s)and do not necessarily reflect the views of the
National Science Foundation.
>
> GLOBE is an interagency program funded by NASA and NSF, and
supported by the U.S. Department of State. It is implemented through
a cooperative agreement among NASA, UCAR, and CSU. Internationally,
GLOBE is a partnership between the United States and more than 100
countries.
>
> Related sites on the World Wide Web:
>
> * GLOBE at Night
> http://www.globe.gov/globeatnight
> * Windows to the Universe
> http://www.windows.ucar.edu/
>
>

et si c'était ça cette fameuse vie éternelle ???

2006-09-02T16:21:23+02:00

La vie éternelle de la poussière d'étoiles

Crédit : NASA/JPL-Caltech/M. Meixner (STScI) & the SAGE Legacy Team

Une nouvelle image du télescope spatial Spitzer aide les astronomes à comprendre comment la poussière d'étoiles est recyclée dans les galaxies.

Le portrait cosmique montre le Grand Nuage de Magellan, une galaxie naine voisine baptisée du nom de Ferdinand Magellan, l'explorateur marin qui a observé l'objet suspect la nuit pendant son voyage historique autour de la Terre. Maintenant, près de 500 ans après le voyage de Magellan, les astronomes étudient la vue de Spitzer de cette galaxie pour en apprendre plus au sujet du voyage circulaire de la poussière d'étoiles, des étoiles vers l'espace et l'inverse.

"Le Grand Nuage de Magellan est comme un livre ouvert," commente le Dr. Margaret Meixner (Space Telescope Science Institute, Baltimore, Md.). "Nous pouvons voir le cycle de vie entier de la matière dans une galaxie dans cette photographie." Meixner est l'auteur principal d'un article sur les résultats, à paraître dans l'édition de Novembre 2006 d'Astronomical Journal.

L'éclatante image en fausses couleurs, une mosaïque d'approximativement 300.000 images différentes, montre une mer bleue centrale d'étoiles parmi un bon nombre de vagues colorées et agités de poussières.

La poussière de l'espace est importante pour fabriquer les étoiles, les planètes et même les gens. Les minuscules particules -- particules de minerais, de glace et des molécules riches en carbone -- sont partout dans l'Univers. Les étoiles en développement et les systèmes solaires consomment constamment de la poussière, tandis que les vieilles étoiles répandent à nouveau la poussière dans l'espace, où un jour elle fournira les ingrédients pour de nouvelles générations d'étoiles.

Spitzer, un observatoire infrarouge satellisant le Soleil, est extrêmement sensible à la lueur infrarouge de la poussière qui survient quand les étoiles se réchauffent. La vue sans précédent de l'observatoire du Grand Nuage de Magellan offre un regard unique à trois escales sur l'éternelle promenade de la poussière à travers une galaxie : dans les enveloppes en effondrement autour des jeunes étoiles ; dispersée dans l'espace entre les étoiles; et dans les enveloppes expulsées de matières de vieilles étoiles.

"Les observations de Spitzer du Grand Nuage de Magellan nous donnent la vue la plus détaillée à ce jour sur la façon dont ce procédé de rétroaction fonctionne dans une galaxie entière," note Meixner. "Nous pouvons mesurer la quantité de poussières consommée et éjectée par les étoiles."

En plus de la poussière, la vue de Spitzer révèle presque un million d'objets jamais vus auparavant, la plupart étant des étoiles dans le Grand Nuage de Magellan. Les étoiles cachées, jeunes et vieilles, sont enfoncées dans les couches de poussières qui bloquent la lumière visible des étoiles mais brillent dans l'infrarouge.

"Nous pouvons maintenant voir les populations de vieilles étoiles et les étoiles qui se forment actuellement," note le co-auteur Dr. Karl Gordon de l'Université de l'Arizona, à Tucson.

Le Grand Nuage de Magellan fait partie de la poignée de galaxies naines qui satellisent notre propre Voie lactée. Il est situé près de la constellation australe de la Dorade (Dorado), à environ 160.000 années-lumière de la Terre. Environ un tiers de la galaxie entière peut être vu dans l'image du Spitzer.

Les astronomes croient qu'il y a approximativement six milliards d'années, pas longtemps avant que notre Système solaire se soit formé, cette galaxie naine a été bouleversée via une rencontre proche avec la Voie lactée. Le chaos résultant a déclenché des sursauts de formations d'étoiles massives similaires à ce qui est supposé se produire dans des galaxies plus primitives à des milliards d'années-lumière. Ceci et d'autres traits de galaxies lointaines, tels qu'une forme irrégulière et une faible abondance de métaux, font du Grand Nuage de Magellan la cible voisine parfaite pour étudier l'Univers lointain.

http://www.spitzer.caltech.edu/Media/releases/ssc2006-17/release.shtml