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| Ultimi arrivi - Asteroids and Comets |
Comets-Comet_Holmes-0.jpgA "Light Arrow" is heading towards "Heart & Soul"...67 visiteCaption NASA:"Two spectacular comets graced Earth's skies during 2007.
Both comets became bright enough to be seen by the unaided eye of the casual sky enthusiast. Early in 2007, Comet McNaught grew brighter than any comet in 40 years, displaying a beautiful dust tail that flowed across the sky.
Comet McNaught (a.k.a. c/2006 P1) became known as the "Great Comet" of 2007, sported unusual striations in its expansive dust tail, and showed unexpectedly complex chemistry in its ion tail.
Toward the year's end, normally docile and faint Comet Holmes brightened suddenly and unexpectedly to naked eye visibility. Remarkably, Comet 17P/Holmes stayed bright for weeks even though it lies beyond the orbit of Mars.
No distant comet in recent history has remained so bright for so long.
In this view, a white Comet Holmes was photographed in early December posing with the Heart and Soul Nebulae".MareKromiumDic 31, 2007
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Comets-Comet_Holmes-UZ-2.jpgComet 17-P-Holmes, from Hungary56 visiteCaption NASA:"Comet Holmes refuses to fade. The unusual comet that surprisingly brightened nearly a million-fold in late October continues to remain visible to the unaided eye from dark locations. Night to night, Comet 17P/Holmes is slowly gliding through the constellation Perseus, remaining visible to northern observers during much of the night right from sunset. Pictured above, Comet Holmes was captured from Hungary last week. The remarkable snowball continues to retain a huge coma, but now shows very little of a tail. To the far right is the open cluster of stars NGC 1245.
How much longer Comet Holmes will remain visible to the unaided eye is unknown".MareKromiumDic 05, 2007
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Comets-Comet_Holmes-UZ-1.jpgComet 17-P-Holmes, from Earth and from HST56 visiteNASA's HST has probed the bright core of Comet 17P/Holmes, which, to the delight of sky watchers, mysteriously brightened by nearly a millionfold in a 24-hour period beginning Oct. 23, 2007.
Astronomers used Hubble's powerful resolution to study Comet Holmes' core for clues about how the comet brightened. The orbiting observatory's Wide Field Planetary Camera 2 (WFPC2) monitored the comet for several days, snapping images on Oct. 29, Oct. 31, and Nov. 4. Hubble's crisp "eye" can see objects as small as 33 miles (54 Km) across, providing the sharpest view yet of the source of the spectacular brightening.
The Hubble image at right, taken Nov. 4, shows the heart of the comet. The central portion of the image has been specially processed to highlight variations in the dust distribution near the nucleus. About twice as much dust lies along the east-west direction (the horizontal direction) as along the north-south direction (the vertical direction), giving the comet a "bow tie" appearance.
The composite color image at left, taken Nov. 1 by an amateur astronomer, shows the complex structure of the entire coma, consisting of concentric shells of dust and a faint tail emanating from the comet's right side.
The nucleus-the small solid body that is the ultimate source of all the comet's activity- is still swaddled in bright dust, even 12 days after the spectacular outburst. "Most of what Hubble sees is sunlight scattered from microscopic particles," explained Hal Weaver of The Johns Hopkins University Applied Physics Laboratory in Laurel, Md., who led the Hubble investigation. "But we may finally be starting to detect the emergence of the nucleus itself in this final Hubble image."
Hubble first observed Comet 17P/Holmes on June 15, 1999, when there was virtually no dusty shroud around the nucleus. Although Hubble cannot resolve the nucleus, astronomers inferred its size by measuring its brightness. Astronomers deduced that the nucleus' diameter was approximately 2.1 miles (3.4 kilometers), about the length of New York City's Central Park. They hope to use the new Hubble images to determine the size of the comet's nucleus to see how much of it was blasted away during the outburst.
Hubble's two earlier snapshots of Comet Holmes also showed some interesting features. On Oct. 29, the telescope spied three "spurs" of dust emanating from the nucleus, while the Hubble images taken on Oct. 31 revealed an outburst of dust just west of the nucleus.
The Hubble images, however, do not show any large fragments near the nucleus of Comet Holmes, unlike the case of Comet 73P/Schwassmann-Wachmann 3 (SW3). In the spring of 2006 Hubble observations revealed a multitude of "mini-comets" ejected by SW3 after the comet increased dramatically in brightness.
Ground-based images of Comet Holmes show a large, spherically symmetrical cloud of dust that is offset from the nucleus, suggesting that a large fragment broke off and subsequently disintegrated into tiny dust particles after moving away from the main nucleus.
Unfortunately, the huge amount of dust near the comet's nucleus and the comet's relatively large distance from Earth (149 million miles, or 1.6 astronomical units, for Holmes versus 9 million, or 0.1 astronomical unit for SW3), make detecting fragments near Holmes nearly impossible right now, unless the fragments are nearly as large as the nucleus itself.
