Voyager 2 Image of Neptune
Voyager 2 Image of Neptune
One of the most controversial episodes in the history of British science will be the subject of the next National Astronomy Week, at the end of September 1996. It concerns the failure of British astronomers to discover the planet Neptune 150 years ago, despite the existence of calculations that predicted its existence.
In 1781, the planet Uranus had been discovered telescopically from Britain by William Herschel. It was the first planet not known since ancient times, because it is too faint to be noticed with the naked eye, and its discovery doubled the size of the known Solar System overnight. Herschel received Royal patronage for his sensational discovery and built the biggest and best telescopes in the world, with which he and his son John surveyed the northern and southern skies.
Earlier, Isaac Newton's theory of gravitation, and Edmond Halley's use of it to predict the return of the comet that now bears his name, had explained the physics of the heavens. Against this background, it seemed that Britain had established proprietorial rights over celestial discoveries.
Thus in 1845, a Cambridge mathematician, John Couch Adams, predicted the existence of an unseen planet, to account for the fact that Uranus was being pulled slightly out of position in its orbit. Adams attributed this pull to the gravitational effect of an unknown body, and calculated its position.
Adams visited the Royal Observatory at Greenwich to present his findings to the Astronomer Royal, Sir George Airy, the top scientific civil servant of his day. But Airy was unavailable and although Adams left a note of his calculations Airy at first took little interest, believing that the Royal Observatory should not be diverted from its publicly funded work on timekeeping and navigation, in which it was world leader, to search for new planets.
Only when a French mathematician, Urbain Leverrier, published a similar prediction to Adams did Airy take action. He asked Professor James Challis at Cambridge University to begin a search. Challis began in July 1846 and actually sighted the new planet four times without recognising it. Meanwhile, Leverrier had enlisted the help of astronomers at Berlin Observatory, who found the new planet on the night of 23 September 1846.
Inevitably, Airy and Challis found themselves at the centre of a national scandal once it was realised that they had let the French and Germans beat them to the discovery. The controversy is bound to be re-examined on the 150th anniversary in 1996.
A detailed account of the Neptune affair can be found in 'The Planet Neptune' by Patrick Moore (John Wiley, Chichester, 1988).
A new book - 'The Neptune File': Planet Detectives and the Discovery of Worlds Unseen. by Tom Standage has new information that was lost until 1999.
| Neptune | |
|---|---|
| Diameter at equator | 49.530 km |
| Average distance from the Sun | 4,497 million km |
| Time to orbit Sun | 164.8 years |
| Rotation period | 16h 07m |
| Axial inclination | 28.3deg |
| Mass | 17.2 x Earth |
| Volume | 54 x Earth |
| Density | 1.76 |
| Escape velocity | 24.6 km/s |
| Known moons | 8 |
| Moons of Neptune | ||||
|---|---|---|---|---|
| Moon | Diameter (km) | Orbital Radius (km) | Orbital Period (days) | Year Discovered |
| Naiad | 60 | 48,200 | 0.29 | 1989 |
| Thalassa | 80 | 50,000 | 0.31 | 1989 |
| Despina | 148 | 52,500 | 0.33 | 1989 |
| Galatea | 158 | 62,000 | 0.43 | 1989 |
| Larissa | ~190 | 73,600 | 0.55 | 1989 |
| Proteus | ~415 | 117,000 | 1.12 | 1989 |
| Triton | 2,706 | 354,800 | 5.88 | 1846 |
| Nereid | 340 | 5,513,000 | 360.1 | 1949 |
| Rings of Neptune | ||
|---|---|---|
| Ring name | Distance from centre (km) | Width km |
| Galle | 41,900-43,600 | 1,700 |
| Leverrier | 53,200 | 15 |
| Plateau | 53,200-59,100 | 5,900 |
| Adams | 62,900 | 50 |
Where did the Neptune
papers go?.
Adams,
Airy and the Discovery of Neptune in 1846. by Allan Chapman.
William Lassell
and the Triton discovery.
The
Nine Planets (Neptune). (SEDS)
Voyager
Project Home Page (Neptune images).
