2005 YU55

Et zut, et zut , et zut ... hier soir à 18h, nous étions 8 fêlés au club d'astronomie et pensions fermement que le fait de nous déplacer sur ce lieu ferait partir tous ces nombreux nuages qui sévissaient dans le ciel nancéen. Que nenni. L'espoir fait vivre mais la réalité est frustrante ... couverture nuageuse intense ... même du brouillard. 

Moi qui espérait tant mettre une belle photo de cet astéroïde sur mon blog .. et bien non. Je vais devoir juste me contenter de mettre les différents articles trouvés sur internet en mettant à la poubelle tout ce qui apocalyptique ou débile ... et là c'est fou le nombre de conneries qu'on peut trouver sur la toile ...

Discret passage d’un astéroïde dans la banlieue terrestre ce soir

article de Didier Jamet

L’astéroïde 2005 YU 55 effectuera un passage au large de la Terre ce soir, à une confortable distance de 324 600 km, soit quelque 85% de la distance moyenne Terre-Lune.

Mesurant dans les 400 mètres de diamètre et présentant un aspect quasi sphérique, 2005 YU 55 sera au plus près de notre planète à 0H28 heure de Paris mercredi 9 novembre (23h28 mardi T.U.). Il se trouvera alors non loin de la « queue » de la constellation du Dauphin (voir carte ci contre ou notrecarte du ciel interactive).

Il sera cependant bien trop éloigné de nous pour être visible à l’œil nu, puisque sa magnitude sera de l’ordre de 11, soit 100 fois moins lumineux que le plus faible objet perceptible à l’œil nu. Il faut au moins disposer d’un télescope de 150 mm de diamètre pour espérer l’apercevoir, et encore en sachant exactement où regarder (voir carte ci-contre). Le moment le plus favorable pour le repérer sera sans doute vers 23h30, lorsque l’astéroïde visiteur se trouvera tout proche de la brillante étoile Altaïr de la constellation de l’Aigle. Malheureusement en France, Altaïr sera alors très basse sur l’horizon ouest, à quelques degrés de hauteur, d’où l’importance d’avoir un horizon bien dégagé vers l’ouest.

S’agissant des risques futurs d’impact avec la Terre, 2005 YU55 ne présentera pas plus de danger que ce soir pour au moins les 100 années à venir. Mais les objets géocroiseurs ont des orbites par nature chaotique : il est difficile de prévoir leur évolution au delà d’un horizon assez bref (quelques centaines d’années), alors que les trajectoires des planètes sont elles précisément connues sur plusieurs centaines de millions d’années.

D’où l’intérêt d’étudier attentivement ces corps célestes errants lors de chacun de leurs passages à portée immédiate des radars et des télescopes terrestres les plus puissants afin de mieu connaître leurs caractéristiques. Ce soir, tout le monde sera sur le pont !

site http://www.cidehom.com/astronomie.php?_a_id=497

Mini-Asteroid Makes a House Call

Update Tuesday afternoon: NASA has just released its first radar-image movie of the rotating asteroid. More to come.

Update 10 p.m. EST: S&T's Alan MacRobert writes: "Got it!! Despite thin haze and bright moonlight, I picked it up pretty easily in my 12.5-inch reflector at 85×, and so did my wife Abby, and Keith Murdock visiting from the Rockland (NY) Astronomy Club. We all took turns watching it graze stars and pass through little asterisms. It was precisely dead on target, on the pencil line I drew on Sky & Telescope's finder chart offset for Boston per the instructions. Big thanks to Tony Flanders' spot-on chart-designing skills. It looked a little orange-reddish compared to most stars. Such a tiny thing to be all over the TV news tonight!"

