| Mean distance from the Sun | 4496.7 millions Km (2795 millions of miles) |
| Revolution period | 164.8 years |
| Rotational period | 17h52m |
| Diameter | 49,500 Km - 30760 miles (equatorial) |
| Mass (Earth=1) | 17.2 |
| Volume (Earth=1) | 57 |
| Gravity (Earth=1) | 1.2 |
| Number of satellites | 8 |
| Mean temperature | -220 °C |
| Minimum distance from the Earth | about 4,350 millions Km (2700 millions of miles) |
| Maximum distance from the Earth | about 4,650 millions Km (2890 millions of miles) |
Generalities:
it is the last of the great gaseous planets. Besides being the farthest
planet from the Sun it is also the smallest of the family of the gaseous
planets. Its dimensions are nevertheless similar to Uranus’ones, while
its density is slightly superior. Its atmospheric composition shows, together
with hydrogen and helium, a fraction of other mixtures, mainly water, methane
and ammonia, in a more marked way in comparison to Uranus. Because of its
composition, and mainly because of the presence of methane, the coloration
of its atmosphere appears of blue color. Neptune shows a rather turbulent
atmosphere, with high speed currents and whirling formations as the
clearest cloud recorded by Voyager probes and showing similarities with
the Great Red Cloud of Jupiter. Even Neptune, like the other gaseous planets,
shows an inside energetic source. The probes that have visited it have
recorded extremely weak rings.
Observation:
Neptune is completely invisible with a naked eye in the terrestrial sky,
being next to the eighth magnitude. It can be observed with a telescope
of small power or with simple binoculars as well. The greatest
difficulty lies in the fact that it is necessary to distinguish it from
the numerous stars of similar brightness present in its outskirts. For
this reason it is necessary to be provided of a stellar map and to know
its precise position. If you have some doubts, it is possible to repeat
the observation in a few days and to notice Neptune as the only star to
have moved in comparison to the others. Being invisible with a naked eye,
it was discovered only last century, in 1846, founding the observations
on the mathematical calculations operated by the astronomer Le Verrier,
who had noticed the gravitational perturbations suffered by Uranus from
a still unknown body.
Having
an extremely slow motion among the stars, it practically goes to opposition
every 12 months, and can be observed for long periods
Satellites:
Neptune’s satellites that can be observed from the Earth are two: Triton
and Nereide. The former has great dimensions, esteemed to be about 6,000
Km, while the latter has dimensions clearly inferior to 500 Km and has
a very eccentric orbit around the planet. The other satellites are very
small and all of them were discovered by Voyager in 1989.
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Visibility
of planets during this month
