| Piú viste - Uranus and His Moons |
Oberon-V2-PIA00034_modest.jpgOberon, from 660.000 Km - Voyager 279 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 Uranus79 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' Rings79 visitenessun commento
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Miranda-vg2_2684626.jpgThe "limb" of Miranda79 visitenessun commento
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Uranus-Hurricane00.jpgUranian Hurricane (context image)79 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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UMBRIEL-vg2_p29502-Wunda.jpgUmbriel's extremely unusual surface feature: Wunda Crater (Natural Colors; credits: NASA)79 visiteHere is a closeup systhesis from all the close-ups of Wunda Crater.
It is hard to tell if the craters dug up the bright material, or if they had something to do with the impacts. Maybe it was derived from eruptions or melting caused by impacts.
Or maybe they are some sort of frost left over from impacts.
This issue may not be resolved until another spacecraft observes Umbriel. Here is the best view of Wunda that can be generated with the available data.MareKromium
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VA-Uranus_ Rings-V2-PIA01977_modest.jpgUranus' Rings (1)78 visiteEcco gli Anelli di Urano, dei quali si è sovente parlato, ma senza mai approfondire l'argomento in maniera particolare.
Noi Vi offriamo 3 istantanee provenienti dalla Sonda Voyager 2 e relative a questa ennesima Meraviglia del Cosmo. Non ci sono segni evidenti di anomalie e le immagini, occorre dirlo, non sono di grandissima qualità. Tuttavia, in attesa di nuovi passaggi ravvicinati accanto a questo strano Gigante Gassoso (passaggi, purtroppo, non previsti a breve...), noi guardiamo ancora al passato ed a ciò che abbiamo raccolto negli anni trascorsi.
Il valore storico di queste fotografie è indiscutibile; quello scientifico può essere meglio compreso confrontandole con le immagini ad Alta Definizione degli Anelli di Saturno che ci arrivano - possiamo dire "quotidianamente" - dalla Sonda NASA-ESA Cassini-Huygens.
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VAA-Uranus Rings-1.jpgUranus' Rings (3)78 visiteCiò che intendiamo dire (l'ipotesi di lavoro che Vi proponiamo) è questo: forse gli Anelli di Giove, Urano e di Nettuno hanno un'origine diversa (almeno in parte) rispetto a quelli di Saturno. Gli Scienziati che vanno per la maggiore, infatti, pensano che la differenza nella "tessitura" degli Anelli tipici dei Giganti Gassosi dipenda solo dalle dimensioni originali del corpo celeste (o dei corpi celesti) dal cui disintegrarsi essi vennero generati: più grande era questo/i corpo/i, maggiore era il quantitativo di materiale che si distribuiva lungo l'orbita, più grande e maestosa (scenicamente) risultava la trama finale degli Anelli. Noi opiniamo che, forse, questa costruzione spiega gli Anelli di Giove, Urano e Nettuno ma non è sufficiente - da sola! - per spiegare l'origine degli Anelli di Saturno i quali ci appaiono troppo grandi e troppo complessi per essere derivati soltanto da un evento come quello dianzi ipotizzato.
Ne riparleremo ancora.
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Miranda.jpgExtremely anomalous surface features on Miranda (HR)78 visitenessun commento
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UranusandAriel-Eclypse.jpgUranus and Ariel; Earth and Moon78 visiteCaption NASA originale"This illustrates the relative sizes of Uranus, Earth and Earth's Moon. The images are shown at the proper relative size, but not the correct relative distance from each other. Uranus is approx. 31.000 miles (about 50.000 Km) in diameter, or about 4 times the size of Earth. The Earth is approx. 7.900 miles (about 12.800 Km) in diameter, or about 4 times the diameter of the Moon (2.100 miles, such as about 3.500 Km)".
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VP-URANUS-PIA01360.jpgUranus in natural colors77 visiteCaption NASA originale"These 2 pictures of Uranus were compiled from images recorded by Voyager 2 on Jan. 1O, 1986, when the NASA spacecraft was 18 MKM (11 MMs) from the Planet. The images were obtained by Voyager 2 narrow-angle camera; the view is toward the planet's pole of rotation, which lies just left of center. The picture on the left has been processed to show Uranus as human eyes would see it from the vantage point of the spacecraft. The second picture is an exaggerated false-color view that reveals details not visible in the true-color view - including indications of what could be a polar haze of smog-like particles. The true-color picture was made by combining pictures taken through blue, green and orange filters. The dark shading of the upper right edge of the disk is the terminator, or day-night boundary. The blue-green appearance of Uranus results from methane in the atmosphere; this gas absorbs red wavelengths from the incoming sunlight, leaving the predominant bluish color seen here".
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Uranus-HST-PIA01282.jpgUranus from HST77 visiteThis NASA HST image of Uranus reveals the Planet's Rings and bright clouds and a high altitude haze 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 details, as imaged by the Wide Field Planetary Camera 2, were only previously seen by the Voyager 2 spacecraft, which flew by Uranus in 1986. Since then, none of these inner satellites has been further observed, and detailed observations of the Rings have not been possible.
Though Uranus' Rings were discovered indirectly in 1977 (through stellar occultation observations), they have never before been seen in visible light through a ground-based telescope.
Hubble resolves several of Uranus' Rings, including the outermost Epsilon-Ring. The Planet has a total of 11 concentric Rings of dark dust. Uranus is tipped such that its rotation axis lies in the plane of its orbit, so the Rings appear nearly face-on.
Three of Uranus' inner moons each appear as a string of three dots at the bottom of the picture. This is because the picture is a composite of three images, taken about six minutes apart, and then combined to show the moons' orbital motions. The satellites are, from left to right, Cressida, Juliet, and Portia. The moons move much more rapidly than our own Moon does as it moves around the Earth, so they noticeably change position over only a few minutes.
One of the four gas giant planets of our solar system, Uranus is largely featureless. HST does resolve a high altitude haze which appears as a bright "cap" above the planet's south pole, along with clouds at southern latitudes (similar structures were observed by Voyager). 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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