A Brief History of Ceres: “The Missing Planet”

Almost a ‘Lost Comet

As of spring 1801, besides Piazzi, no one had been able to observe the new celestial object because of cloudy skies and the object’s position in its orbit — it was no longer visible at night, and the sun blocked astronomers’ views. Meanwhile, Piazzi still did not publish anything on the object, while he continued to refine his data. Several of his colleagues grew upset with Piazzi for holding back information. Without the data from his observations that concluded on Feb. 11, confirming his discovery would be more difficult — since February, Ceres had been lost.

Why did Piazzi hesitate to make his data public? One reason might be that, though Piazzi was a skilled observer, he didn’t have a solid theoretical knowledge of astronomy, so he couldn’t calculate orbits quickly. Secondly, he risked the credibility and reputation of both himself and the observatory. But while he wavered, colleagues in Germany such as Bode firmly believed that there needed to be a planet between Mars and Jupiter. It was their conviction that helped keep the work going on this object, said Ileana Chinnici, who edited the Palermo Observatory’s booklet on Ceres.

“Without the determination of the German astronomers, Piazzi would have been just the discoverer of a lost comet, in the best case. They ‘believed’ in the existence of the planet and were driven by the endeavor to confirm it. This shows how powerful are ideas, models, theories — yesterday as well as today,” Chinnici said.

At last, in July 1801, Piazzi worked on calculating the object’s orbit and made public his data about his observations from earlier in the year. And while other astronomers had already come up with their own names — such as Juno, Hera and Piazzi (to honor the astronomer) — Piazzi himself announced that the “new star” was called Ceres Ferdinandea. The “Ferdinandea” part honored King Ferdinand of Sicily.

Ceres, the Roman goddess of agriculture, was also the patron deity of Sicily, where Piazzi then lived and worked. Bode, who had wanted to call the object Juno, agreed on Ceres: “You have discovered it in Taurus, and it was re-observed in Virgo, Ceres of the old times. These two constellations are the symbol of agriculture. This occurrence is quite unique.”

By the end of July 1801, many astronomers believed Ceres was a planet, but they needed additional confirmation and observations. Piazzi published his complete data set in von Zach’s journal in September and, by doing so, got the attention of a young mathematician who would become instrumental in the fate of Ceres.

Twenty-four-year-old Carl Friedrich Gauss had been experimenting with mathematical methods for which he would later become famous. When he applied those methods to Ceres, he came up with different predictions for its position than what others had calculated. Though some were skeptical about Gauss’s results, his calculations enabled von Zach to be the first to see Ceres again, on Dec. 7, 1801, followed by other prominent astronomers of the time, and by Piazzi himself on February 23, 1802.

We credit Gauss for calculating the orbit of Ceres. But he did not resolve a fundamental question: What is Ceres?

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