That tiny black dot in Galileo's notes...

Last Updated : 27 July 2009, 12:16 IST
Last Updated : 27 July 2009, 12:16 IST

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In another three months, physicists at Florence will start analysing the antiquity of a tiny dot inscribed on a parchment four hundred years ago with the ambitious aim of determining once and for all whether Galileo Galilei first discovered planet Neptune 238 years before its official discovery by Urbain Leverrier.

 Neptune was the first planet, discovered purely on the merit of scientific calculations. Though the credit goes to Leverrier, same calculations were made independently in England by John Admas.

 While studying the Uranus orbit, both were perturbed by an unidentified source of gravitational influence after allowances were made on the gravitational pull by other planetary bodies. This led to the prediction about the presence of another planet circling the sun.

 After Leverrier published his observations showing the deviation in Uranus’ orbit, the Cambridge Observatory scoured the night sky in August and September of 1846. Meanwhile, Leverrier approached the Berlin Observatory on September 23, 1846, requesting the observatory to look for the unseen planet.

 Call it serendipity, but on the day of receiving the Leverrier letter, Neptune was discovered within one degree of the location predicted by Leverrier and within 12 degrees of the place suggested by Adams.

 James Challis, then director of the Cambridge Observatory later realised he saw the planet twice in August but failed to recognise it.

And the credit goes to...
The discovery triggered one more England-France rivalry on who should be given the credit. Eventually both were credited. But now an Australian physicist claims it is Galileo who first observed Neptune way back in the 17th century. Notes from Galileo’s observations reveal he unwittingly observed Neptune 234 years before its official discovery, said David Jamieson from the University of Melbourne, who claims to have unearthed new evidences to back up his claim. The evidences come from the scrutiny of voluminous Galileo notebooks kept in the archives of the University of Florence.
Previous analysis of Galileo drawings show he did observe Neptune but mistook it for a fixed star when it appeared very close to Jupiter in the night sky. That’s the reason Neptune’s discovery is not ascribed to Galileo.
Jamieson claimed on the night of January 28 in 1613 that Galileo noted that the “star (Neptune) appeared to have moved relative to an actual nearby star,” – an indirect proof of the planetary motion.

A mysterious black dot
There is a mysterious unlabelled black dot in his earlier observations of January 6, 1613, which is in the right position to be Neptune, Jamieson reported in the journal Australian Physics.

“I believe this dot could reveal Galileo went back in his notes to record where he saw Neptune earlier when it was even closer to Jupiter but had not previously attracted his attention because of its unremarkable star-like appearance,” he said.

While observing Jupiter, Galileo saw one of those “fixed stars”, seen in December 1612 and January 1613. It does not appear in any star catalogue. This particular “fixed star” turns out to be Neptune, which is yet to complete one orbit around the Sun since its official discovery, because its orbital period is 165 years. The first orbit will be completed in 2011.

 Galileo’s notes show he made several observations of the planet Neptune in December 1612 and January 1613. He uses the label “fixa” where he plotted the position of Neptune in his notebook, indicating, at least initially, that he believed he was observing a fixed star and not a planet.

 The notes of January 28, 1613, suggest he saw Neptune move when it passed in close conjunction to an actual star.
Yet it appears he did not follow up this observation, and no further entries in his notebooks have been identified that suggest Galileo was aware of the possibility of a new planet.
 The first two of three observations of Neptune were both made on December 28, 1612. The third observation was on January 28, 1613.

In between these two dates, Neptune was occulted by Jupiter. But there is a mysterious black dot on January 6, which the Australian physicist suggests was recorded on January 28. Jamieson proposed this would prove that Galileo believed he may have discovered a new planet. The unlabelled mark on January 6 might be a retrospective record made by Galileo after he observed the sky on January 28.

Tracing back the date
To prove his hypothesis, Jamieson suggested trace element analysis of the unlabelled spot from notes of January 6.

The effort will be to find out the precise date on which the dot was marked. If the analysis identified the date as January 28, it construed evidence that Galileo was thinking about the possibility of discovering a new planet. But are these techniques that accurate to distinguish two separate dates made within two weeks 400 hundred years ago? “Sufficient statistics (on one precise date) can be obtained without damage to the manuscript,” Jamieson told Deccan Herald.

The University of Florence has considerable experience in the analysis of Galileo’s inks using Proton Induced X-ray Emission (PIXE) method that was used in analysing Galileo manuscripts from 1600, 1605-09, 1617 and 1636. The analysis covered both the background parchment and the inks employed in the writing.

The technology was successfully used in accurately identifying dates within three months. But the bigger challenge now is to identify the date of the unlabelled spot on the ancient notebook as the gap is just two weeks. 

Published 27 July 2009, 12:16 IST

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