| Piú votate - SOLAR SYSTEM |
The Rings-2-PIA07872.jpgThe "Rings": the most spectacular view ever seen!66 visiteSpecially designed Cassini orbits place Earth and Cassini on opposite sides of Saturn's rings, a geometry known as "occultation". Cassini conducted the 1st radio occultation observation of Saturn's Rings on May 3, 2005.
Three simultaneous radio signals of 0,94; 3,6, and 13 cm wavelengths (Ka-, X-, and S-bands) were sent from Cassini through the rings to Earth. The observed change of each signal as Cassini moved behind the Rings provided a profile of the distribution of ring material as a function of distance from Saturn, or an optical depth profile.
This simulated image was constructed from the measured optical depth profiles. It depicts the observed ring structure at about 10 Km in resolution. Color is used to represent information about ring particle sizes in different regions based on the measured effects of the 3 radio signals. Shades of purple, primarily over most of the inner ring (ring B) and the inner portion of the next ring (ring A), indicate regions where there is a lack of particles less than 5 centimeters (about 2 inches) in diameter. Green and blue shades indicate regions where there are particles of sizes smaller than 5 centimeters (2 inches) and 1 centimeter (less than one third of an inch), respectively, primarily in outer ring A and within most of ring C. From other evidence in the radio observations, all ring regions appear to be populated by a broad range of particle size distribution that extends to boulder sizes (several to many meters or yards across). 
(11 voti)
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ZZ-ZZ-HybridEclypse-Heinsius_Panama_tse2005_1.jpgAn unusual "Hybrid Solar Eclipse" (2)71 visiteDa "NASA - Picture of the Day" del 6 Maggio 2005:"(...) But for Stephan Heinsius, near the end of the shadow track at Penonome Airfield, Panama, the Moon's apparent size had shrunk enough to create an anular eclipse, showing a complete anulus of the Sun's bright disk as a dramatic "Ring of Fire".
(...) How rare is such a Hybrid Eclipse?
Calculations show that during the 21st century just 3,1% (7 out of 224) of Solar Eclipses are hybrid while hybrids comprise about 5% of all Solar Eclipses over the period from 2.000 BC to AD 4.000".
(11 voti)
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Venusian_Clouds-IR-PIA00124.jpgLow altitude Venusian clouds (false colors)103 visiteThis false-color image is a near-infrared map of lower-level clouds on the night side of Venus, obtained by the Near Infrared Mapping Spectrometer aboard the Galileo spacecraft as it approached the planet's night side on February 10, 1990. Bright slivers of sunlit high clouds are visible above and below the dark, glowing hemisphere. The spacecraft is about 100.000 Km above the planet. An infrared wavelength of 2,3 microns (about 3 times the longest wavelength visible to the human eye) was used. The map shows the turbulent, cloudy middle atmosphere some 50-55 Km above the surface, 10-16 Km below the visible cloudtops. The red color represents the radiant heat from the lower atmosphere (about 400° Fahrenheit) shining through the sulfuric acid clouds, which appear as much as 10 times darker than the bright gaps between clouds. This cloud layer is at about -30° Fahrenheit, at a pressure about 1/2 Earth's surface atmospheric pressure. Near the equator, the clouds appear fluffy and blocky; farther north, they are stretched out into East-West filaments by winds estimated at more than 150 mph, while the poles are capped by thick clouds at this altitude.
(11 voti)
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Mathilde-PIA02479.jpgMathilde80 visiteCaption NASA originale:"Two different views of asteroid 253 Mathilde were obtained by the NEAR spacecraft on June 27, 1997. The image at left was obtained as the spacecraft approached Mathilde with its camera pointed near the direction of the Sun; only a few of the prominent ridges on Mathilde are illuminated. The visible area at left is 29 Km (approx. 18 miles) high and the phase angle (the angle from Sun-Mathilde spacecraft) is 136°. As the spacecraft receded from Mathilde, it observed the asteroid (about 60 Km - or 38 miles across) almost fully lit by the Sun at a phase angle of 43° (right image). Mathilde's irregular shape results from a long history of severe collisions with smaller asteroids. The largest visible crater is about 30 Km (19 miles) in diameter".
(11 voti)
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Mathilde-PIA02494.jpgMathilde and Eros: C-Type and S-Type71 visiteCaption NASA originale:"In this montage, Mathilde (at left) and Eros (at right) are shown at the same scale, as they were imaged by NEAR Shoemaker from about 1.800 Km on June 27, 1997, and February 12, 2000, respectively. Mathilde is 56 Km across and Eros is 33 Km long and 13 Km wide. However, Mathilde's brightness is greatly exaggerated for viewing purposes - it's actually 6 times darker than Eros, with about the same reflectivity as soot! In a scheme that reflects how asteroids have historically been a topic for astronomy, not geology, they are classified into groups based on their colors as observed through telescopes. The 2 major classes of asteroids are called S-Types and C-Types. S-Types, whose colors are consistent with "stony" or rocky compositions, prevail among asteroids that orbit closer to the Sun than the mid-point of the asteroid belt. Eros and the 2 asteroids encountered briefly by the Galileo spacecraft on its way to Jupiter - Gaspra and Ida - are all S-Types. C-Types like Mathilde have a dark gray color consistent with a "carbonaceous" composition, rich in carbon compounds and other dark materials. They prevail in the outer part of the asteroid belt".
