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rule predicts a planet should exist between Mars and Jupiter, though no planet was known to be there. There began a significant effort to find this missing planet, leading to the discovery of the main asteroid belt.

In 1800, a Hungarian baron named Franz Xavier von Zach, astronomer to the duke of Gotha and director of the Seeberg Observatory, sponsored a special search for the suspected missing planet. The initial group of six astronomers met for a conference in Lilienthal, Germany. Additional astronomers were invited to join until the illustrious group totaled 24:

• Johann Elert Bode in Berlin, director of the Berlin Observatory, founder of the journal Berliner Astronomische Jahrbüche, who named Uranus after William Herschel discovered the new planet

• Thomas Bugge in Copenhagen, a Danish professor of mathematics and astronomy and director of the Copenhagen Observatory

• Johann Carl Burckhardt in Paris, who was born in Leipzig but became a naturalized Frenchman and succeeded Joseph-Jérôme Le Français de Lalande as director of the Paris Observatory

• Johann Tobias Bürg in Vienna, a professor at the University of Vienna and assistant at the Vienna Observatory who was commended by the French Academy for his computations concerning the Moon

• Ferdinand Adolf von Ende in Celle

• Johann Gildemeister in Bremen

• Karl Ludwig Harding in Lilienthal, a professional astronomer who discovered three comets

• William Herschel in Slough, an amateur astronomer who made immense contributions to the field, including the discovery of Uranus, the first new planet discovery since prehistoric times

• Johann Sigismund Gottfried Huth in Frankfurt

• Georg Simon Klügel in Halle, a mathematician most famous for discoveries in trigonometry and for his dictionary of mathematics

• J. A. Koch in Danzig (Gdansk), an astronomer who discovered the fifth known variable star

• Nevil Maskelyne in Greenwich, director of the Royal Observatory

• Pierre-François-André Mechain in Paris, a close collaborator with Messier on surveys of deep space and comet searches

• Daniel Melanderhielm in Stockholm, professor of astronomy in Uppsala

• Charles Messier in Paris, the Astronomer of the Navy in France, one of the most prominent figures in the history of astronomy, creator of the Messier catalog of nebulas, and discoverer of 20 comets

• Heinrich Wilhelm Mattäus Olbers in Bremen, who was principally a physician but excelled as an astronomer in his spare time and developed one of the first functional techniques for calculating the orbit of a comet

• Barnaba Oriani in Milan, director of the Brera Observatory

• Giuseppi Piazzi in Palermo, professor at the University of Palermo who went on to find the first asteroid without having received his invitation to join the society

• Johann Hieronymus Schroeter in Lilienthal, an administrator and lawyer whose astronomical papers and findings along with those of von Ende and Harding were lost when Lilienthal was burnt by Napoleonic forces in 1813

• Friedrich Theodor Schubert in St. Petersburg, a professor of mathematics and astronomy

• Jons Svanberg in Uppsala

• Jacques-Joseph Thulis in Marseille, director of both the academy and the observatory in Marseille

• Julius Friedrich Wurm, professor at Blauebeuren, Germany

• Franz Xavier von Zach, founder of the society, director of the Gotha Observatory

They divided the sky into 24 zones along the zodiac (recall that the constellations of the zodiac lie on the arc across the sky that the planets appear to travel, when seen from Earth, so any new, unidentified planet would be expected to travel the same path) and assigned each of the zones to an astronomer.They named themselves the Vereinigte Astronomische Gesellschaft, commonly called the Lilienthal Society. They came to be known more widely by the charming name Celestial Police (Himmel Polizei) because they were charged to "arrest" the missing planet. Their search was made possible by the advances in telescopes that had been made since the invention of the device in 1608.

On January 1, 1801, Giuseppi Piazzi, a Sicilian monk making his nightly observations from a telescope atop the royal palace in Palermo, sighted the first orbiting asteroid known to humans. He saw a faint object that was not listed on the star maps. At first he thought it was a comet, since comets were the only type of orbiting object that humans had ever seen, aside from the planets. As he continued to observe it, he saw that it did not look or move like a planet, and he began to suspect, as he wrote, that it "might be something better."

