| 1) In ancient times, Greek astronomers
noticed that there were certain
lights in the night sky that seemed to move across the sky in relation
to the stars. The Greeks called these moving lights ‘planetes’ a Greek
term meaning a wanderer. From this comes our word planet. As the
science of astronomy became more sophisticated it was noticed that
there were nine such planets in our solar system. They were named
Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and
Pluto. 2) Historically there had been no formal definition of a planet and the discovery of other large celestial bodies in our solar system, most notably Ceres, Sedna and Eris, led to a debate over what exactly a planet is. 3) In 2006, the International Astronomical Union decided on a three-point definition of a planet within our solar system. 4) A new category, named a dwarf planet, was introduced to describe those large celestial bodies that satisfied the first two points of the definition decided in 2006, but not the third. 5) Back in 1930, a new planet had been discovered at the edge of our solar system. 6) For many years, Pluto was thought of as the farthest known planet from the Sun and the ninth planet in our solar system. 7) It seems that the heavens are changing not only above our heads but in the minds of men. The 2006 decision of the International Astronomical Union has reduced the number of planets in our solar system from the long accepted total of nine to the currently accepted figure of eight. It is hard not to think of Pluto as a planet, as most of us have all our lives, but the experts have decreed it is not. |
| This
article is about..... |
Clues |