(11 voti)
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Neq-Neptune-PIA00051.jpgNeptune in false colors65 visiteCaption NASA originale:"In this false color image of Neptune, objects that are deep in the atmosphere are blue, while those at higher altitudes are white. The image was taken by Voyager 2's wide-angle camera through an orange filter and two different methane filters. Light at methane wavelengths is mostly absorbed in the deeper atmosphere. The bright, white feature is a high altitude cloud just south of the Great Dark Spot. The hard, sharp inner boundary within the bright cloud is an artifact of computer processing on Earth. Other, smaller clouds associated with the Great Dark Spot are white or pink, and are also at high altitudes. Neptune's limb looks reddish because Voyager 2 is viewing it tangentially, and the sunlight is scattered back to space before it can be absorbed by the methane. A long, narrow band of high altitude clouds near the top of the image is located at 25° north latitude and faint hazes mark the equator and polar regions".
(11 voti)
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Miranda-PIA00140.jpgMiranda, from approx. 31.000 Km110 visiteCaption NASA originale:"This Voyager 2 image of Miranda was taken Jan 24, 1986, from a distance of about 31.000 Km (19.000 miles), shortly before the spacecraft's closest approach to the Uranian moon. The HR of 600 meters (2.000 feet) reveals a bewildering variety of fractures, grooves and craters, as well as features of different albedos (reflectancea). This clear-filter, narrow-angle view encompasses areas of older, heavily cratered terrain with a wide variety of forms. The grooves and troughs reach depths of a few Km (or miles) and expose materials of different albedos. The great variety of directions of fractures and troughs, and the different densities of impact craters on them, signify a long, complex geologic evolution of this satellite".
(11 voti)
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The Solar Spectrum_noao.jpgThe Solar Spectrum and the "missing colors"...66 visiteDa "NASA - Picture of the Day" del 27 Febbraio 2005:"It is still not known why the Sun's light is missing some colors. Shown above are all the visible colors of the Sun, produced by passing the Sun's light through a prism-like device. The above spectrum was created at the McMath-Pierce Solar Observatory and shows, first off, that although our yellow-appearing Sun emits light of nearly every color, it does indeed appear brightest in yellow-green light. The dark patches in the above spectrum arise from gas at or above the Sun's surface absorbing sunlight emitted below. Since different types of gas absorb different colors of light, it is possible to determine what gasses compose the Sun. Helium, for example, was first discovered in 1870 on a solar spectrum and only later found here on Earth. Today, the majority of spectral absorption lines have been identified - but not all".
(11 voti)
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Saturn-W00003808.jpgSaturn and Dione88 visitenessun commento
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A - Uranus.jpgUranus from Voyager 2109 visiteUranus Data and Statistics
Discovered by William Herschel
Date of discovery = AD 1781
Mass (kg) = 8.686e+25
Mass (Earth = 1) = 1,4535e+01
Equatorial radius = 25.559 Km
Equatorial radius (Earth = 1) = 4,0074
Mean density (gm/cm^3) = 1,29
Mean distance from the Sun = 2.870.990.000 Km
Mean distance from the Sun (Earth = 1) = 19,1914
Rotational period (hours) = - 17,9
Orbital period (years) = 84,01
Mean orbital velocity = 6,81 Km per second
Tilt of axis = 97,86°
Orbital inclination = 0,774°
Equatorial surface gravity (m/sec^2) = 7,77
Equatorial escape velocity = 21,30 Km per second
Magnitude (Vo) = 5,52
Mean cloud temperature = - 193°C
Atmospheric pressure (bars) = 1,2
Atmospheric composition: Hydrogen 83%; Helium 15%; Methane 2%
(11 voti)
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Japetus-PIA06145_modest.jpgSharp views of Japetus67 visiteIn sequenza, alcune delle migliori immagini di Giapeto ottenute da Cassini e superiori, per qualità e dettaglio, a quelle ottenute dalla Sonda Voyager 2 qualche anno fa. Le immagini a colori visibili sulla Sn dell'Osservatore ed al centro sono state ottenute usando (e combinando) i filtri per l'ultravioletto (a 338 Nnmts), il verde (a 568 Nnmts) e l'infrarosso (a 930 Nnmts); l'immagine a Dx è stata ottenuta riprendendo nel cosiddetto "spettro visibile". Le immagini sono state riprese da una distanza oscillante fra gli 1,1 e gli 1,3 MKMs; Giapeto si caratterizza sia per il gigantesco cratere da impatto visibile nell'emisfero sud (400 Km di diametro), sia per alcune notevoli differenze di albedo fra diverse zone della sua superficie (il che ci fa supporre che esistano aree ricoperte, probabilmente, da vasti depositi di polveri - che sono causa di una bassa riflessione della luce ergo di una bassa albedo - ed altre aree che, forse, sono costituite da rocce o addirittura da depositi di ghiaccio).
(11 voti)
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Tethys-PIA06140-N-HD.jpgTethys in natural colors (HD)70 visiteCommento NASA originale estratto da "NASA - Picture of the Day" del 29 Novembre 2004:"Tethys is one of the larger and closer moons of Saturn. The Cassini spacecraft now orbiting Saturn passed near the frozen moon at the end of October, capturing the most detailed images since the Voyager spacecrafts in the early 1980s. Tethys is composed almost completely of water ice and shows a large impact crater that nearly circles the planet. Because this crater did not disrupt the moon, Tethys is hypothesized to be at least partly liquid in its past. Two smaller moons, Telesto and Calypso, orbit Saturn just ahead of and behind Tethys. Giovanni Cassini discovered Tethys in 1684. The Cassini spacecraft is scheduled for a close fly-by of Tethys in September 2005".
(11 voti)
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