| Piú viste - Neptune and His Moons |
AA-Neptune-HST-PIA01287_modest.jpgNeptune from HST88 visiteLa seconda serie di immagini del Pianeta Nettuno, ripreso dal Telescopio Spaziale Hubble. Poco da aggiungere rispetto a quanto già detto in precedenza se non che la (quasi totale) impossibilità di fotografare amatorialmente Nettuno dalle nostre latitudini dipende da un continuo e costante degrado dell'atmosfera che ci circonda: inquinamento gassoso ed inquinamento luminoso fanno a gara per vedere quale dei due sia il peggiore.
Purtroppo, sebbene per motivi ed in ambiti diversi, sono entrambi "letali"!
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Neptune-PIA01982.jpgClouds near the "Eye" of Neptune (Natural Colors; credits: Lunexit)87 visiteCaption NASA:"The bright cirrus-like clouds of Neptune change rapidly, often forming and dissipating over periods of several to tens of hours. In this sequence, Voyager 2 observed cloud evolution in the region around the Great Dark Spot (GDS).
The surprisingly rapid changes which occur separating each panel shows that in this Region Neptune's weather is perhaps as dynamic and variable as that of the Earth. However, the scale is immense by our standards -- the Earth and the GDS are of similar size -- and in Neptune's frigid Atmosphere, where temperatures are as low as 55 degrees Kelvin (-360 F), the cirrus clouds are composed of frozen Methane rather than Earth's crystals of water ice".MareKromium
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Neptune-PIA09927.jpgThe "Hot" South Pole of Neptune85 visiteCaption NASA:"These thermal images show a "hot" South Pole on the Planet Neptune. These warmer temperatures provide an avenue for Methane to escape out of the deep atmosphere.
The images were obtained with the Very Large Telescope in Chile, using an imager/spectrometer for mid-infrared wavelengths on Sept. 1 and 2, 2006.
The telescope is operated by the European Organization for Astronomical Research in the Southern Hemisphere (known as ESO).
Scientists say Neptune's South Pole is "hotter" than anywhere else on the Planet by about 10° Celsius (50 degrees Fahrenheit). The average temperature on Neptune is about -200° Celsius (-392 degrees Fahrenheit).
The upper left image samples temperatures near the top of Neptune's troposphere (near 100 millibar pressure, which is 1/10th the Earth atmospheric pressure at sea level). The hottest temperatures are indicated at the lower part of the image, at Neptune's south pole (see the graphic at the upper right).
The lower two images, taken 6.3 hours apart, sample temperatures at higher altitudes in Neptune's stratosphere. They do show generally warmer temperatures near, but not at, the south pole. They also show a distinct warm area which can be seen in the lower left image and rotated completely around the back of the planet and returned to the earth-facing hemisphere in the lower right image".MareKromium
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Neptune-HST1.JPGViews of Neptune (from Hubble Space Telescope)84 visitenessun commentoMareKromium
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Triton-clouds-PIA02203.jpgClouds on the limb of Triton82 visiteCaption NASA originale:"Limb clouds over Triton's South Polar Cap. Image is stretched to enhance the limb clouds and surface features. The image shows the cloud on the west limb that extends about 100 Km along the limb and appears detached over much of its length".
Nuvole nel cielo di Tritone: non si tratta di un'ipotesi affascinante, bensì di un fatto. Ora la domanda non può che essere questa: qual'è la composizione delle nuvole di Tritone?
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PROTEUS.jpgProteus81 visiteUna luna minore del Sistema di Nettuno: Proteus.
Caratterizzata da una forma solo vagamente sferica, questa luna presenta un gigantesco - e facilmente visibile - cratere da impatto in prossimità del suo Polo Nord (fotografico).
Forse è proprio questo cratere la "cicatrice" generata dall'urto che ha spinto "Proteus" al di fuori dalla Fascia di Kuiper e poi verso Nettuno, dalla cui gravità è stato infine catturato.
Un probabilissimo KBO, dunque, o - come dicono alcuni - un Trans Neptunian Object.
O forse una cometa mancata.
Forse.
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Neptune-PIA02209_modest.jpgNeptune from 176.000.000 Km - Voyager 281 visiteCaption NASA originale:"These pictures of Neptune were obtained by Voyager 2 on April 26,1989, at a distance of 176 MKM. At the center of the Neptune disc, each pixel covers a square 4° by 4° in latitude. (Each Voyager image contains 800 pixels, picture elements, per line and 800 lines.) Resolution here was 3256 Km per line pair. The violet, clear and orange filters of Voyager's narrow-angle camera were used to produce the color pictures. Image processing enhances contrast of the features. The picture on the right was taken five hours after that at left, during which time the planet rotated 100°. The dark spot visible in the left picture appeared in clear filter images obtained three months earlier. A much brighter, white spot, prominent in the earlier images, has now apparently faded. The white spot near the south pole in the right picture is new. It was visible only faintly in a picture taken 18 hours earlier at the same longitude. This evidence of dynamic activity was unexpected in Neptune's atmosphere because Neptune receives only one-tenth of one percent as much solar energy as does the Earth".
