First Asteroid Is Discovered

The discovery of Ceres was an accident that occurred during a large, cooperative search for what was believed to be a missing planet between the orbits of Mars and Jupiter. The discovery led to the eventual cataloging of several thousand asteroids and a rethinking of the structure of the solar system.

Summary of Event

On the very first day of the nineteenth century, the Italian astronomer-monk Giuseppe Piazzi discovered the first asteroid from the observatory he had established in Palermo, Sicily. Sicily Although his discovery was accidental, it was not entirely unexpected. Toward the end of the eighteenth century, several astronomers had suspected that a “missing planet” might lie between the orbits of Mars and Jupiter. Piazzi made his discovery as astronomers were beginning to organize a systematic search for that planet. Asteroids
Ceres (asteroid)
[kw]First Asteroid Is Discovered (Jan. 1, 1801)
[kw]Asteroid Is Discovered, First (Jan. 1, 1801)
[kw]Discovered, First Asteroid Is (Jan. 1, 1801)
Ceres (asteroid)
[g]Solar system;Jan. 1, 1801: First Asteroid Is Discovered[0070]
[g]Italy;Jan. 1, 1801: First Asteroid Is Discovered[0070]
[c]Astronomy;Jan. 1, 1801: First Asteroid Is Discovered[0070]
[c]Science and technology;Jan. 1, 1801: First Asteroid Is Discovered[0070]
[c]Exploration and discovery;Jan. 1, 1801: First Asteroid Is Discovered[0070]
[c]Photography;Jan. 1, 1801: First Asteroid Is Discovered[0070]
[c]Mathematics;Jan. 1, 1801: First Asteroid Is Discovered[0070]
Piazzi, Giuseppe
Titius, Johann
Bode, Johann
Herschel, William
Zach, Franz Xaver von
Gauss, Carl Friedrich
Olbers, Heinrich
Kirkwood, Daniel
Wolf, Max

In 1766, the German astronomer Johann Titius Titius, Johann found that the positions of the known planets could be approximated by a simple mathematical Mathematics;and astronomy[Astronomy] formual. By adding the number 4 to each number in the sequence 0, 3, 6, 12, 24, 48, 96, and then dividing by 10, planetary distances from the Sun could be calculated in astronomical units (AU), with one AU representing the distance between Earth and the Sun. However, an exception occurred at the fifth position, where a gap appeared between the orbits of Mars and Jupiter at (4 + 24)/10 = 2.8 AU. Titius suggested that the gap might contain an unknown moon of Mars. The German astronomer Johann Bode Bode, Johann publicized Titius’s rule and predicted in 1772 that a missing planet might be found in the gap at 2.8 AU.

Bode’s prediction was reinforced when the German-English astronomer Sir William Herschel Herschel, William discovered the planet Uranus Uranus in 1781. When the distance of Uranus was measured at about 19 AU, it was found to compare well with the Titius-Bode rule for the next logical number in the sequence, giving a distance of (4 + 192)/10 = 19.6 AU. On September 21, 1800, the German-Hungarian astronomer Baron Franz Xaver von Zach Zach, Franz Xaver von organized a systematic search for a planet at 2.8 AU by dividing the heavens into twenty-four equal sections and assigning each section to a different astronomer. One of the chosen astronomers was Piazzi, whose Palermo observatory was the farthest south of any European facility. Even before these twenty-four so-called “celestial police” could begin their work, Piazzi Piazzi, Giuseppe made the accidental discovery of a faint object, which turned out to be the first asteroid.

A Theatine monk and priest, Piazzi was assigned as the chair of higher mathematics at the Academy of Palermo in 1780. There he established an observatory with the help of royal patronage from King Ferdinand III Ferdinand III of Sicily. While checking star maps against telescopic observations on the night of January 1, 1801, Piazzi found a dim, starlike object that was not on his maps and that changed its position from night to night. After observing the object for twenty-four nights, until he became too ill to continue, he reported what he thought might be a comet.

By the time other astronomers tried to check Piazzi’s results, the object he observed had receded behind the Sun. Piazzi was unable to work out the object’s exact orbit but showed that it was similar to a planetary orbit and estimated the distance of the object at 2.7 AU. Piazzi’s last contribution to the discovery of the object, if it could be recovered and confirmed, was to propose it be named Ceres Ferdinandea, in honor of Sicily’s patron goddess of agriculture, Ceres, and Sicily’s King Ferdinand III.

Carl Friedrich Gauss.

When the celestial police received Piazzi’s report, Bode Bode, Johann and several other astronomers immediately concluded that the object Piazzi Piazzi, Giuseppe had found was the missing planet. To facilitate recovery of the object, the young German mathematician Carl Friedrich Gauss Gauss, Carl Friedrich worked out a method to determine a precise orbit from three observations. His effort required the solution of seventeen equations but led to a successful recovery of the object on December 31, 1801, by Baron von Zach Zach, Franz Xaver von one year after its initial discovery. The object’s distance was measured at 2.77 AU with a period of 4.6 years, and its name was officially shortened to Ceres. When Herschel Herschel, William observed Ceres early in 1802, he concluded that it was only a fraction the size of Earth’s Moon, much too small to be a planet, and proposed the name “asteroid” (starlike) for minor planets such as it.

