5th June: Neptune

John Couch Adams, English mathematician and astronomer who used mathematics to predict the orbit of the planet Neptune, was born on this date in 1819. Here are ten facts about his famous discovery.

1. Neptune's mass is 1.0243×1026 kg, 17 times that of Earth. It is the fourth-largest planet in the solar system and the farthest from the sun since Pluto was demoted.
2. It can't be seen with the naked eye from Earth and was therefore the first to be discovered using mathematics and observing its effect on its neighbour, Uranus. In 1821, Alexis Bouvard published astronomical tables of the orbit of Uranus, but he then found substantial deviations from his tables, and hypothesised that something else was out there, exerting its gravitational force on Uranus. In the 1840s, both John Couch Adams and a French astronomer, Urbain Le Verrier worked out the orbit of the new planet mathematically but at first nobody was very interested. Eventually, Adams persuaded Cambridge Observatory director James Challis to look for it with a telescope but he didn't find anything. Meanwhile, Le Verrier wrote to Berlin Observatory astronomer Johann Gottfried Galle persuading him to try. He received the letter on 23 September 1846, and that very evening got his telescope out and found Neptune, pretty much exactly where Le Verrier said it would be.
3. This led to some argument between England and France over who should get the credit for the discovery. At the time, it was decided they should share the credit, but following a review of the documents the "Neptune papers" the verdict was that Le Verrier should get most of the credit.
4. It was Le Verrier who suggested the name Neptune (the Roman god of the sea) for the planet then known as "the planet exterior to Uranus". Other suggestions were Janus (from Galle) and Oceanus (from Challis). For a while, Le Verrier proposed naming the planet after himself, but nobody outside France was keen on this idea. Neptune is so called in most languages, and in the languages which call it by a different name, the sea god theme is maintained. In Chinese, Japanese, and Korean, the planet's name was translated as "sea king star"; In Mongolian, Neptune is called Dalain Van after the Mongolian ruler of the sea; In modern Greek the planet is called Poseidon, the Greek counterpart of Neptune. In Māori, it is Tangaroa, the Māori god of the sea; in Nahuatl, it's Tlāloccītlalli, after the rain god Tlāloc. In Hebrew, it's called Rahab, after a sea monster mentioned in the Bible.
5. Neptune has rings, although they are less obvious than Saturn's. The rings look slightly red and so it's thought they are made of ice particles coated with silicates or carbon-based material. Le Verrier may not have managed to get the planet named after him, but one of the rings bears his name. Other rings are named for Galle and Adams.
6. Neptune takes 164.8 years to orbit the Sun.
7. Neptune has 14 moons - that we know about. A new moon was discovered in 2013. It doesn't have a name yet; it's currently referred to as S/2004 N 1, but names are being considered and it will likely be named after a minor sea god like the other moons. The largest, and first to be discovered is Triton. Triton was discovered by William Lassell (who also has a part of the planet's ring system named after him) 17 days after the discovery of Neptune itself. Triton accounts for over 99% of the mass in orbit around the planet and is the only moon of Neptune big enough to be a sphere. The other moons include Nereid, Proteus, Naiad, Thalassa, Despina, Galatea and Larissa.
8. The core of Neptune is composed of Iron, nickel and silicates. The upper atmosphere is 80% hydrogen and 19% Helium with a trace amount of methane. Increasing concentrations of methane, ammonia and Water are found in the lower atmosphere.
9. Winds on Neptune travel at almost 600 m/s (2,200 km/h; 1,300 mph), twice the speed of a high speed jet.
10. Its astronomical symbol is ♆, a stylised version of Neptune's trident. It is the ruling planet of Pisces and of Friday, and associated in astrology with sensitivity, idealism and compassion, illusion, confusion, and deception. Neptune governs hospitals, prisons, mental institutions, and any other place, such as a monastery, where people might go to retreat from society. In astrological medicine, it rules the thalamus, the spinal canal, and severe or mysterious illnesses and neuroses. Its appearance in the sky is linked by astrologers with historical events such as the discovery of anaesthetics and hypnotism; the rise of nationalist movements seeking independence in countries throughout Europe; the rise of socialism, the beginnings of the welfare state and the publication of Marx and Engels' 'The Communist Manifesto' in 1848.