Neptune is the eighth planet from the Sun and the fourth largest in diameter. It is smaller in diameter, but bigger in mass than Uranus, with the smallest volume of the four huge planets. Orbit: 4,504,000,000 Km from the Sun; Diameter: 49,532 Km (at equator); Weight: 1.0247 x 1026 Kg. In Roman mythology, Neptune was the god of the seas (Poseidon in Greek mythology).
After Uranus’ discovery, it was observed that the orbit was not in accordance with Newton’s laws. Therefore, it was assumed that the gravitational attraction force of a large nearby spatial object disrupted the orbit of the Uranus. In 1843, English scholar John Couch Adams (1819-1892) suggested, by calculation, that this was due to an unknown planet, far away from the Sun than Uranus. Adams predicted not only the existence of this planet, but also calculated his mass and his orbit, indicating precisely where he was supposed to be. Two years later, French astronomer Urbain Jean Joseph Le Verrier (1811-1877) predicted the place where the new planet lies, between its estimation and that of Adams being a mere one degree difference. Neptune was first observed by Jogann Gottfried Galle and d’Arrest on September 23, 1846, very close to the location established by independent calculations made by Adams and Le Verrier based on observations of the position of the planets Jupiter, Saturn and Uranus. An international dispute between the English and the French (or at least between Adams and Le Verrier) began to prioritize the appointment of the new planet. Today, both are considered the discoverers of Neptune. The following observations have established that the orbits calculated by Adams and Le Verrier differ quite a bit from the current orbit of Neptune. More than two centuries ago, Galileo Galilei noticed the planet Neptune when it was very close to Jupiter, but thought it was a star. He scored in two successive nights as he moved according to the other star. The next night, Galileo did not see her again. If he could have noticed it for a few days, the planet would have been obvious to him. But, unfortunately, the cloudy sky prevented observations for those days and prolonged ignorance for two centuries!
Neptune was overflown by only one spacecraft, ‘Voyager’ 2, on August 25, 1989. Neptune has a revolutionary period of 165 years. The Neptune’s orbit is almost circular: 4.541 million Km maximum sunshine distance, 4.453 million Km distance from the Sun. Due to the eccentricity of Pluto’s orbit, it sometimes intersects the orbit of the planet Neptune, making it for a few years the farthest planet from the Sun. The composition of Neptune is probably similar to that of Uranus, and the two planets are therefore considered pairs of planets. Like Uranus, but different from Jupiter and Saturn, it does not have a distinct internal stratification, with more or less a uniform composition. It has, however, a rocky core, about Earth’s mass, made up largely of iron and silicon. A thick layer of liquid water, ammonia and methane is found around the core. It is surrounded by a gentle gas atmosphere, consisting of approximately 85% hydrogen, 15% helium and methane traces. The planet is 900 times less bright than the Sun. The temperature at the top of the atmosphere above the clouds is very low, about -215 ° C, but 10 ° C warmer than normal. That’s why astronomers believe that like the planets Jupiter and Saturn, Neptune has an internal heat source, emitting twice as much radiation as it receives from the Sun. The dark blue color of Neptune is largely the result of the absorption of red light by methane. In terms of its appearance, Neptune’s upper atmosphere resembles that of Jupiter: there are horizontal clouds of bands, called belts and areas, parallel to the planet’s equator. As a typical gaseous planet, Neptune has strong winds, the fastest in the Solar System, reaching up to 2,000 km / h, concentrated in latitude bands and in devastating great storms. Approximately 50 km above the main cloud cover, although there are white, thin and delicate clouds. Two bright spots of clouds are called Bright Companion and Scooter. The clouds consist of methane that rose to the atmosphere and condensed into ice crystals. The atmosphere of the planet Neptune seems to rotate more slowly than the planet itself, some cloudy formations needing 19 hours to rotate once. The planet rotates around its own axis in 16 hours and 7 minutes. At the time of ‘Voyager’ meeting, Neptune’s most important feature was the Southern Black Sea’s Dark Spot, which was about half the size of the Great Red Peat on Jupiter (about 12,500 Km / 7,500 Km – roughly the Earth’s diameter). similar in appearance and position with it. This was a giant, violent, storm, whirlwind system. The winds shifted the Great Black Spot to the west with 300 m / s. The astronomical observations made in 1994 showed that the Great Dark Spot disappeared! It either broke apart or was covered by other aspects of the atmosphere. A few months later, a new dark spot was observed in the northern hemisphere of Neptune. This indicates that the atmosphere of the planet is changing rapidly, probably due to temperature changes between the base and the top of the clouds. ‘Voyager’ also noticed a smaller spot in the southern hemisphere and an irregular white cloud (“Scooter”). Neptune has rings. It is surrounded by a thin, light and narrow ring system. Terrestrial observations showed only unconfined springs instead of complete rings, but the images on the cosmic ship ‘Voyager 2’ have shown them to be complete with bright areas. Neptune has four rings, consisting of frozen methane particles and carbon compounds. The presence of carbon causes the particles to appear black, so that the rings are almost invisible, very dark, like the rings of Jupiter and Uranus, unlike Saturn’s late rings, which are very bright, reflecting the sunlight. For this reason, the rings of the planet Neptune were discovered relatively recently, in 1984. One of the rings has a twisted structure. Neptune’s rings were named: the outer one is called Adams (which contains three prominent arcs called Liberty, Equality and Fraternity), the next one has no name, the Leverrier ring is still, and the last ring is called Galle. Neptune’s magnetic field is, as Uranus’s, poorly oriented and probably generated by the movement of conductive material (maybe water) in the middle of its layers. For over a century, no other satellite of the planet Neptune has been discovered. In 1949, the Dutch astronomer Gerard Kuiper (1905-1973) discovered the farthest satellite of the planet, which he named after Greek Nimetans, Nereid. The orbit of this satellite has the highest eccentricity of all known satellites of the Solar System: between 1.4 million km and 9.7 million kilometers. The other six satellites were not discovered until 1989 when the Voyager 2 spacecraft flew off the planet Neptune. All are small, dark, orbiting near the surface of the planet Neptune: Naiad, Thalassa, Despina, Galateea, Larissa, Proteus.
The planet Neptune is completely invisible to the naked eye. It can be seen with binoculars, if you know exactly the position, but to see something other than a tiny, pale, low-light disc, you need a powerful telescope.