27 August 2006

How Many Planets Are There in the Solar System?

In increasing distance from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. In total, eight.

Yep, if you're not aware of recent astronomy news, it appears that Pluto, our eccentric fringe member in the Solar System, has been voted out of the Planetary Club, as a result of a re-definition of the term "planet".

Of course, the status of Pluto as a planet has been in question for a long time, mainly due to its small size, highly eccentric orbit and tilted plane of orbit. The reason why it was labelled as a planet is a long story, which can be simply summarised into two points. One, theoretical calculations based on Neptune's orbit inferred a presence of massive objects beyond, which was assumed to be a planet (though it turned out later to be more than a "planet"). Two, telescopes weren't that accurate in the 1930s when Pluto was discovered, so its size and orbit could not be determined accurately.

So, how will that change things? It won't. Pluto, as a planet or a dwarf planet (its new label), will continue to orbit eccentrically in an inclined plane no matter what we call it. Celestial objects couldn't be bothered with those mundane labellings that morons on the third planet from the Sun are so fascinated with.

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