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CERES
 Ceres was
discovered in 1801 and is the largest object orbiting the Sun in the
Asteroid Belt between Mars and Jupiter. Up to August 2006, Ceres was
recognised as an asteroid until scientists voted to redefine what a planet
actually is. By doing this, they created a new kind of planet - the Dwarf
Planet - and Ceres found itself fitting into the definition of what a Dwarf
Planet is! Its title suggests that a Dwarf Planet is a small planet, a round
world which orbits the Sun. This is basically true (all current dwarf
planets are smaller that the Moon orbiting Earth), but a Dwarf Planet is
also different to regular planets because it hasn't "cleared the
neighbourhood around its orbit". Each regular planet (Mercury,
Venus, Earth, Mars,
Jupiter, Saturn, Uranus and
Neptune) travels around the Sun.
Most of these planets are accompanied by moons which spin around them.
However, apart from the odd meteor, there is nothing else in the way of the
planet on its route around the Sun. This is because the planet has
"cleared" its route, either by absorbing any objects during its
formation billions of years ago, or by capturing them to become a moon, or
by flinging them away. Dwarf Planets don't have a clear route. Pluto, which
was recognised as a planet since 1930 until being reclassified as a Dwarf
Planet, crosses the orbit of Neptune, meaning that its orbit hasn't been
cleared. And because Ceres orbits the Sun in the Asteroid Belt, there are a
number of asteroids in its path, meaning that it too doesn't have a clear
route. But, because it is round and orbits the Sun, the new category of
planet means that instead of being continuing to be recognised as an
asteroid, Ceres is now a Dwarf Planet!
The early classification of
Ceres is similar to the reclassification of Pluto. Of the three current Dwarf
Planets, Ceres was the first to be known about. It was discovered on 1st January
1801 by Italian astronomer, Guiseppi Piazzi. So, when everybody else was
watching fireworks going off to celebrate the New Year, Guiseppi was standing in
his back garden finding Dwarf Planets! Originally, Guiseppi Piazzi thought he
had found a comet (must have been those New Year fireworks again), but noticing
how it moved, realised it was something else. Shortly after its discovery was
confirmed, Ceres was actually classified as a planet and became the eighth planet in the Solar System
known about at the time (Uranus was discovered earlier in 1751).
About 50 years later, it was realised that Ceres was one of a number of similar
objects orbiting the Sun in its area. It lost its status as a planet and was
reclassified as an Asteroid, or Minor Planet. The area it orbits was called the
Asteroid Belt. As an Asteroid, It was called 1 Ceres because it was the first
object of its kind to be discovered. The Minor Planet Center (MPC), which
collects data about all asteroids and comets and calculates their orbits,
records Ceres of Minor Planet 1. Just to confuse things, a Minor Planet is not a
Dwarf Planet. All asteroids and comets are given MPC numbers. 
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In
2006, the International Astronomical Union met in the Czech Republic to discuss
the state of the Solar System. It was getting a mess and needed sorting out!
More and more objects were getting discovered in the Solar System - round
objects like Pluto - but it was getting difficult to decide what to call them.
Should they be planets, asteroids, comets, planetoids, plutons,
meatballs.......? A proposal was put forward to call just about all round
objects which orbit the Sun "planets". This would have meant that
Pluto's moon, Charon, would become a planet (since it orbits the Sun with
Pluto, not around Pluto), the newly discovered
Eris would be a planet,
and Ceres would also become a planet again! However, the scientists at the
meeting didn't really like this idea, fearing that the Solar System would
contain tens - even hundreds - of planets, most of which are relatively
insignificant compared to the eight traditional planets. So, they voted to
create the new category of Dwarf Planet, and Ceres instantly became classified
as one!  Ceres is
about 950 kilometres in diameter and takes just over four and a half years to
complete an orbit around the Sun. Ceres can be seen without a telescope or
binoculars, but you would need to be very sharp-sighted with no external
interference (moonlight, artificial lights, clouds) to spot it. It is thought
that Ceres' internal temperature is quite high as surface temperatures have been
estimated to reach a maximum of -38c. Ceres is likely to be cratered, although
imaging of the object has not revealed a great deal of information about its
surface. More information about Ceres should come when NASA sends its probe,
Dawn, to visit in 2014. Before getting to Ceres, Dawn will spend six months
observing 4 Vesta, now the largest asteroid in the Asteroid Belt, probably in
2010.
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