Gioacchino Giuseppi Maria Ubaldo Nicolo Piazzi had been born to a noble family and, while he had joined an order of monks, he also held the chairs of mathematics and astronomy at the respected

University of Palermo. In the years before 1801, Piazzi had traveled throughout Europe visiting other scholars, and then oversaw the building of one of the world's most advanced telescopes at the palace in Palermo. Piazzi's name is on the list of the Celestial Police although they neglected to formally invite him, and at the time of his discovery, he was ignorant of his inclusion. Piazzi was notified of his invitation indirectly through another member, Oriani, in May 1801, after the dwarf planet Ceres had been discovered.

During his detailed observations of this new body, he fell sick and had to give up observations for a time.When he recovered, he went eagerly to resume his study of this strange new object, but he could not find it, as it had moved too near the Sun in its orbit. Piazzi notified the scientific community of his observations, but no one could find the celestial body. Not even the famous astronomer William Herschel could find it. At last the astonishingly brilliant mathematician Carl Friedrich Gauss, only 24 at the time, took Piazzi's observations and calculated where in the sky the body should now be found, based on the current knowledge of orbital dynamics. He passed his calculations to von Zach, the founder of the Celestial Police, who immediately found the body exactly where Gauss said it should be.

At first this body was thought to be the missing planet between Mars and Jupiter, but soon it was realized that the body was just too small. Piazzi named the tiny object Ceres (actually, he named the asteroid Ceres Ferdinandea, after King Ferdinand of Sicily, but this addendum was later challenged and dropped).The discovery of Ceres fueled the energy of the Celestial Police. In 1802, Olbers found a second tiny object and named it Pallas, and in 1804, Harding found a third, Juno. Olbers discovered Vesta in 1807, and that was the final discovery of a small body by the Celestial Police. Bode was troubled by these findings, as were other members of the scientific community, because the tiny size and number of these bodies seemed to disrupt the natural harmonious order of the planets. Would the maker of the universe have left a gap in the order of the planets, the community wondered? Briefly the idea arose that a planet had existed and was shattered, but a universe subject to such immense and capricious forces of nature was horrifying to those men of the enlightenment.

Within a month of the discovery of Pallas, scientists began to realize that a new class of solar system objects had been discovered. Herschel suggested naming these small bodies asteroids, which means

"starlike," because the movement of a bright orbiting asteroid seen through a telescope was reminiscent of the tracks of stars across the night sky as the Earth turns. (There was also a small movement to call them "planetkins.") In 1815, the Celestial Police finally stopped hunting for the missing planet, having concluded that only a collection of small bodies took up those orbits between Mars and Jupiter.

Following the discovery of Vesta in 1807, no further asteroids were discovered until 1845. By 1857, about 50 asteroids had been discovered, including Juno (diameter about 150 miles, or 240 km), Astraea (74 miles, or 119 km), Hebe (115 miles, or 185 km), Iris (127 miles, or 203 km), Flora (84 miles, or 135 km), and Metis (115 miles, or 184 km). By 1900,463 asteroids were known. Initially each asteroid was also assigned a symbol (much as the planets have symbols), but this system quickly became cumbersome as the numbers of discovered asteroids multiplied. Several of these symbols are shown in the figure here.

By about 1850, a system of temporary numbers, called "provisional designations," had been developed for assignment to each new possible asteroid discovery. It was thought at the time that there would be no more than 26 new discoveries per half-month, and so each half-month of the year is assigned a letter: The first half of January is called A, the second half B, the first half of February C, and so on.Within each half-month, new discoveries are given letter designations as well, with the first asteroid of each half-month called A. For example, the first asteroid discovered in the second half of February of the year 2004 has the provisional designation 2004 DA (the D is for the second half of February, and the A means the first asteroid of that month).

Unfortunately, this system quickly became too constraining, as the rate of asteroid discoveries accelerated. By the 1890s, photographic film could be used to search for asteroids: As shown in the upper color insert on page C-1, if a camera's shutter is left open for some period of time, an asteroid moves fast enough to appear as a streak, while stars in the background are more stable. If more than 26 new asteroids are discovered in a half-month, then the next asteroid gets the designation A , and the next B , and so on through the next alphabet, until it is used up and a third alphabet begins, with designation A2, and so on. The last asteroid discovered in one especially productive half-month was designated 1998 SL , meaning the namers had gone halfway

Many solar system objects have simple symbols, including the Sun, the planets, and some asteroids.

Symbol Collection

Symbols for Asteroids, Symbols for Planets or Dwarf Planets

Ceres

Pallas

Juno

Ç Mercury Sun

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