The Hubble Comet Holmes observing team comprises H. Weaver and C. Lisse (The Johns Hopkins University Applied Physics Laboratory); P. Lamy (Laboratoire d'Astrophysique de Marseille, France); I. Toth (Konkoly Observatory, Hungary); M. Mutchler (Space Telescope Science Institute); W. Reach (California Institute of Technology); and J. Vaubaillon (California Institute of Technology).
MareKromiumNov 25, 2007
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Comets-Comet_Holmes-UZ-0.jpgComet 17-P-Holmes, from HST58 visiteCaption NASA:"These images taken by NASA's Hubble Space Telescope reveal Comet Holmes's bright core. The images show that the coma, the cloud of dust and gas encircling the comet, is getting fainter over time. The coma was brightest in the Oct. 29 image. It is two times fainter on Oct. 31 and nine times dimmer on Nov. 4 than during the Oct. 29 observation.
The coma is getting fainter because it is expanding. A huge number of small dust particles was created during the Oct. 23 outburst. Since then those particles have been moving away from the nucleus and filling interplanetary space.
The coma therefore is becoming more diffuse over time.
The nucleus, however, is still active and is producing a significant amount of new dust. So the region around the nucleus is still much brighter (at least 10 times brighter) than it usually is at this point in the comet's orbit.MareKromiumNov 25, 2007
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Comets-Comet_Holmes-UZ-1.gifBigger than the Sun!56 visiteCaption NASA:"The spherical coma of Comet Holmes has swollen to a diameter of over 1,4 MKM, making the tenuous, dusty cloud even bigger than the Sun. Scattering sunlight, all that dust and gas came from the comet's remarkably active nucleus, whose diameter before the late October outburst was estimated to be a mere 3,4 Km.
In this sharp image, recorded on November 14, 2007, with the Canada-France-Hawaii Telescope, stars are easily visible right through the outer coma, while the nucleus is buried inside the condensed, bright region. The bright region of the coma seems offset from the center, consistent with the idea that a large fragment drifted away from the nucleus and disintegrated, producing the comet's spectacular outburst. Of course, more recent images of Holmes also show the bright star Mirfak (Alpha Persei) shining through as the comet sweeps slowly through the constellation Perseus".MareKromiumNov 21, 2007
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Comets-Comet_Holmes-UZ.gifThe Inner Coma of Comet Holmes57 visiteCaption NASA:"What's happening to Comet Holmes?
The rare comet remains visible to the unaided eyes of northern observers as an unusual small puff ball in the constellation of Perseus. A high resolution set of images of the comet's inner coma, taken last week and shown above, reveals significant detail. Close inspection shows numerous faint streamers that are possibly the result of jets emanating from the comet's nucleus. Comet Holmes has remained surprisingly bright over the past week, with luminosity estimates ranging from between visual magnitudes 2 to 3, making it brighter than most stars visible on a dark sky.
The above image of Comet Holmes was made with a small automated 0,38-meter telescope hirable over the web for a small fee".MareKromiumNov 13, 2007
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Comets-Comet_Holmes-UY.jpgComet 17-P-Holmes, from Hungary56 visiteCaption NASA:"A beautiful blue ion tail has become visible in deep telescopic images of Comet Holmes. Pointing generally away from the Sun and also planet Earth, the comet's ion tail is seriously foreshortened by our extreme viewing angle.
Still, enthusiastic comet watchers have remarked that on the whole, the compact but tentacled appearance suggests a jellyfish or even a "cosmic calamaro".
This stunning view of the comet's greenish coma and blue tail was recorded on November 4, 2007, in clear skies near Budapest, Hungary.
The colors are caused by molecules in the tenuous gas, like C2 (green) and CO+ (blue), fluorescing in sunlight". MareKromiumNov 10, 2007
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Comets-Comet_Holmes-UZ.jpgComet 17-P-Holmes, from Italy64 visiteRecent development from 17-P-Holmes: this picture is a deep image from L'Aquila, Italy on November 8, 2007.
It shows the ion tail disconnecting from the comet (just like it happened to the Encke Comet).
MareKromiumNov 10, 2007
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Comets-Comet_Holmes-UX.jpgComet 17-P-Holmes and its - now - Green Coma57 visiteCaption NASA:"This gorgeous skyscape spans some 10° across the Constellation of Perseus, about the size of a generous binocular field of view.
The deep exposure includes bright stars, emission nebulae, star clusters, and, of course, the famous Comet Holmes.
The brightest star in view, Alpha Persei, is itself surrounded by a loose cluster of stars - the Alpha Per Moving Cluster - at a distance of about 600 LY.
But, at a distance of a mere 14 Light-Minutes (LM), bright Comet 17-P-Holmes still dominates the scene with its fluorescing greenish coma and foreshortened blue tail".MareKromiumNov 09, 2007
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LLR-Itokawa-Impacts.jpgThe Craters of Itokawa77 visiteBravissimo, come sempre anche lui, il Dr Marco Faccin il quale, attraverso questo splendido e suggestivo collage, ci mostra e dimostra che, in fondo, NON E' VERO che sul piccolo Asteroide Itokawa non ci sono crateri.