Because Ceres appeared to be too small to be a planet, the celestial police continued their search. On March 28, 1802, the German astronomer Heinrich Olbers Olbers, Heinrich found a second small object at the same distance as Ceres but with a more eccentric orbit. He named it Pallas after Pallas Athena, the Greek goddess of wisdom. Herschel then showed that Pallas was even smaller than Ceres.

Consistent with the Titius-Bode rule, Olbers proposed in 1803 that asteroids come from an exploded planet at 2.8 AU. This possibility led to a continuing search that resulted in the discovery of the asteroid Juno Juno (asteroid) in 1804 by the German astronomer Karl Harding and the discovery of Vesta Vesta (asteroid) in 1807 by Olbers at distances of 2.67 AU and 2.36 AU. Their approximate diameters and modern designations are 580 miles (33 kilometers) for 1 Ceres, 300 miles (483 kilometers) for both 2 Pallas and 4 Vesta, and 120 miles (193 kilometers) for 3 Juno. All these bodies are much smaller than Earth’s Moon, which has a diameter of about 2,135 miles (3,435 kilometers).

No additional asteroids were discovered until 1845, when the German astronomer Karl Hencke Hencke, Karl discovered 5 Astraea after fifteen years of observing. When Hencke discovered a sixth asteroid, 6 Hebe, in 1847, other astronomers returned to the search. Over the next forty-five years more than three hundred asteroids were discovered, mostly in the so-called main belt between 2.1 AU and 3.4 AU. Only the largest asteroids have spherical shapes, notably the three largest: 1 Ceres, 2 Pallas, and 4 Vesta.

In 1867, the American astronomer Daniel Kirkwood Kirkwood, Daniel discovered gaps in the main belt in which few asteroids have been found. These so-called Kirkwood gaps occur where the periods of asteroid orbits are simple fractions of the twelve-year period of massive Jupiter at 5.2 AU, and result from repeated gravitational forces called resonances.

In 1891, the pace of asteroid discoveries accelerated with the use of photography, Photography;and astronomy[Astronomy]
Astronomy;and photography[Photography] beginning with the work of the German astronomer Max Wolf Wolf, Max . Wolf used long exposures in which the movements of asteroids produced light streaks. Since then, several thousand additional asteroids have been cataloged, including 248 found by Wolf himself.


Asteroids provide important insights into the formation and nature of planets and meteorites. Olbers’s Olbers, Heinrich idea that asteroids came from an exploded planet at 2.8 AU has been discredited by the fact that asteroid orbits do not intersect at this distance, even though about half of their orbits are between 2.75 AU and 2.85 AU. Furthermore, their total mass is equivalent to only about 3 percent of the Moon’s mass. Astronomers now believe that asteroids are the debris left over after planet formation and that the gravitational forces caused by Jupiter’s large mass depleted much of this debris and prevented the rest from combining to form a single planet. Collisions among asteroids and their resulting fragmentation are believed to be the source of most of the meteorites that reach the surface of Earth. They represent the oldest material in the solar system from shortly before planet formation.

Asteroids have played significant roles in Earth’s history. Some are now known to have elliptical orbits that cross Earth’s orbit, probably as a result of past collisions in the main belt. Some of these have hit Earth in the distant past and left craters more than 60 miles (96 kilometers) in diameter that have been revealed by satellite photography. It is believed that some asteroid impacts have contributed to major extinctions of species, such as the dinosaurs, Dinosaurs;extinction of and perhaps even reversals of Earth’s magnetism. Astronomers now conduct regular surveys to detect such “killer asteroids” in order to provide warnings of possible collisions with Earth.

Further Reading

  • Hoskin, Michael, ed. The Cambridge Concise History of Astronomy. Cambridge, England: Cambridge University Press, 1999. Contains a useful chapter on the discovery of asteroids.
  • Jaki, Stanley L. “The Early History of the Titius-Bode Law.” American Journal of Physics 40 (July, 1972): 1014-1023. This article has an interesting account of the background of the discovery of asteroids.
  • Kaufmann, William J., and Roger A. Freedman. Universe. 5th ed. New York: W. H. Freeman, 1999. Chapter 17, “Vagabonds of the Solar System,” offers a good introduction to the search and discovery of asteroids.
  • Peebles, Curtis. Asteroids: A History. Washington, D.C.: Smithsonian Institution Press, 2000. A comprehensive account of the two-century history of asteroid discovery.
  • Watson, Fletcher G. Between the Planets. Cambridge, Mass.: Harvard University Press, 1956. The early chapters provide good accounts of the discovery and properties of asteroids.

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