Ceres: The First Asteroid

Ceres: The First Asteroid

The nineteenth century began with an astronomical bang: the discovery of an apparent planet between the orbits of Mars and Jupiter. However, the “planet” discovered on January 1, 1801, wasn’t really a planet at all. Instead, it was the largest example of a new class of object – an asteroid. The new-found object was later named Ceres.

Giuseppe Piazzi, a Sicilian priest and astronomer, discovered Ceres accidentally while mapping a section of the sky. Over a period of several nights Piazzi watched as this new object, which he originally believed to be a comet, moved steadily against the background of stars. When it reversed directions, as all planets do periodically, it seemed that the astronomer had found a “missing” planet.

Thanks to a simple mathematical relationship called Bode’s Law, astronomers of the day believed that a planet must exist in the wide gap between the orbits of Mars and Jupiter. Until Piazzi’s discovery, though, no one could find it.

Ceres. The history of astronomy is a history of receding horizons. (Edwin Powell Hubble). Photo of Ceres: Public domain

Piazzi became ill shortly after discovering the mysterious object. And by the time word of his findings reached other astronomers, Ceres had moved too near the Sun for anyone to observe it.

Meanwhile, a young German mathematician, Karl Friedrich Gauss, used Piazzi’s observations to calculate the object’s orbit. Gausse correctly predicted when and where the object would re-emerge from the Sun’s glare, and the “planet” was rediscovered on December 31, 1801. It was later named Ceres after the Roman goddess of agriculture.

And there, Piazzi and other astronomers thought, the story would end. It did not. In March 1802, a second body was discovered in an orbit similar to Ceres’. Thousands of others have been found since.

The Cosmos. Illustration by Elena.