Early views about the asteroids

The word 'asteroid' means 'star-like'. This name probably arose because, viewed through a small telescope from Earth, asteroids look like points of light.

Ancient observers on Earth did not know the asteroids because they cannot be seen with the unaided eye. The idea that a planet-like body might exist between the orbits of Mars and Jupiter was suggested by Johann

Elert Bode in 1768. In January 1801, the Sicilian astronomer Giuseppi Piazzi discovered a body in a position similar to that predicted by Bode. This body was called Ceres in honour of the Roman goddess of plants and harvest, and was the first asteroid to be discovered. In March 1802, the German astronomer Heinrich Olbers discovered another faint asteroid that he called Pallas (after the Greek goddess of wisdom). Two more asteroids discovered in the early 1800s were called Juno and Vesta.

By 1850, 10 asteroids were known to orbit at average distances from the Sun of between 2.2 and 3.2 AU. These early findings were made visually by astronomers who spent many hours at telescopes, observing changes in positions of celestial objects against the background of stars. In 1891, the German astronomer Max Wolf made the first photographic discovery of an asteroid. The object was named Brucia, and was the 323rd asteroid to be found. By 1923, the list of asteroids had grown to over a thousand.

During the early years of discovery, mythological names were given to the asteroids. All the early names were female. This naming scheme was later abandoned. Some asteroids are named after countries, for example, 1125 China, while others are named after people, for example, 2001 Einstein. Permanent numbers are assigned to asteroids once their orbits have been calculated and confirmed.

Table 8.1 Details about the largest asteroid Ceres (a dwarf planet)

Distance from Sun

413 700 000 km (2.76 AU)

Diameter

950 km in diameter

Mass

9.46 x 1020 kg

Density

2.07 g/cm3 or 2070 kg/m3

Orbital eccentricity

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