Piazzis planet

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The discoverer was defiant: 'I have the full right to name it in the most convenient way to me, like something I own. I will always use the name Ceres Ferdinandea, nor by giving it another name will I suffer to be reproached for ingratitude towards Sicily and its king.'

Shortly after nightfall on 1 January 1801, Giuseppe Piazzi, a monk and director of the brand new Palermo Observatory built atop a 12th-century tower in the royal palace of Sicily, pointed his shining brass telescope at stars in the constellation Taurus and observed an unfamiliar, faint, starlike object. Later observations and calculations showed it to be the 'missing planet' between Mars and Jupiter. He named it Ceres Ferdinandea -Ceres for the patron goddess of Sicily, and Ferdinandea for his royal patron, King Ferdinand of Naples and Sicily.

The discovery caused a sensation in Europe. The burning question was: what should the new planet be named? Napoleon even discussed it with the celebrated French mathematician and astronomer Pierre Laplace. Some French astronomers suggested Piazzi, while some Germans favoured Juno or Hera. But Piazzi was adamant that he had the right to name it.

The story of Piazzi's discovery starts in 1772, when Johann Titius, a professor at Wittenberg in Germany, discovered a remarkable numerical relationship between the distances of the planets from the Sun. He pointed out that the numbers in the series 0, 3, 6, 12, 24, 48, 96, when added to 4 and divided by 10, produced the series 0.4, 0.7, 1, 1.6, 2.8, 5.2, 10. If Earth's distance from the Sun is set at 1 astronomical unit (about 150 million kilometres), then these numbers give the distances of the six planets known at the time, except for position 2.8. Titius suggested that this gap belonged to still undiscovered satellites of Mars.

That same year, the German astronomer Johann Bode picked up Titius's rule and quoted it without any acknowledgement in his astronomy textbook. However, he suggested a new planet for the gap at 2.8. The rule is now known as Bode's law. Although Bode also carried out other astronomical investigations, he is remembered today for popularising a relationship that he did not originate.

When the celebrated German-British astronomer William Herschel discovered the planet Uranus in 1781, it also fitted Bode's law (continuing the Titius series by doubling 96 for Saturn, that is, 192; when added to 4 and divided by 10, this gives 19.6, which is close enough to 19.2, the actual distance of Uranus from the Sun in astronomical units). Astronomers now strongly felt that another planet was to be found between Mars and Jupiter.

The Hungarian astronomer Franz von Zach so strongly believed in the 'missing planet' that he tried to calculate its orbit by using Kepler's laws, but one element that might reveal its location - the longitude - eluded him. In 1785 he wrote to Bode: 'I am having much the same success as the alchemists in their search for gold; they had everything except the vital factor. Thus I too believe that I am in possession of all the elements of the orbit of this still unknown planet, except one; this alone now keeps me amused, and although one may not find gold in one's wanderings, one does occasionally come across a chemical process.'

In 1787 von Zach took a solo search for the planet, but without success. 'It cannot be a matter for one or two astronomers to scrutinise the entire Zodiac', he wrote in Monatliche Correspondenz (Monthly Correspondence), the world's first astronomical journal, which he founded. The hunt for the missing planet began in earnest when, in 1800, von Zach organised a group of 24 astronomers who called themselves the 'celestial police'. They divided the entire Zodiac into 24 zones. The zones were then allocated to the members by lot. Each member was to be responsible for drawing up a star chart for his zone.

'Through such a strictly organised policing of the heavens, divided into twenty-four sections, we hoped eventually to track down this planet, which had so long escaped our scrutiny - supposing, that is, that it existed and could be seen', von Zach wrote in Correspondenz. Before 'such a strictly organised policing' of the heavens could get under way, surprising news arrived from Palermo on the island of Sicily.

Giuseppe Piazzi, a Theatine monk who entered the order in 1764 at the age of eighteen, received his early training in philosophy but later in life took up mathematics and astronomy. In 1780 he was called to the chair of higher mathematics at the Academy of Palermo. There he soon obtained a grant for an observatory, and he went to England in 1788 to buy instruments for it. He commissioned Jesse Ramsden, the greatest of the instrument-makers, to make him a 1.5-metre vertical circle of unique design for measuring the altitudes and azimuths of stars by micrometer microscopes. While in England he became acquainted with Herschel and had the unique 'privilege' of falling off the high wooden ladder at Herschel's large reflecting telescope and breaking his arm.

Once the Ramsden circle, the masterpiece of 18th-century technology, was installed at Palermo in 1791, Piazzi started his painstaking work of cataloguing stars. In 1803 he published his first catalogue containing 6,784 stars, and in 1814 a second one containing 7,646 stars. However, Piazzi's major accomplishment did not involve the stars at all. It was the discovery of the 'missing planet'.

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