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Uranus and His Moons
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UT-Uranus Rings.jpgThe new "Giant Rings" of Uranus55 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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Uranus from Keck Obs..jpgUranus from Keck Observatory87 visiteCaption NASA originale:"These sharp views of tilted gas giant Uranus show dramatic details of the planet's atmosphere and ring system. The remarkable ground-based images were made using a near-infrared camera and the Keck Adaptive Optics system to reduce the blurring effects of Earth's atmosphere. Recorded in July 2004, the pictures show two sides of Uranus. In both, high, white cloud features are seen mostly in the northern (right) hemisphere, with medium level cloud bands in green and lower level clouds in blue. The artificial color scheme lends a deep reddish tint to the otherwise faint rings. Because of the severe tilt of its rotational axis, seasons on Uranus are extreme and last nearly 21 Earth years on the distant planet. Uranus is now slowly approaching its southern autumnal equinox - the beginning of fall in the southern hemisphere - in 2007".
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Uranus from Voyager2.jpgUranus from Voyager 284 visiteL'immagine che state osservando venne scattata dalla Sonda Voyager 2 nel 1986. Fu grazie a questa Sonda (l'unica - ad oggi - che sia mai passata nelle vicinanze del Pianeta) che gli Scienziati riuscirono a catturare qualche dettaglio del Sistema di Urano il quale, al pari dei Sistemi di Nettuno, Giove e Saturno, evidenzia l'esistenza di anelli intorno al Pianeta (ma molto sottili e deboli) ed un elevato quantitativo di lune (5 maggiori ed una quindicina minori).
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Uranus-2003.jpgGoing, Going, Gone: Hubble captures Uranus's Rings on Edge (1)54 visiteCaption NASA:"This series of images from NASA's HST shows how the Ring System around the distant planet Uranus appears at ever more oblique (shallower) tilts as viewed from Earth - culminating in the Rings being seen edge-on in 3 observing opportunities in 2007. The best of these events appears in the frame n. 3, taken with Hubble's Wide Field Planetary Camera 2 on August 14, 2007.
The "Edge-On Rings" appear as two spikes above and below the Planet. The Rings cannot be seen running fully across the face of the Planet because the bright glare of the planet has been blocked out in the Hubble photo (a small amount of residual glare appears as a fan-shaped image artifact). A much shorter color exposure of the Planet has been photo-composited to show its size and position relative to the Ring-Plane.
Earthbound astronomers only see Uranus Rings' edge every 42 years as the Planet follows a leisurely 84-year orbit about the Sun. However (and hironically), the last time the Rings were tilted Edge-On to Earth, astronomers didn't even know they existed".MareKromium
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Uranus-2005.jpgGoing, Going, Gone: Hubble captures Uranus' Rings on Edge (2)54 visiteCaption NASA:"With further analysis of the Hubble data, Astronomer Mark Showalter of the SETI Institute in Mountain View, Calif., hopes to detect some of the small moons that may shepherd the debris into distinct rings.
Until Voyager 2 flew by Uranus in January 1986, the Rings were only known from the way they temporarily blocked the light of stars passing behind the Planet. Hubble provided some of the first images of the Ring System as viewed from Earth's distance of approx. 2 BMs.
The advent of adaptive optics gave ground-based observers using large telescopes comparatively sharp views.
The Rings were discovered in 1977, so this is the first time for a Uranus Ring crossing to be observed from Earth. Earth's orbit around the Sun permits 3 opportunities to view the Rings in an "edge-on" configuration: Uranus made its first ring crossing as seen from Earth on May 3; it made its second crossing on August 16 and will cross for the third time on February 20, 2008.
Though the last ring crossing relative to Earth will be hidden behind the Sun, most of Earth's premier telescopes, including Keck, Hubble, the European Southern Observatory's Very Large Telescope and the Hale Telescope on Mt. Palomar, plan to focus on the planet again in the days following December 7, 2007. On December 7 the rings will be perfectly edge-on to the Sun".MareKromium
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Uranus-2007-00.jpgGoing, Going, Gone: Hubble captures Uranus's Rings on Edge (3)54 visiteCaption NASA:"Showalter is a member of a team led by Imke de Pater of the University of California, Berkeley, who reported that the Rings of micron-sized dust have changed significantly since the Voyager 2 spacecraft photographed the Uranus System 21 years ago. Observations were also gleaned from near-infrared adaptive optics observations with the Keck II telescope on May 28, 2007, and reported in an article appearing on August 23 in Science Express, the online edition of Science Magazine".MareKromium
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Uranus-2007-01.jpgGoing, Going, Gone: Hubble captures Uranus's Rings on Edge (4)54 visitenessun commentoMareKromium
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Uranus-HST-CJH.jpgUranus, from HST64 visitenessun commento
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Uranus-HST-PIA01279.jpgUranus from Hubble Space Telescope55 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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Uranus-HST-PIA01282.jpgUranus from HST55 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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Uranus-HST-PIA01283.jpgUranus' Rotation from HST54 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-Hurricane00.jpgUranian Hurricane (context image)54 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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