The rings around the planet Uranus may have been spotted nearly 190 years prior to the accepted date for their discovery, according to a theory.
According to the orthodox view, the rings around Uranus were detected during an experiment in 1977.
Now, a scientist has re-evaluated a claim made in 1797 by astronomer Sir William Herschel that he saw rings around the seventh planet.
The claim had previously been dismissed as a mistake.
The new idea was presented at the Royal Astronomical Society's National Astronomy Meeting in Preston, UK.
Dr Stuart Eves, who works for Surrey Satellite Technology Limited, first came up the idea when he was given a framed page from an encyclopaedia published in 1815 for his birthday.
The page shows an orrery - a mechanical device detailing the relative positions and motions of planets and moons.
Made by the craftsman William Pearson, it showed the planet Uranus, with its spin axis in the correct plane, with six smaller objects spinning around it.
It was unlikely that these objects were moons. Although two Uranus satellites were found the 18th Century, the sixth moon of Uranus was not found until 1985, after Nasa's Voyager probe flew past the planet.
After researching the subject, Dr Eves found that the Pearson orrery in the encyclopaedia page was based on observations made by Sir William Herschel, who discovered the seventh planet in 1781.
'A ring suspected'
When Dr Eves tracked down Herschel's notes detailing his observations of Uranus, he found the following passage: "February 22, 1789: A ring was suspected".
Herschel even drew a small diagram of the ring and noted that it was "a little inclined to the red". The Keck Telescope in Hawaii has since confirmed this to be the case. Herschel's notes were published in a Royal Society journal in 1797.
Dr Eves told BBC News: "I was thinking, 'could he have got all of that right'? He has one ring, rather than multiple rings as there are at Saturn; it is relatively close to the planet and it's about the right size.
"The opening angle is about right. Astronomical software indicates that it may have been slightly more open as viewed from Earth on the dates Herschel was observing," he added.
"But there are reasons for thinking that the ring plane moves about a bit, and he has the major axis of the ring plane in the right direction. I started to add up all the statistics and I said: I reckon he had a point.
"[Herschel] is not just superimposing a saturnian-style ring system on Uranus. I think it is compelling from a psychological point of view, because he really didn't have much to compare it with at the time."
Other astronomers have dismissed the possibility that Herschel discovered rings around Uranus. They claim that it would have been far too faint for him to have seen from the ground, using contemporary telescopes.
Clear skies
The ring was officially discovered in 1977 during an occultation experiment. One question some will be asking is why no one saw the ring in the intervening years.
Stuart Eves thinks there may be a few reasons for this. Firstly, there are only a few windows of opportunity during which the rings present themselves to Earth.
The Cassini-Huygens mission has also observed darkening of the rings of Saturn. This may be due to dust accumulating on the icy material in the rings.
If this process is happening on Saturn, Dr Eves argues, it could be happening on Uranus. The seventh planet's rings may have been brighter in 1787, allowing Herschel to spot them from Earth. Several other effects could also cause variability in the rings, including loss of material from them.
Another factor may lie with the Earth's atmosphere. As the industrial revolution proceeded apace, light pollution and smog may have prevented subsequent observers from seeing the planet's rings.
More speculatively, a cold snap called the Maunder Minimum, which lasted from 1645 to 1715 and saw temperatures that were on average five degrees lower than today, might have removed water vapour from the atmosphere, locking it up as ice.
If the climate was still relatively cold by the time Herschel made his observations, less water vapour may have made skies clearer and therefore more suitable for astronomy.
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Comment: As for Sir William Herschel - from this link. Also drop 'Planet X' or 'The 12th Planet' and add 'Dark Companion Brown Dwarf Star' on the linked website and you see a picture that has been hidden from us start to form.
New York Times
January 30, 1983
Something out there beyond the farthest reaches of the known solar system seems to be tugging at Uranus and Neptune. Some gravitational force keeps perturbing the two giant planets, causing irregularities in their orbits. The force suggests a presence far away and unseen, a large object that may be the long- sought Planet X. ... The last time a serious search of the skies was made it led to the discovery in 1930 of Pluto, the ninth planet. But the story begins more than a century before that, after the discovery of Uranus in 1781 by the English astronomer and musician William Herschel. Until then, the planetary system seemed to end with Saturn.
As astronomers observed Uranus, noting irregularities in its orbital path, many speculated that they were witnessing the gravitational pull of an unknown planet. So began the first planetary search based on astronomers predictions, which ended in the 1840's with the discovery of Neptune almost simultaneously by English, French, and German astronomers. But Neptune was not massive enough to account entirely for the orbital behavior of Uranus. Indeed, Neptune itself seemed to be affected by a still more remote planet. In the last 19th century, two American astronomers, Willian H. Pickering and Percival Lowell, predicted the size and approximate location of the trans-Neptunian body, which Lowell called Planet X. Years later, Pluto was detected by Clyde W. Tombaugh working at Lowell Observatory in Arizona. Several astronomers, however, suspected it might not be the Planet X of prediction. Subsequent observation proved them right. Pluto was too small to change the orbits of Uranus and Neptune, the combined mass of Pluto and its recently discovered satellite, Charon, is only 1/5 that of Earth's moon.
Recent calculations by the United States Naval Observatory have confirmed the orbital perturbation exhibited by Uranus and Neptune, which Dr. Thomas C Van Flandern, an astronomer at the observatory, says could be explained by "a single undiscovered planet". He and a colleague, Dr. Richard Harrington, calculate that the 10th planet should be two to five times more massive than Earth and have a highly elliptical orbit that takes it some 5 billion miles beyond that of Pluto - hardly next-door but still within the gravitational influence of the Sun. ...