This is good news for students! Now they only have to remember 8 instead of 9 since Pluto is not a “planet” anymore.
1) Press release by the International Astronomical Union (IAU) here:
http://www.iau2006.org/mirror/www.iau.org/iau0603/index.html
Highlights:
‘a “planet” is defined as a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit. ‘
‘This means that the Solar System consists of eight “planets” Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.’
2) The press release on the formal definition can be found here:
http://www.iau2006.org/mirror/www.iau.org/iau0602/index.html
3) Wikipedia has a well updated article on it too:
http://en.wikipedia.org/wiki/2006_redefinition_of_planet
4) The NYTimes has also an editorial on it (you might need an subscription):
Title: And Now There Are Eight
Date: August 25, 2006
http://www.nytimes.com/2006/08/25/opinion/25fri3.html?th&emc=th
