Astronomy Picture of the Day
August 25, 2012

Farewell to Neptune
Farewell to Neptune

Credits: NASA - Voyager 2 Project; Credits fo the additional process. and color.: Dr Paolo C. Fienga/LXTT/IPF

Neptune is the 8th (eighth) Planet from the Sun in the Solar System, the 4th (fourth) largest Planet by diameter, and the third (still largest) Planet by Mass (consider that Neptune is about 17 times the Mass of Earth and is somewhat more massive than its near-twin Uranus, which is approx. 15 times the Mass of Earth but not as dense). On average, Neptune orbits the Sun at a distance of 30,1 Astronomical Unit, such as, approximately, 30 times the EarthSun distance. Named after the Roman God of the Seas, its astronomical symbol is "♆": a stylized version of the God Neptune's Trident.

Neptune was the 1st (first) Planet found by way of Mathematical Prediction rather than "empirical observation". In fact, some unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce that its orbit was subject to Gravitational Perturbation by an (at the time) Unknown Planet. Neptune was subsequently observed on September 23, of the AD 1846, by Johann Galle within a degree of the position predicted by Urbain Le Verrier, and its largest moon, Triton, was discovered shortly thereafter (even though none of Neptune's remaining moons was telescopically located until the 20th Century). Neptune has been visited by only one Spacecraft, such as the NASA - Voyager 2 Space Probe, which flew by this Icy Gas-Giant Planet on August, 25, 1989.

Neptune is similar in composition to Uranus, and both have compositions which differ from those of the other two larger Gas-Giant Planets, Jupiter and Saturn. The Atmosphere of Neptune, like the one of Jupiter and Saturn, is primarily composed of Hydrogen and Helium, along with traces of Hydrocarbons and possibly Nitrogen, but it also contains a way higher proportion of "Ices" (---> Ice Particles) such as Water, Ammonia and Methane. However, the interior of Neptune, just like Uranus' one, is primarily composed of Ices and Rock; furthermore, distinct traces of Methane in the Outermost Regions of its Atmosphere, are to be considered in order to explain the Planet's blueish appearance.

In contrast to the relatively featureless Atmosphere of Uranus, Neptune's Atmosphere is notable for its active and visible Weather Patterns. For example, at the time of the 1989 NASA - Voyager 2 Space Probe Fly-By, the Planet's Southern Hemisphere showed a Great Dark Spot that is actually comparable to the Great Red Spot on Jupiter. These Weather Patterns are driven by the strongest Winds of any Planet in the Solar System, with recorded Wind Speeds as high as about 2100 Km-per-hour (such as approx. 1300 mph). Because of its great distance from the Sun, Neptune's Outer Atmosphere is one of the coldest places in the Solar System, with temperatures - measured at the Top of its Clouds - approaching (minus) 218° Celsius (such as 55 K); on the other hand, the estimated temperatures existing near the Planet's core should be of approximately 5400 K (such as about 5000° Celsius). Neptune also possesses a faint and highly fragmented Ring System (which is actually made up of Features known as "Ring Arcs") which, even though it may have been detected during the 1960s, was indisputably confirmed in the AD 1989, by the NASA - Voyager 2 Space Probe.

This frame has been additionally processed and then re-colorized, according to an informed speculation carried out by Dr Paolo C. Fienga (LXTT-IPF), in Absolute Natural Colors (such as the colors that a human eye would actually perceive if someone were onboard the NASA - Voyager 2 Probe and then looked outside, towards the Planet Neptune and its moon Triton), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. Different colors, as well as different shades of the same color, mean, among others, the existence of different Elements in the Upper Atmosphere of Neptune, each having a different Albedo (---> Reflectivity) and Chemical Composition.

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