Neptune, the outermost planet, was discovered on 23 September 1846. Along its vast orbit, Neptune slowly orbits the Sun every 60,190 Earth days, nearly 165 Earth years. This means that on 11 July 2011 Neptune completed its first full orbit, since its discovery. Celebrating this rare anniversary, NASA’s Hubble Space Telescope (HST), exploring the universe from Earth orbit, acquired interesting images of Neptune, in June 2011.
Five planets, Mercury, Venus, Mars, Jupiter and Saturn, have been known since prehistoric times, since they are visible to the unaided eye. However, Neptune cannot be viewed with the naked eye, as it is distant and faint. The discovery of Neptune is regarded a scientific triumph, since the planet’s position in the sky was predicted mathematically, leading to direct discovery, through the telescope.
Unexpected irregularities in the orbit of Uranus, the seventh planet, led the French astronomer Alexis Bouvard (1767-1843) to postulate that its orbit was disturbed by the gravity of an unknown planet. In the summer of 1846, another French astronomer, Urbain Le Verrier (1811-1877), studied the motion of Uranus, and was able, through mathematical computations, to precisely find the location of the eighth planet.
Neptune was discovered at the Berlin Observatory, due to an alert from Le Verrier, very close to the position predicted by Le Verrier. Interestingly, Galileo Galilei (1564-1642), the scientist who developed the telescope, and applied it to astronomical observations, was the first to record Neptune, in 1612, but he mistook it for a star!
Neptune (approximately 49,000 km across) is a giant planet, whose diameter is about four times that of Earth. It is located approximately 4,500 million km from the Sun, about 30 times the average Earth-Sun distance. It has 13 moons and delicate faint rings. It rotates rapidly about its axis, every 16 hours.
Neptune’s characteristic blue color is due to methane gas, present in the planet’s dense, turbulent atmosphere. In Neptune, wind speeds reach up to 2,000 km/h. Due to its remoteness from our planet, even with powerful telescopes such as HST, Neptune only appears as a small disk, showing some detail, attributed to Neptunian atmospheric phenomena.
However, in 1989, NASA’s Voyager 2 spacecraft flew by Neptune, and approached it to within only 5,000 km. It relayed detailed images of Neptune and its moons.
References
Hubble Site
http://hubblesite.org/
NASA
www.nasa.gov/
The European Space Agency’s Hubble Website
Wikipedia