| Piú viste - Uranus and His Moons |
Oberon-V2-PIA01352_modest.jpgOberon, from far away...84 visiteOberon, la Luna Maggiore di Urano: la più esterna e la più grande.
In questa immagine (a differenza della precedente che, ad oggi, è la migliore disponibile!) la Sonda Voyager 2 era ancora troppo lontana da Oberon per catturarne i segreti (la fotografia è stata scattata da una distanza di circa 2.700.000 Km!), ma alcuni dettagli delle sua superficie (i quali peraltro evidenziano una scarsissima albedo: Oberon, in effetti, riflette - in media - circa il 20% della luce solare che riceve) appaiono già con una certa chiarezza.
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Uranus-HST-PIA01279.jpgUranus from Hubble Space Telescope84 visiteCaption NASA originale:"Uranus is sometimes called the sideways planet, because its rotation axis tipped more than 90° from the planet's orbit around the Sun. The year on Uranus lasts 84 Earth years, which creates extremely long seasons - winter in the Northern Hemisphere has lasted for nearly 20 years. Uranus has also been called bland and boring, because no clouds have been detectable in ground-based images of the planet. Even to the cameras of the Voyager spacecraft in 1986, Uranus presented a nearly uniform blank disk and discrete clouds were detectable only in the Southern Hemisphere. Voyager flew over the Planet's cloud tops near the dead of northern winter (when the northern hemisphere was completely shrouded in darkness).
Two images are shown here. The "aqua" image (on the left) is taken at 5,470 Angstroms, which is near the human eye's peak response to wavelength. Color has been added to the image to show what a person on a spacecraft near Uranus might see. Little structure is evident at this wavelength, though with image-processing techniques, a small cloud can be seen near the planet's northern limb (rightmost edge). The "red" image (on the right) is taken at 6,190 Angstroms, and is sensitive to absorption by methane molecules in the planet's atmosphere. The banded structure of Uranus is evident, and the small cloud near the northern limb is now visible".
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Miranda-B.JPGThe "Chevron Grooves" of Miranda (perspective view)84 visitenessun commentoMareKromium
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UMBRIEL-vg2-SV.jpgUmbriel's most prominent Surface Features: Skynd and Wunda Craters (Natural Colors; credits: NASA)84 visiteThe surface of Umbriel is an ancient one.
A collection of impact craters of various sizes was found to saturate the landscape. As Voyager 2 drew closer, became clear that most or all of the bright features are related to craters. On the Terminator, one can see 2 interesting craters.
One, Skynd, has a bright Central Peak. The other, Wunda, at the top of the image, has a bright rim and no apparent Central Peak. This is the best color image obtained by Voyager 2.MareKromium
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Uranus-uppatm-PIA01488.jpgHaze in the upper atmosphere of Uranus83 visiteCaption NASA originale:"This is a computer enhancement of a Voyager 2 image, that emphasizes the high-level haze in Uranus' upper atmosphere. Notice how the clouds are obscured by the overlying atmosphere".
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VB-Uranus-EpsilonRing-V2-PIA01983_modest.jpgUranus' Rings (4) - the "Epsilon Ring"82 visitenessun commento
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VC-Belinda-V2.jpgBelinda - Voyager 282 visiteEd ora una carrellata relativa ad alcune delle Lune "minori" di Urano. La maggior parte di esse è stata scoperta ex-post, cioè analizzando le immagini mandateci alcuni anni fa dai nostri Messaggeri inviati ai confini del Sistema Solare: le Sonde Voyager 1 e 2. Si tratta di mondi assai minuscoli, dalle forme irregolari, probabilmente non originari del Sistema di Urano, ma "catturati" dal Gigante Gassoso in epoche più o meno remote. Forse, queste Lune minori, sono delle "comete mancate" o forse sono frammenti, schegge di corpi celesti più grandi entrati in collisione quando il Sistema Solare era ancora - relativamente - "giovane". Qualunque sia la verità (che, probabilmente, non conosceremo mai), noi Vi offriamo le immagini che abbiamo raccolto in giro per la Rete e desideriamo ringraziare l'Ing. Calvin J. Hamilton, creatore e curatore del bellissimo Sito conosciuto come "Views of the Solar System".
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VM-Sycorax.jpgSycorax82 visitenessun commento
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Oberon-V2-PIA00034_modest.jpgOberon, from 660.000 Km - Voyager 282 visiteCaption NASA originale:"This Voyager 2 picture of Oberon is the best the spacecraft acquired of Uranus' outermost moon. The picture was taken shortly after 3:30 a.m. PST on Jan. 24, 1986, from a distance of 660.000 Km. The color was reconstructed from images taken through the narrow-angle camera's violet, clear and green filters. The picture shows features as small as 12 Km on the moon's surface. Clearly visible are several large impact craters in Oberon's icy surface surrounded by bright rays similar to those seen on Jupiter's moon Callisto. Quite prominent near the center of Oberon's disk is a large crater with a bright central peak and a floor partially covered with very dark material. This may be icy, carbon-rich material erupted onto the crater floor sometime after the crater formed. Another striking topographic feature is a large mountain (vedi il frame "Oberon's Peak"), about 6 km high, peeking out on the lower left limb".
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UT-Uranus Rings.jpgThe new "Giant Rings" of Uranus82 visiteEven though the Voyager 2 spacecraft paid a close-up visit to Uranus in 1986, the distant planet continues revealing surprises to the eye of NASA's HST. HST's high sensitivity and sharp view has uncovered a pair of Giant Rings girdling the Planet. The largest is twice the diameter of the Planet’s previously known Ring System, first discovered in the late 1970s. Hubble also spied two small satellites, named Mab and Cupid. One of the satellites shares an orbit with the outermost of the new Rings. The satellite is probably the source of fresh dust that keeps replenishing the ring with new material knocked off the satellite from meteoroid impacts. Without such replenishment, the dust in the ring would slowly spiral in toward Uranus. Collectively, these new discoveries mean that Uranus has a youthful and dynamic system of Rings and Moons (...) Uranus's Rings are mostly dust (...)".
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VAA-Uranus Rings.2jpg.jpgBeautiful Starfield, through Uranus' Rings82 visitenessun commento
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Uranus-Hurricane00.jpgUranian Hurricane (context image)82 visiteCaption NASA originale:"Just as we near the end of the hurricane season in the Atlantic Ocean, winds whirl and clouds churn 2 BMs away in the atmosphere of Uranus, forming a dark vortex large enough to engulf two-thirds of the United States.
Lawrence Sromovsky of the University of Wisconsin-Madison leads a team that used NASA's HST to take the first definitive images of a dark spot on Uranus. The elongated feature measures 1.100 by 1.900 miles (such as about 1.700 by 3.000 Km).
There have been prior unconfirmed sightings of dark spots on Uranus, including sketches made in the early 1900s, low-contrast ultraviolet Voyager spacecraft flyby images in 1986, and near-infrared observations taken from a ground-based Observatoryin 1993. However, no other HST images taken almost every Summer from 1994 up to 2006 have shown such a dark spot.
This indicates that the current dark disturbance probably formed very recently (...)".
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