Neptune was discovered 165 years ago. In that time it has made one complete orbit of the Sun and is now in exactly the same place as when it was discovered all those years ago. The Hubble space telescope has taken anniversary pictures to celebrate this event.
Neptune, as you probably know if you paid attention at school, is the most distant major planet in our solar system. Johann Galle discoveredNeptuneon September 23, 1846. It is 30 times farther away from the Sun than the Earth and its discovery doubled the size of the known solar system. The planet is 2.8 billion miles from the Sun. At this distance there is a very weak pull from the Sun that givesNeptunea large orbit.
Four images of Neptune were taken with the wide Field camera and were taken at four hourly intervals giving a full view of the planet. High altitude clouds can be seen in the northern and southern hemispheres these clouds being composed of methane ice crystals.
Because it is tilted at 29° Neptune experiences seasons just as the Earth does but instead of lasting only a few months such as on Earth each ofNeptune’s seasons continues for about 40 years.
The aqua colour is from the absorption of red light by methane in the atmosphere. The clouds are tinted pink because they are reflecting near-infrared light.
Neptunewas originally found when astronomers found Uranus. Herschel who discovered Uranus noticed that it did not obeyNewton’s theory of gravity. This led to speculation that another planet was tugging on Uranus altering its motion. Astronomers then found Uranus.
If you’re looking forNeptuneit cannot be seen by the naked eye. It can be seen though by binoculars or a small telescope in the constellation Aquarius close to the boundary with Capricorn.
It seems that Neptune like mass planets orbiting other stars may be common in our Milky Way galaxy. The Kepler mission has found increasingly smaller extrasolar planets with many the size of Neptune.