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From Citizendium, the Citizens' Compendium
Neptune is the first planet predicted through indirect observation and mathematical deduction, although Galileo did record it as a fixed star in 1612 and 1613. Aberrations in the orbit of Uranus led French mathematician and astronomer Urbain Joseph Le Verrier to propose influence by an unknown planet whose mass and position would effect it. His proposals were ignored until Johann Gottfried Galle at the Berlin Observatory found Neptune the first night he began searching for it in 1846.
Parameters for classification as a planet
Neptune is classified as a planet by the International Astronomical Union for meeting the following criteria:
- Orbits the Sun;
- Has mass sufficient for its gravity to form a nearly round shape;
- Has mass sufficient for gravity to clear a path in its orbit.
Neptune is approximately 30 times as far from the Sun as Earth (30 AU). Though slightly smaller than Uranus, it is more dense and is about seventeen times more massive than Earth (17 Earth masses). At its distance from the Sun, it receives about one thousandth of the same sunlight as Earth. It radiates more internal heat than it receives from the Sun, though less than Jupiter or Saturn, indicating a radioactive inner core.
The average temperature on Neptune is -200° C (-392° F). Recent measurements have shown the southern pole to be about 10° C hotter than the planet's average. This results in the vaporisation of the frozen methane and its circulation to the upper layers of the atmosphere. Neptune is comprised predominantly of hydrogen and helium. However, its methane component reaches the upper atmosphere absorbing red light from sunlight and reflects the blue spectrum making Neptune appear blue.
Neptune’s polar orientation is similar to Earth’s with the northern pole tilting toward or away from the Sun in season. The northern hemisphere summers and winters lasts approximately 40 years each. The variation in polar tilts and increased temperature may be a contributing factor to the winds on Neptune which reach velocities of about 2,000 k/h (1,240 m/h)
Neptune has an orbital period (sidereal year) of 164.79 earth years. At is closest approach to the Sun (perihelion) it is nearly 30 times the distance of the Earth from the Sun (29.80 AU). At its furthest distance from the Sun (aphelion) it is 30.32 AU from the Sun.
Natural satellitesNeptune has thirteen moons. The largest, Triton, is geologically active, with geysers of liquid nitrogen. retrograde orbit. Neptune possesses a number of Trojan asteroids.
- ↑ 1.0 1.1 1.2 1.3 Neptune NASA
- ↑ 2.8 billion miles
- ↑ Honey, I Shrunk the Solar System NASA. “The International Astronomical Union has decided that, to be called a planet, an object must have three traits. It must orbit the Sun, be massive enough that its own gravity pulls it into a nearly round shape, and be dominant enough to clear away objects in its neighborhood.”
- ↑ 4.0 4.1 4.2 A warm south pole on Neptune NASA 18/09/07. Retrieved 4/11/07
- ↑ Podolak, M.; Reynolds, R. T.; Young, R. (1990). Post Voyager comparisons of the interiors of Uranus and Neptune. NASA, Ames Research Center. Retrieved on 2006-01-16.
- ↑ Methane red-light absorption and blue-green reflection also gives Uranus (planet) its blue-green colour
- ↑ The orbits of the planets National Maritime Museum
- ↑ Duxbury, N.S., Brown, R.H. (1995). The Plausibility of Boiling Geysers on Triton. Beacon eSpace. Retrieved on 2006-01-16.
- ↑ Triton