Meanwhile, S&T's Dennis di Cicco imaged the asteroid crossing the stars from his home observatory not far away. He writes, "This chunk of rock was moving! This is just a slapped-together image of several 45-second exposures made as fast as the camera could download the images. Meade 16-inch scope at about f/6.5, SBIG ST-8300 camera, clear filter." The image:

 

Original Story:

Roll out the red carpet! Earth is about to be visited by the largest close-approaching asteroid on record. Known as 2005 YU₅₅, it comes closest to us on November 8th at 23:28 Universal Time (6:28 p.m. EST), when it passes 198,000 miles (319,000 km) from Earth's surface — closer than the Moon's orbit. It will be visible from the Americas and Europe through much of the night.

Discovered nearly six years ago by Robert McMillan at Steward Observatory's Spacewatch Telescope in Arizona, 2005 YU₅₅ has been this way before. In April 2010 it passed close enough for detailed radar probing by the giant radio dish at Arecibo, Puerto Rico.

The Arecibo observations showed this asteroidal emissary to be a quarter mile (400 meters) across and remarkably round. Given its size and dimness, its surface must be quite dark and thus likely carbon-rich. Its rotation period is relatively long, 18 to 20 hours. 

In the grand scheme of things it's more micro-planet than minor planet, but we've never knowingly had something this big come this close before. Were it to strike Earth, 2005 YU₅₅ would deliver a kinetic-energy punch equivalent to several thousand megatons of TNT. It's the kind of potential threat that outer-space sentries lose sleep over.

But fear not: the Arecibo observations allowed dynamicists to recompute the big rock's orbit with enough accuracy to ensure that it won't strike Earth within the next 100 years. (That said, it will pass just 175,000 miles from Venus in 2029, close enough to alter its orbit slightly. This adds uncertainty to predictions for its next close encounter with Earth in 2041, when the minimum distance could be anywhere from 200,000 to 30 million miles.)

So we might as well just enjoy this month's show. The asteroid will approach Earth from the sunward direction, so it will be a daylight object until just before the time of closest approach. A few hours later 2005 YU₅₅ should reach a visual magnitude of 11.1, within reach of backyard telescopes with apertures of at least 6 inches under fairly dark skies — though you'll be fighting light from the nearly full Moon. (By the way, that bright thing near the Moon tonight is Jupiter.)

The pass's track is especially favorable for western Europe and North America. But you'll need to know exactly where to look at exactly what time: the object will traverse the 70° of sky eastward from Aquila to central Pegasus in just 10 hours, clipping along at 7 arcseconds per second. Use the chart here to get a sense of what part of the sky it's in, then download our detailed finder chart for use between 9 and 10 p.m. November 8th Eastern Standard Time (2:00 and 3:00 November 9th Universal Time).

If you don't have a suitable scope, or if it's cloudy tonight, check out thelive video webcast of asteroid 2005 YU55 from the 25-inch telescope at Clay Center Observatory in Massachuetts (continuously from about 6 p.m. to 3 a.m. EST). Another live webcast is available from Bellatrix Astronomical Observatory in Italy. 

Amateur asteroid sleuths Brian Warner and Robert Stephens have mounted a campaign to obtain detailed photometry (brightness measurements) of the asteroid. You'll need at least a 10- or 12-inch scope, a CCD camera, and ideally one or more of the standard photometric filters commonly used by professional astronomers. Details.

Meanwhile, this visit by 2005 YU₅₅ is providing an unprecedented opportunity for high-reolution radar study. Astronomers have lined up extensive radar campaigns with Arecibo and with NASA's Goldstone facility in California's Mojave Desert, using big radio dishes in West Virginia and elsewhere as receivers. "The signal-to-noise ratios will be more than 1 million for Goldstone observations on November 8–9," explains Lance Benner (Jet Propulsion Laboratory). This SNR is heady territory for radar work, high enough to yield thousands of pixels across the object and to achieve surface resolution "comparable to what can be obtained by a spacecraft flyby mission."

So I hope you all get a chance to spot 2005 YU₅₅ as it zips past Earth.

le site http://www.skyandtelescope.com/observing/home/133013563.html