Pluto's Not a Planet (A Think)

Newspapers around the country and several Internet based news-sites are running articles explaining that a group of leading astronomers voted to change the definition of Pluto from a planet to a "dwarf-planet." An MSNBC article states:

Much-maligned Pluto doesn’t make the grade under the new rules for a planet: “a celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit.”

Lesson Ideas:
1. It's sometimes very difficult to define words like "planet." In order to help students understand this concept ask them to define the word "chair." Is a bean-bag a chair if somebody sits on it? What if a chair only has three legs? What if a chair has no legs, but fully sits on the ground? Does a chair have to have a back?
2. Ask students to consider why anyone should care if Pluto is categorized as a planet or as a dwarf-planet. This is a tough question to consider, so you might ask students to work in groups to first think about it. Challenge them to write down two or three serious reasons why this might matter. The article at MSNBC states, "It was unclear how Pluto’s demotion might affect the mission of NASA’s New Horizons spacecraft, which earlier this year began a 9½-year journey to the oddball object to unearth more of its secrets." Ask students to imagine that they are a scientist who has made Pluto their central area of study, they are reliant on the federal government and foundations to support their scientific studies. How do they think that this decision might effect the money that they receive?
3. Ask students to make up an imaginary conversation in which they compare life on Pluto, which used to be the furthest planet from the sun, to life on Mercury, the closest planet to the sun. To do this you might ask students to work in groups, one person would pretend that they are on each of the planets. This would be an interesting project to do on blogs.

One of the reasons that I chose to use MSNBC as the source of today's article is because the page, has interesting videos and charts on it.