Ci sono, eccome: non molti (e difficilmente discernibili), ma ci sono.
E come mai esistono dei crateri su un mondo che, a parere della NASA, dovrebbe avere una "consistenza" (rectius: densità) bassissima; tanto bassa da farlo risultare, alla fine, come un "mucchio di detriti spaziali tenuti gravitazionalmente assieme"? Un mondo che, laddove impattato da un macigno vagante, dovrebbe - semplicemente - andare in pezzi?
Ebbene la risposta è duplice e (relativamente) facile, a nostro avviso:
1) l'impatto fra Itokawa ed un corpo vagante di dimensioni ridottissime e/o avente una densità bassissima si potrebbe risolvere tranquillamente nella creazione di un cratere poco profondo e di piccole dimensioni;
2) le stime NASA sulla densità di Itokawa sono errate e questo piccolo asteroide - al pari di innumerevoli altri - è un grande macigno errante il quale può sopportare con relativa tranquillità gli impatti con altri corpi vaganti rocciosi e compatti, purchè aventi dimensioni (comunque) modeste.
Avete altre idee? Scriveteci! ...E, per adesso, GRANDI complimenti al bravissimo Dr Faccin!MareKromiumNov 06, 2007
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LLQ-Itokawa-ST_2482160259_v-2.jpgRectangular Surface Feature on Itokawa? (context frame)60 visiteIl bravissimo Dr Gianluigi Barca ha provato a calarsi nei panni di coloro che cercano Anomalìe di Superficie su tutti i Corpi Celesti sino ad ora esplorati (almeno fotograficamente...) e, come lui stesso immaginava, non gli è stato difficile traovare un dettaglio più che meritevole di interesse: nella cerchiatura color fucsia, infatti, "impressa" (diremmo addirittura "scolpita") sulla parte illuminata e rivolta verso lo Spazio di un picco di discrete dimensioni - il quale, per altro, proietta una splendida e ben definita ombra su una delle poche aree "lisce" di Itokawa - è ben visibile un rilievo a forma rettangolare (decisamente di colore più chiaro rispetto alla struttura alla quale esso accede) con possibile apertura alla base (una sorta di piccolo "hangar", si potrebbe dire).
E' un "segno" di attività NON naturale? E' una svista? E' una Singolarità o un'Anomalìa?
Andiamo a vedere il detail-mgnf preparatoci dal Dr Barca stesso...MareKromiumNov 05, 2007
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LLQ-Itokawa-ST_2482160259_v-3.jpgRectangular Surface Feature on Itokawa? (extra-detail mgnf)61 visiteAllora, fermiamoci ai fatti: il "rettangolo" esiste (e si vede bene) ed alla sua base c'è effettivamente qualcosa che non può essere altro che una apertura.
Questo rilievo - che solo un occhio attento al dettaglio poteva individuare - rientra, a nostro parere, nella Classe delle Singolarità Superficiali.
E' un rilievo affascinante, suggestivo, decisamente curioso: certo. Ma quali elementi abbiamo per poter anche solo supporre una sua origine NON naturale?
Nessuno.
L'intero Asteroide Itokawa è un campionario di Singolarità, le quali vanno dalla mancanza di crateri alla presenza, su un buon 75% della sua superficie, di una sorta di "squamatura rocciosa" (si tratta di mini-boulders a forma appuntita ed inclinati - leggermente - rispetto al piano dell'asteroide).
Itokawa (al pari di Phobos, o di 1-Ceres, o di 433-Eros, o al pari delle "unexplainable surface features" di Marte, di Giapeto, di Callisto ed Europa e così via), è una Meraviglia della Natura: è unico, è lontano, è affascinante e, per noi, è largamente inesplicabile.
Parlare di "intervento intelligente" (come sinonimo di "NON naturale") allorchè si analizzano rilievi come questo (o come quelli relativi agli altri Corpi Celesti sopra menzionati), vuol dire - a nostro parere - NEGARE la Capacità Creativa della Natura e, di fatto, significa rifiutarsi di vedere l'Universo per quello che è davvero: una Meravigliosa Opera la quale, per il suo 99,99%, era, è e - probabilmente - rimarrà uno splendido enigma per gli Uomini.
Un enigma che dovrebbe invogliarci a studiare di più e meglio, a capire di più e meglio e ad essere un pochino più umili e consapevoli dei nostri limiti e della attuale nostra incapacità di razionalizzare tutto quello che vediamo e quindi di sussumere l'Ignoto all'interno di Classi di Conoscenza ancora largamente e profondamente imperfette.
Un profondo ringraziamento all'Amico e Collega, Dr Gianluigi Barca, per l'eccezionale "occhio" e per la splendida provocazione che ha lanciato: provocazione che ci ha offerto un eccellente spunto per esprimere un pensiero che, in tanti ormai, avevamo da tempo voglia di tradurre in parole.MareKromiumNov 05, 2007
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