| Piú viste - Uranus and His Moons |
Uranus-Neptune-HST3_.JPGUranus and Neptune, from HST (Natural Colors and Enhanced Natural Colors; credits: NASA)87 visitenessun commentoMareKromium
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AB-Ariel-V2-PIA01351.jpgAriel, from 2,52 MKM86 visiteCaption NASA originale:"Distinct bright patches are visible on Ariel, the brightest of Uranus' 5 largest satellites. Voyager 2 obtained this image Jan. 22, 1986, from a distance of 2,52 MKM (1,56 MMs). The clear-filter image, obtained with the narrow-angle camera, shows a resolution of 47 Km (approx. 29 miles). This image shows several distinct bright areas that reflect nearly 45% of the incident sunlight; on average, the satellite displays a reflectivity of about 25-30%. The bright areas are probably fresh water ice, perhaps excavated by impacts. The South Pole of Ariel is slightly off center of the disk in this view. Voyager 2 obtained its best views of the satellite on Jan. 24, 1986 at a closest-approach distance of about 127.000 km (approx. 79.000 mi)".
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Uranus-HST-PIA01283.jpgUranus' Rotation from HST86 visiteThese 3 NASA HST images of the planet Uranus reveal the motion of a pair of bright clouds in the Planet's Southern Hemisphere, and a high altitude haze that forms a "cap" above the Planet's South Pole.
Hubble's view was obtained on August 14, 1994, when Uranus was 1,7 BM (about 2,8 BKM) from Earth. These atmospheric details were only previously seen by the Voyager 2 spacecraft, which flew by Uranus in 1986. Since then, detailed observations of Uranus's atmospheric features have not been possible because the Planet is at the resolution limit of ground-based telescopes.
Hubble's Wide Field Planetary Camera 2 observed Uranus through a filter that is sensitive to light reflected by a pair of high altitude clouds. This makes a high altitude haze over Uranus' south polar region clearly visible, along with a pair of high altitude clouds or plume-type features that are 2500 and 1800 miles (4300 and 3100 kilometers) across, respectively. This sequence of images shows how the clouds (labeled A and B) rotate with the planet during the three hours that elapsed between the first two observations (left and center picture) and the five hours that elapsed between the second pair of observations (center and right picture). Some cloud motion might be due to high altitude winds on the planet. (Observations are indicated in Universal Time.)
By tracking the motion of high-altitude clouds, the new Hubble observations will allow astronomers to make new measurements of Uranus' rotation period. Based on the previous Voyager observations, Uranus spins on its axis at a faster rate than Earth does, completing one rotation every 7 hours, 14 minutes.
One of the four gas giant planets of our solar system, Uranus is largely featureless. Unlike Earth, Uranus' south pole points toward the Sun during part of the planet's 84-year orbit. Thanks to its high resolution and ability to make observations over many years, Hubble can follow seasonal changes in Uranus's atmosphere, which should be unusual given the planet's large tilt.
The Wide Field/Planetary Camera 2 was developed by the Jet Propulsion Laboratory and managed by the Goddard Spaced Flight Center for NASA's Office of Space Science.
MareKromium
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Uranus-2007-01.jpgGoing, Going, Gone: Hubble captures Uranus's Rings on Edge (4)86 visitenessun commentoMareKromium
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Miranda-PIA02218.jpgNot only Verona Rupes: more deep scarps on Miranda (HR)85 visiteCaption NASA originale:"View of Miranda showing light and dark banded scarps near the boundary of the banded ovoid and a deep graben that bounds the ovoid in this region".
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UranusfromHST-3.JPGUranus, from HST (Natural, but enhanced, Colors; credits: NASA)85 visitenessun commentoMareKromium
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UMBRIEL.jpgFarewell Umbriel! (Natural Colors; credits: Ted Stryk)85 visitenessun commentoMareKromium
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ZA-Uranus-IP-V2-PIA00346_modest.jpgFarewell Uranus... (1)82 visiteCaption NASA originale:"This image shows a crescent Uranus, a view that Earthlings never witnessed until Voyager 2 flew near and then beyond Uranus on January 24, 1986. The hazy blue-green atmosphere probably extends to a depth of around 5.400 miles, where it rests above what is believed to be an icy or liquid mixture (an 'ocean') of water, ammonia, methane and other volatiles, which in turn surrounds a rocky core, perhaps a little smaller than Earth".
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Miranda-A86-7026_a.jpgMiranda (possible natural colors; credits: Lunexit)82 visitenessun commentoMareKromium
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UranusfromHST-4.JPGUranus, from HST (Natural, but enhanced, Colors; credits: NASA)82 visitenessun commentoMareKromium
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UranusfromHST-1.JPGUranus, from HST (False Colors; credits: NASA)82 visitenessun commentoMareKromium
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VA-Uranus_ Rings-V2-PIA01985_modest.jpgUranus' Rings (2)81 visiteGli Anelli di Urano, come appare del tutto evidente sin dalla prima istantanea, sono molto più sottili e "deboli" rispetto a quelli di Saturno. In realtà, l'effetto "scenico" delle due serie di anelli è incomparabile: quelli di Saturno sono - come possiamo vedere ogni giorno - un autentico capolavoro di Ingegneria Celeste il quale in parte utilizza, per il suo "equilibrio", anche le delicate risonanze di alcune Lune minori. Gli Anelli di Urano (al pari di quelli di Nettuno), invece, appaiono possedere una natura - oltre che un'apparenza - diversa.
Essi, infatti, potrebbero essere effettivamente la semplice (e anche la sola) conseguenza della disintegrazione di un corpo celeste (un satellite? Un asteroide?) avvicinatosi troppo ad Urano ed i cui residui sono rimasti in orbita attorno ad esso. E' questa, a nostro avviso, la "chiave di lettura" (o almeno una di esse) per comprendere una parte dei misteri dei "Signori degli Anelli".
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