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Neptune-PIA00048.jpgNeptune in true colors, from Voyager 279 visiteOriginal caption:"This image of clouds in Neptune's atmosphere is the first that tests the accuracy of the weather forecast that was made eight days earlier (nota: questa caption è relativa all'Estate del 1989) to select targets for the Voyager narrow angle camera. Three of the four targeted features are visible in this photograph; all 3 are close to their predicted locations.
The "Great Dark Spot" with its bright white companion is slightly to the left of center. The small bright "Scooter" is below and to the left, and the second "Dark Spot" with its bright core is below the Scooter. Strong eastward winds up to 400 mph cause the second dark spot to overtake and pass the larger one every five days. The spacecraft was 6,1 MKM (about 3,8 MMs) from the Planet at the time of camera shuttering, and the images uses the orange, green and clear filters of the camera".
Qualche nota sui Voyager 1 e 2: Voyager 1, launched September 5, 1977, visited Jupiter in 1979 and Saturn in 1980. It is now leaving the solar system, rising above the ecliptic plane at an angle of about 35 degrees, at a rate of about 520 million kilometers a year.
Voyager 2, launched August 20, 1977, visited Jupiter in 1979, Saturn in 1981 and Uranus in 1986 before making its closest approach to Neptune on August 25, 1989. Voyager 2 traveled 12 years at an average velocity of 19 kilometers a second (about 42,000 miles an hour) to reach Neptune, which is 30 times farther from the Sun than Earth is. Voyager observed Neptune almost continuously from June to October 1989. Now Voyager 2 is also headed out of the solar system, diving below the ecliptic plane at an angle of about 48 degrees and a rate of about 470 million kilometers a year.
Both spacecraft will continue to study ultraviolet sources among the stars, and their fields and particles detectors will continue to search for the boundary between the Sun's influence and interstellar space. If all goes well, we will be able to communicate with the two spacecraft for another 20 years, until their radioactive power sources can no longer supply enough electrical energy to power critical subsystems.
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Neptune-StrechedNaturalColors.JPGNeptune and a few of His Moons (Voyager 2 - Natural, but enhanced, Colors; credits: NASA)78 visiteCaption NASA:"Voyager 2 was the first spacecraft to observe the planet Neptune and its two satellites: Triton, the largest, and Nereid.
The most obvious feature of the Planet is its blue color, the result of Methane in the Atmosphere. Research continues on Neptune's two largest satellites and the additional 6 that were discovered by Voyager 2's investigation". MareKromium
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AA-Neptune-CJH.jpgSmiling Neptune and soft, white, water-clouds - from Voyager 2 (HR)77 visiteUn'immagine davvero meravigliosa, ottenuta dalla Sonda Voyager 2, durante il suo rapido passaggio accanto all'ultimo Gigante Gassoso del nostro Sistema Solare. Era il 31 Agosto 1989...
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ZB-Neptune_s Partial Rings-PIA02200_modest.jpgNeptune's "Partial Rings" (or "Ring Arcs")76 visiteCaption NASA originale:"One of two new ring arcs, or partial rings, discovered by NASA's Voyager 2 spacecraft, is faintly visible here just outside the orbit of the Neptunian moon 1989N4, also discovered by Voyager 2.
The 155 second exposure taken by Voyager's narrow-angle camera shows the glare of an overexposed Neptune to the right of the moon and ring arc.
The two bright streaks below the moon and ring arc are stars.
The ring arc is approximately 50.000 Km (or 30.000 miles) long".
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Neptune-PIA01539_modest.jpgFarewell Neptune: a "bright smile" for the Earthlings...76 visiteCaption NASA originale:"Voyager 2's post-encounter view of Neptune's South Pole as the spacecraft sped away on a southward trajectory".
E con la Sonda Voyager 2 che sfiorava Nettuno e poi si dirigeva verso i più estremi confini del Sistema Solare - perdendosi per sempre nello spazio interstellare - quest'ultimo frame ci mostra (passateci il termine) il "sorriso" di Nettuno per noi Terrestri.
Un "luminoso sorriso" che a noi piace pensare sia il suo modo di dire "Arrivederci"...
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