| Piú viste - Asteroids and Comets |
Itokawa-06.jpgOrbiting around Itokawa (3)59 visiteSpecifically, at the time of arrival at Itokawa, Hayabusa had driven its proprietary new ion engines for 26.000 hours, including their operation during an Earth flyby.
It has also perfectly completed a period of hybrid optical navigation followed by
precise guidance and navigation of the spacecraft during its station keeping period around Itokawa.
These engineering achievements are the primary mission of Hayabusa and their successful completion is a great achievement.
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Comets-Comet_Pojmanski-2.jpgThe "Pojmanski" Comet59 visiteE' passata inosservata, lontana dalla nostra Terra, ed è stata ben lungi dall'essere spettacolare come lo fu, qualche anno fa, la meravigliosa Hale-Bopp.
Certo, la cometina Pojmanski non aveva - forse - i numeri giusti per entrare nell'Albo delle (cosiddette) Grandi Comete, ma certo è che i media (TUTTI!) se ne sono guardati bene dal pubblicizzarla. E la NASA? Leggerete Voi stessi le scarne note prodotte al riguardo nel "NASA - Picture of the Day" del giorno 6 Marzo 2006. Noi, nel nostro piccolo, dato che ci meravigliamo per niente, siamo andati in cerca di fotografie di questa cometa ed abbiamo "scoperto" una straordinaria somiglianza fra C/2006 A1 (la Pojmanski Comet appunto) e la C/2004 Q2 (meglio nota come Machholz Comet). Uguale tipologia - o classe visuale - di appartenenza (nucleo sferico e chioma filiforme) e, soprattutto, uguale colore (ergo uguale - o comunque molto simile - composizione chimica). Deduzione logica: si tratta di "Sister-Comets". Domanda: ci sono altre "sorelle" in arrivo?!?
Have you ever seen a comet? Comets bright enough to be visible to the unaided eye appear only every few years. Right now, however, a new comet has brightened unexpectedly and is visible as a faint streak to the unaided northern observer in the eastern morning sky just before sunrise. Binoculars may help. Comet Pojmanski, officially designated C/2006 A1 and discovered only in January, now sports a turquoise tail several times longer than the full moon. Comet Pojmanski's ion tail is due to gas particles expelled by the comet being pushed away from the Sun by the solar wind, the same wind that ionizes gas in the tail causing its blue tint. Pictured above as it appeared only last week, Comet Pojmanski has now begun to fade as its orbit around the Sun takes it further from the Earth.
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Comets-Comet_SWAN-2.jpgComet SWAN59 visiteCaption NASA originale:"Near its closest approach to planet Earth, comet SWAN (C/2006 M4) brightened unexpectedly earlier this week, becoming visible to naked-eye observers under dark night skies. Telescopic observers also noticed dramatic changes in the comet's colorful coma and tail, seen in this view recorded on October 25th, 2006.
To make the picture, images totaling eight minutes in exposure time were stacked and centered on the comet as it moved relatively quickly against the background star field. The picture covers about 1° of the sky.
Northern Hemisphere observers should still find the comet an easy binocular target in the early evening, even though moonlight will increase the overall sky brightness in the next few days.
Look toward the North-Western horizon and the Constellation Hercules".
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McNaught-06.jpgComet McNaught (7)59 visitenessun commento
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MATHILDE_FLY-BY.gifMathilde (NEAR Probe Fly-By)59 visiteGuardate bene: osservate il "main crater" di Mathilde, così (enorme-mente) simile allo Stickney Crater di Phobos e poi, se volete, provate a pensare...Crateri troppo grandi, per mondi troppo piccoli!
Che ne dite?MareKromium
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LLO-Itokawa-ST_25326292LL77_v.jpgThe unbelievable surface of 25143-Itokawa (HR1 - possible natural colors; elab. Lunexit)59 visitenessun commentoMareKromium
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Comets-Comet_Holmes-TView.jpgTelescopic View of the Comet Holmes59 visiteCaption NASA, da "NASA - Picture of the Day" del 29 Ottobre 2007:"What's happened to Comet Holmes? A normally docile comet discovered over 100 years ago, Comet 17P/Holmes suddenly became nearly one million times brighter last week, possibly over just a few hours. In astronomical terms, the comet brightened from magnitude 17, only visible through a good telescope, to magnitude 3, becoming visible with the unaided eye. Comet Holmes had already passed its closest to the Sun in 2007 May outside the orbit of Mars and was heading back out near Jupiter's orbit when the outburst occurred. The comet's sudden brightening is likely due to some sort of sunlight-reflecting outgassing event, possibly related to ice melting over a gas-filled cavern, or possibly even a partial breakup of the comet's nucleus. Pictured above through a small telescope, Comet Holmes appeared as a fuzzy yellow spot, significantly larger in angular size than Earth-atmosphere blurred distant stars. Although Comet Holmes' orbit will place it in northern hemisphere skies for the next two years, whether it will best be viewed through a telescope or sunglasses remains unknown".MareKromium
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Comets-Comet_Holmes-UX.jpgComet 17-P-Holmes and its - now - Green Coma59 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".MareKromium
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Comets-Comet_Holmes-UZ-0.jpgComet 17-P-Holmes, from HST59 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.MareKromium
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Comets-Comet_Holmes-UZ-1.jpgComet 17-P-Holmes, from Earth and from HST59 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).
MareKromium
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EROS-PIA02905-1.jpgEros (Position of the BIG Pseudo-Anomaly)59 visitenessun commentoMareKromium
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Steins-1.JPG2867 Šteins (3D)59 visitenessun commentoMareKromium
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